JP5362250B2 - Receiving apparatus and receiving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the time before the detection of frame synchronization. <P>SOLUTION: The receiver includes a plurality of correlation calculation means for calculating correlation information by executing processing corresponding to frequency deviations respectively different from each other to the sequence of reception symbols, and detects the arrival of synchronizing signals on the basis of one piece of the correlation information satisfying a prescribed condition among the plurality of calculated correlation information and the frequency deviation corresponding to the correlation information. In such a manner, the time before the detection of the frame synchronization is shortened. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a receiver for digital terrestrial broadcasting, for example.

  As a method for modulating digital data, a modulation method called an orthogonal frequency division multiplexing method (hereinafter referred to as an OFDM method; OFDM: Orthogonal Frequency Division Multiplexing) is known.

  In the OFDM method, a large number of orthogonal subcarriers (carriers) are provided in a transmission band, and data is allocated to the amplitude and phase of each carrier by PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation) and digitally modulated. It is a method. Since the OFDM scheme divides the transmission band with a large number of carriers, the band per carrier wave is narrowed and the modulation speed is slow, but the total transmission speed is the same as the conventional modulation system. Yes. In addition, since the OFDM scheme transmits a large number of carriers in parallel, the symbol rate is slow, the time length of the multipath relative to the time length of the symbol can be shortened, and it is difficult to receive multipath interference. It has characteristics. In the OFDM method, since data is allocated to a plurality of carriers, an IFFT (Inverse Fast Fourier Transform) arithmetic circuit that performs inverse Fourier transform during modulation, and an FFT (Fast Fourier Transform) that performs Fourier transform during demodulation. By using the arithmetic circuit, a transmission / reception circuit can be configured.

  The OFDM system is often applied to terrestrial digital broadcasting that is strongly affected by multipath interference. As terrestrial digital broadcasting adopting the OFDM system, for example, there is a standard such as ISDB-T (Integrated Services Digital Broadcasting-Terrestrial).

  In the ISDB-T standard, in addition to a data carrier for transmitting main information such as video information and audio information, an AC carrier for transmitting additional information and a TMCC (Transmission and Multiplexing Configuration Control) signal are transmitted. A TMCC carrier, an SP carrier and a CP carrier used for transmission path estimation at the receiver are defined. These various carriers are transmitted at predetermined carrier positions in the OFDM symbol. Among these, for the AC carrier and the TMCC carrier, DBPSK (Differential Binary Phase Shift Keying) modulation is adopted as a carrier modulation method. In DBPSK modulation, a data string to be transmitted is differentially encoded, and (+4/3, 0) and (-4/3, 0) signal points are obtained for information (0, 1) after differential encoding, respectively. This is a modulation method for making a complex signal (I, Q signal) having.

  The ISDB-T standard stipulates that an OFDM frame is composed of 204 consecutive OFDM symbols. The TMCC signal is composed of 204 bits, and this is transmitted one bit per OFDM symbol, so that one TMCC signal is eventually transmitted for each frame. The breakdown of the 204-bit TMCC signal consists of 1-bit differential modulation reference signal, 16-bit synchronization signal, 3-bit segment format identification, 102-bit TMCC information, and 82-bit parity bits from the beginning of the frame. It has become. Of these, the synchronization signal is transmitted to facilitate frame synchronization processing in the receiver, and the sync word W0 = “0011010111101110” and its inverted word W1 = “1100101000010001” are alternated in units of frames. Has been transmitted. The segment format identification is information indicating whether transmission data is differentially modulated or synchronously modulated. The TMCC information is information indicating a carrier modulation scheme of a received signal, a time direction interleave pattern, a coding rate of a convolutional code, and the like. The parity bit is an error correction code for the TMCC information of 102 bits, and a shortened code (184, 102) of the difference set cyclic code (273, 191) is adopted as the system.

  In an OFDM receiver compliant with the ISDB-T standard, before starting to demodulate main information such as video information and audio information, ICFO value detection processing and correction processing, and further, synchronization signals in the TMCC signal are processed. It is necessary to perform frame synchronization processing to detect and synchronize the OFDM frame.

ICFO detection / correction processing detects and corrects an ICFO (Integral Carrier Frequency Offset) value, which is a component that is an integral multiple of the carrier frequency interval, among carrier frequency errors caused by imperfections in the local oscillator of the receiver. It is processing. As an ICFO value detection method, a method of detecting the position of a DBPSK modulation carrier from a reception carrier and performing pattern matching between this detection result and a known DBPSK modulation carrier arrangement is common. As a method for detecting the position of the DBPSK modulation carrier from the reception carrier, a method using the fact that the average power of the DBPSK modulation carrier is larger than other data carriers, or the phase uncertainty of the DBPSK modulation carrier after differential demodulation is ± A method (for example, Non-Patent Document 1) utilizing the fact that the angle becomes 180 ° is known.
"Study of frequency synchronization method for OFDM demodulation"-1997 IEICE Communication Society Conference (page 331)

  However, if the frame synchronization process is performed after the ICFO detection process and the ICFO correction process are performed as described above, the output of the image and the sound is delayed accordingly. For example, when a synchronization signal arrives during ICFO detection processing and ICFO correction processing, it is necessary to wait for the next frame, and one frame is delayed, so it takes a long time to detect frame synchronization. It was.

  The problem to be solved by the present invention includes the above-described problem as an example.

In order to solve the above-mentioned problem, the invention according to claim 1 is a receiver for receiving an OFDM signal having a transmission unit of an OFDM symbol composed of a plurality of carriers and decoding the transmitted main information sequence. A signal is composed of a fixed number of OFDM symbols that are continuous in time to form one OFDM frame, and control information including a synchronization signal having a predetermined number of bits is transmitted for each OFDM frame by one or more specific carriers of the OFDM symbol. And carrier detection means for detecting the received OFDM signal and outputting a reception symbol composed of a plurality of reception carrier values, and processing for each of the receptions according to different frequency deviation values. A plurality of synchronization detection means for detecting the arrival of the synchronization signal for each symbol, performed on a sequence of symbols , A receiver for Ru wherein the synchronization detecting unit extracts the received carrier value corresponding to the control information transmission carrier from the received symbols in response to the frequency deviation value, on the extracted received carrier value Control information demodulating means for calculating a control information demodulated value by performing processing according to the frequency deviation value, and soft correlation for calculating a soft correlation value by performing a correlation operation between the control information demodulated value sequence and the synchronization signal comprising a calculation unit, wherein the symbol point either has detected the arrival of the synchronizing signal based on the soft phase correlation value of the synchronous detection means, the frequency deviation value when this synchronization detection means has detected the synchronization signal corresponding And the main information sequence is decoded from the OFDM signal. Here, a TMCC signal can be exemplified as the control information.

In order to solve the above-mentioned problem, the invention according to claim 5 is a receiving apparatus for receiving an OFDM signal whose transmission unit is an OFDM symbol composed of a plurality of carriers, wherein the OFDM signal is a certain number of OFDMs that are continuous in time. One OFDM frame is composed of symbols, and control information including a synchronization signal having a predetermined number of bits is continuously transmitted for each OFDM frame by one or more specific carriers of the OFDM symbol and received. Carrier detection means for detecting the OFDM signal and outputting a reception symbol composed of a plurality of reception carrier values, each of which performs processing corresponding to a different frequency deviation value on the received symbol sequence, thereby generating a soft correlation A plurality of correlation calculation means for outputting a value and a hard correlation value, and a plurality of soft correlation values calculated for each symbol. A soft correlation value that satisfies a predetermined selection condition is output as a maximum likelihood soft correlation value, and a frequency deviation value corresponding to the correlation calculation means that outputs the maximum likelihood soft correlation value is set as a maximum likelihood frequency deviation value. Maximum correlation detection means for outputting a hard correlation value output by the correlation calculation means for calculating the correlation value as a maximum likelihood hard correlation value, and arrival of a synchronization signal based on the maximum likelihood soft correlation value and the maximum likelihood hard correlation value a synchronization detecting means for detecting, a receiving device Ru wherein the correlation calculating unit extracts the received carrier value corresponding to the control information transmission carrier from the received symbols in response to the frequency deviation value, is extracted A control information demodulating means for calculating a control information demodulated value by performing processing according to the frequency deviation value on the received carrier value, and performing a correlation operation between the control information demodulated value sequence and the synchronization signal; Soft Soft correlation calculation means for calculating a function value, hard correlation value calculation means for calculating the hard correlation value by performing a correlation operation between a sequence obtained by performing binary determination of the control information demodulated value and the synchronization signal; The main information sequence is demodulated from the OFDM signal according to the symbol time when the synchronization detection means detects the arrival of the synchronization signal and the maximum likelihood frequency deviation value at that time.

In order to solve the above problem, the invention according to claim 10 is a reception method for receiving an OFDM signal having a transmission unit of an OFDM symbol composed of a plurality of carriers, and decoding the transmitted main information sequence. A signal is composed of a fixed number of OFDM symbols that are continuous in time to form one OFDM frame, and control information including a synchronization signal having a predetermined number of bits is transmitted for each OFDM frame by one or more specific carriers of the OFDM symbol. And a carrier detection step of detecting the received OFDM signal and outputting a reception symbol composed of a plurality of reception carrier values, and processing each corresponding to a frequency deviation value different from each other. A plurality of synchronization detections are performed on a symbol sequence to detect the arrival of the synchronization signal for each symbol. A step, a receiving method Ru wherein the synchronization detection step extracts the received carrier value corresponding to the control information transmission carrier from the received symbols in response to the frequency deviation value, the extracted received carrier value On the other hand, a control information demodulation step for calculating a control information demodulated value by performing processing according to the frequency deviation value, and performing a correlation operation between the sequence of the control information demodulated value and the synchronization signal to calculate a soft correlation value And a frequency corresponding to a symbol time point at which one of the synchronization detection steps detects arrival of the synchronization signal based on the soft correlation value, and a synchronization detection step at which the synchronization signal is detected at this time. The main information sequence is decoded from the OFDM signal according to the deviation value.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram of an ISDB-T television broadcast demodulator (corresponding to a receiving apparatus) according to the present embodiment. FIG. 2 shows parameter specifications used in the following description of the embodiment. Hereinafter, description will be made with reference to the parameter specifications shown in FIG.

  An ISDB-T television broadcast demodulator (hereinafter referred to as “television broadcast demodulator”) 1 shown in FIG. 1 includes a carrier detection unit 2, a frame synchronization unit 3, and a main demodulation unit 4.

The carrier detection unit 2 performs processing such as channel selection, filtering, AD conversion, quadrature detection, symbol synchronization, symbol extraction, and FFT on the input RF signal (reception signal) to obtain N _FFT received carriers. Output a series of received symbols consisting of values.

  The frame synchronizer 3 generates a symbol count according to the input received symbol sequence and supplies it to the main demodulator 4, and detects and corrects ICFO caused by imperfections of the carrier detector 2. As described above, feedback control is performed on the carrier detector 2. Here, the symbol count indicates the position of the received symbol in the frame structure. The frame synchronization unit 3 has a synchronization detection mode and a synchronization holding mode.

  The main demodulator 4 performs processing such as channel estimation, equalization, deinterleaving, and error correction in accordance with the received symbol sequence input from the carrier detector 2 and the symbol count supplied from the frame synchronizer 3. Thus, an MPEG2 transport stream is output.

  The television broadcast demodulator 1 has one configuration example as described above. Next, an example of a reception method according to the one configuration example will be described with reference to FIGS. 1 and 2.

<Processing outline of frame synchronization unit>
FIG. 3 is a flowchart illustrating a processing example of the frame synchronization unit 3.
In step S1, the detection flag is set to zero. Next, in step S2, the frame synchronization unit 3 waits for input of a symbol.

<Synchronous detection mode>
In the initial demodulation stage, the frame synchronization unit 3 operates in the synchronization detection mode. In the synchronization detection mode, a synchronization detection process is performed for each symbol (step S10). The synchronization detection process collectively detects the arrival of the synchronization signal and the ICFO value from the received symbol sequence. Details of this synchronization detection processing will be described later. In step S3, the synchronization detection process is continued for each symbol until synchronization is detected.

<Synchronous hold mode>
When a synchronization signal is detected in the synchronization detection process, the frame synchronization unit 3 performs a predetermined intermediate process (step S700) described later once after detection, and then shifts to the synchronization holding mode. The intermediate processing includes processing for feedback control of the carrier detection unit 2 based on the detected ICFO value. In step S4, the frame synchronization unit 3 waits for input of a symbol. In the synchronization holding mode, synchronization holding processing is performed for each symbol (step S800). The synchronization holding process appropriately updates the symbol count based on the input received symbol sequence.

<Synchronous detection processing>
FIG. 4 is a flowchart illustrating a procedure example of the synchronization detection process illustrated in FIG. In the following flowcharts, the symbol “←” indicates that the right side of the arrow is substituted for the left side.

In the differential demodulation process, the differential demodulation value and the carrier power value are calculated and stored in the buffer for each of the received N _FFT received carrier values (step S100).

  The subsequent three processes of TMCC demodulation processing (step S200), sync correlation calculation processing (step S300), and maximum correlation detection processing (step S400) are Nw “ICFO candidate values” (hereinafter referred to as “ICFO candidate values”). , Icfo candidate value) is performed only Nw times. Steps S110, S410, and S420 constitute a loop for sequentially performing the above-described three processes for these Nw icfo candidate values. That is, in step S110, the first icfo candidate value (−Nw / 2) is set to the variable i representing the icfo candidate value. In step S410, i is updated to the next icfo candidate value every time the above three processes are completed. In step S420, after confirming that the above three processes for all icfo candidate values have been completed, the loop is exited. By the loop described above, the above-described three processes are executed in the range of −Nw / 2 ≦ icfo candidate value <Nw / 2.

  The TMCC demodulation process performs a process corresponding to the icfo candidate value on the differential demodulated value and the carrier power value to calculate a TMCC demodulated value. The sync correlation calculation process performs a correlation calculation between the TMCC demodulated value sequence and the frame sync pattern, and calculates a soft correlation value and a hard correlation value. In the maximum correlation detection process, the Nw soft correlation values calculated for each symbol have the maximum absolute value as a maximum likelihood soft correlation value, and an icfo candidate value that gives the maximum likelihood soft correlation value is detected. As the maximum likelihood icfo value, the hard correlation value corresponding to the maximum likelihood icfo value is detected as the maximum likelihood hard correlation value. Details of the TMCC demodulation process, the sync correlation calculation process, and the maximum correlation calculation process will be described later.

  The high-speed detection process and the low-speed detection process detect the arrival of a synchronization signal based on the maximum likelihood soft correlation value, the maximum likelihood hard correlation value, and the maximum likelihood icfo value, respectively. Note that the maximum likelihood icfo candidate value at the time when the arrival of the synchronization signal is detected is adopted as the detected ICFO value. Details of these high-speed detection processing and low-speed detection processing will be described later.

FIG. 5 is a flowchart illustrating a procedure example of the differential demodulation processing illustrated in FIG.
The differential demodulation process is performed on the range of 0 ≦ q <N _FFT , that is, all carriers in the symbol (steps S101, S105, and S106). Here, q is a variable (carrier index) indicating the carrier position in the symbol. In step S102, differential demodulation is performed by multiplying the current carrier value by the complex conjugate value of the carrier value one symbol before, and the resulting differential demodulation value is stored in the buffer memory d [q]. Yes. Here, x (q) represents the qth received carrier value supplied from the carrier detector. As will be described later, the reception carrier value of one symbol before is stored in X [q]. The symbol ( ^* ) is a complex conjugate operator. Differential demodulation cancels differential encoding and eliminates the influence of static transmission path characteristics for TMCC symbols modulated by DBPSK.

  In step S103, the power value of the carrier value is calculated and stored in the buffer memory e [q]. In step S104, the current carrier value necessary for processing with the next symbol is stored in the memory X [q].

  Before describing the details of the TMCC demodulation processing, the effect of ICFO on the received symbols will be described. First, the ICFO deviates the position of the received carrier by the ICFO value in the positive frequency direction. The ICFO rotates the phase of the received carrier value by a certain amount for each symbol, specifically, an amount obtained by multiplying the guard interval ratio by the ICFO value. The TMCC demodulation process demodulates the TMCC carrier by correcting the influence of these ICFOs on the assumption that the icfo candidate values are correct ICFO values.

  FIG. 6 is a flowchart illustrating a procedure example of the TMCC demodulation process illustrated in FIG.

  In step S204, the carrier index corresponding to the TMCC carrier is calculated in consideration of the carrier position deviation due to ICFO. Here, it is assumed that Nz carrier indexes corresponding to TMCC carriers when ICFO is zero are stored in the memory Z [] in advance. In step S205, the differential demodulated value corresponding to the calculated carrier index is read from the buffer memory and added to the variable D. If reference is made to the loop for the variable k configured in step S203, step S207 and step S208 and the initialization of the variable D in step S201, the variable D includes a TMCC carrier at the time of leaving the loop, that is, immediately before step 209. It will be understood that the total sum of the Nz differential demodulated values corresponding to is calculated. This total addition reduces the influence of noise.

  Similarly, referring to step S202 and step S206, it will be understood that the total addition of Nz carrier power values corresponding to the TMCC carrier is calculated for the variable E.

  In step S209, the above-described phase rotation by ICFO is corrected. Here, G is a guard interval ratio. In the illustrated symbols, the symbol “j” represents an imaginary unit, exp () represents a complex exponential function, and “real ()” represents taking a real part. After all, it should be noted that it is not necessary to calculate the imaginary part in the calculation of step S209. In step S210, the phase-corrected value is normalized by dividing by the total power added value, and the TMCC demodulated value is calculated.

  FIGS. 7A to 7C and FIGS. 8A to 8C exemplify TMCC demodulated value sequences obtained by simulation, respectively. In this simulation, the ICFO value is 3. 7A to 7C and FIGS. 8A to 8C, the horizontal axis indicates the symbol index p, and the vertical axis indicates the TMCC demodulated value.

  FIG. 7A to FIG. 7C illustrate TMCC demodulated value sequences corresponding to correct icfo candidate values, respectively, and FIG. 8A to FIG. 8C respectively show incorrect icfo candidate values. The corresponding TMCC demodulated value series is illustrated.

  As shown in FIG. 7A, when the reception C / N is high, the TMCC demodulation value corresponding to the correct icfo candidate value is very close to either +1 or -1. It is clear that the transmitted TMCC bits are correctly reproduced by performing a binary decision on the TMCC demodulated sequence corresponding to the correct icfo candidate value with 0 as a boundary.

  Referring to FIG. 7B, it can be seen that the validity of the binary determination is extremely high as long as a reception C / N of 0 dB or more is secured. On the other hand, as shown in FIGS. 8A to 8C, the absolute value of the TMCC demodulated value corresponding to the incorrect icfo candidate value is a small value regardless of the reception C / N. This is because the Nz differential demodulated values to be selectively added do not correspond to the TMCC carrier, and therefore their phases do not match.

  FIG. 9 is a flowchart illustrating a procedure example of the sync correlation calculation process. This process is a process for calculating the soft correlation value indicated by the symbol s and the hard correlation value indicated by the symbol h. In the flowchart, the memory represented by w [] contains a binary sequence {1, 1, -1, -1, 1, -1, 1, -1, -1,-corresponding to the sync word W0. 1, -1, 1, -1, -1, -1, 1} are stored in advance.

  Step S301, Step S304, and Step S307 form a loop that starts from the initial value 15 and decrements to 0 for the variable k. Referring to this loop and steps S302 and S305, at the end of the sync correlation calculation process, the variable s has a correlation value between the TMCC demodulated value sequence of the latest 16 symbols and a known 16-bit synchronization signal pattern, that is, a soft correlation. It will be understood that the value is calculated. In step S302, the product of the latest TMCC demodulated value T and W [15] is substituted for s, and in step S305, the product of the (15-k) symbol previous TMCC demodulated value and w [k] is 14≥ By sequentially adding to s in the range of k ≧ 0, the soft correlation value between the TMCC demodulated sequence of the last 16 symbols and the synchronization signal is finally calculated.

  The absolute value of the soft correlation value corresponding to the correct icfo candidate value becomes a large value as the frame sync arrives, and the sign is inverted for each frame.

  On the other hand, if attention is focused on the above-described loop and steps S303 and S306, at the end of the sync correlation calculation process, the variable h is a sequence obtained by performing a binary decision on the TMCC demodulated value sequence of the last 16 symbols and the synchronization signal pattern. It will be understood that a correlation value with, ie a hard correlation value, is calculated. The symbol “sgn (x)” represents x / | x | (assuming that sgn (0) = 0).

  The hard correlation value is 16 when the binary determination sequence completely matches the sync word W0, and becomes -16 when the binary determination sequence matches the sync word W1. Referring to the discussion on the validity of the binary determination described above, when the absolute value of the hard correlation value corresponding to the correct icfo candidate value is 16 in a reception C / N environment of 0 dB or more, frame sync It can be judged that has arrived.

  In step S308, the current TMCC demodulated value necessary for processing with the next symbol is stored in the memory. In this memory, Nw TMCC demodulated values calculated for each symbol are stored over a period of 15 symbols, so that the circuit scale becomes very large.

  Therefore, in this embodiment, an external memory is used as the memory. Specifically, the memory 4a of the main demodulator 4 that is not operating at this stage, for example, a transmission path estimation memory or a deinterleave memory is used. By using an external memory, an increase in circuit scale can be significantly suppressed.

  FIG. 10A to FIG. 10C and FIG. 11A to FIG. 11C are diagrams illustrating soft correlation value sequences obtained by simulation. FIG. 10 illustrates a soft correlation value sequence corresponding to a correct icfo candidate value, and FIG. 11 illustrates a soft correlation value sequence corresponding to an incorrect icfo candidate value. 10A to 10C and 11A to 11C, the horizontal axis indicates the symbol index p, and the vertical axis indicates the TMCC demodulated value.

  In FIG. 10, the soft correlation value corresponding to the arrival of the frame sync is indicated by a circle CM. As described above, it can be seen that the absolute values of these soft correlation values are large. On the other hand, as shown in FIG. 11, the soft correlation value corresponding to the incorrect icfo candidate value is a small value regardless of the received C / N.

FIG. 12 is a flowchart illustrating an exemplary procedure of maximum correlation detection processing.
In the maximum correlation detection process, the Nw soft correlation values calculated for each symbol have the maximum absolute value as a maximum likelihood soft correlation value, and an icfo candidate value that gives the maximum likelihood soft correlation value is detected. As the maximum likelihood icfo value, the hard correlation value corresponding to the maximum likelihood icfo value is detected as the maximum likelihood hard correlation value.

  In the maximum correlation detection process, when i is the first candidate value (−Nw / 2), or when the soft correlation value s is larger than the maximum value S so far (step S401), three variables I, S, H is updated (steps S402, S403, and S404). Referring to this update process and the loop related to i in FIG. 4, immediately before the fast detection process (step S500), the variable S has the maximum likelihood soft correlation value, the variable I has the maximum likelihood icfo value, and the variable H It will be understood that the maximum likelihood hard correlation value is stored in each. FIG. 13A to FIG. 13C are diagrams illustrating the maximum likelihood soft correlation value series obtained by simulation. At this time, the necessity of the maximum correlation detection process is unclear. The effect of the maximum correlation detection process will be described in the description of the low speed detection process.

  FIG. 14 is a flowchart illustrating an example of a procedure of high-speed detection processing. Step S501 is provided in order not to perform substantial detection processing during the first 16 symbols. This is because the differential demodulation process requires a received carrier value of one symbol before, and the sync correlation calculation process requires TMCC demodulated values up to 15 symbols before, so the first 16 values are undefined. This is because a valid maximum likelihood soft correlation value, maximum likelihood hard correlation value, and maximum likelihood icfo value are not calculated for symbols.

  Steps S502 and S503 give the following soft correlation value conditions and hard correlation value conditions. The high-speed detection process detects the arrival of the frame sync when the maximum likelihood soft correlation value and the maximum likelihood hard correlation value satisfy these two conditions.

Soft correlation value condition) Absolute value of maximum likelihood soft correlation value must be greater than 4 (soft correlation threshold) Hard correlation value condition) Absolute value of maximum likelihood hard correlation value must be 16 (upper hard correlation value)

  The soft correlation value condition ensures the correctness of the detected ICFO value. As can be seen from FIG. 11, the absolute value of the soft correlation value corresponding to the incorrect icfo candidate value does not exceed 4 regardless of the magnitude of C / N. Therefore, if the threshold value of the soft decision condition is set to 4, it is guaranteed that no erroneous detection of the ICFO value occurs.

  Next, the role of the hard correlation value condition is clarified. In FIG. 13A, the maximum likelihood soft correlation value corresponding to the arrival of the frame sync is indicated by a circle CM. These correlation values naturally satisfy the soft correlation value condition. However, in addition to these correlation values, there are those having a relatively large absolute value and satisfying the soft correlation value condition, such as a correlation value indicated by a square box SM in the figure.

  When the hard correlation value condition does not exist, such a correlation value may cause erroneous detection of frame sync. In order to prevent such erroneous detection, the threshold value of the soft correlation value condition may be set to a large value such as 15, for example.

  However, with this method, when the reception C / N is low, that is, in the situation shown in FIG. 13B, there is a possibility that the correlation value corresponding to the frame sync may be missed. In other words, it is difficult to solve the trade-off between the prevention of erroneous detection at high C / N and the securing of detectability at low C / N only by the soft correlation value condition.

  In the high-speed detection processing in the present embodiment, this trade-off is solved by providing a hard correlation value condition in addition to the soft correlation value condition. In other words, by adopting a low value for the threshold value of the soft correlation value condition, the detectability at low C / N is ensured, and the presence of the hard correlation value condition prevents false detection at high C / N. It is.

  It should be emphasized here that the fast detection process can immediately detect the arrival of the frame sync. As long as a certain amount of reception C / N is ensured, the high-speed detection process can detect immediately without missing the arrival of the frame sync. In the high-speed detection process, when a pattern identical to the frame sync, that is, a so-called pseudo frame sync, exists in the TMCC sequence, it is erroneously recognized as a frame sync and detected. This problem regarding erroneous detection is solved in a frame synchronization holding process to be described later.

  As described above, the high-speed detection process can immediately detect the arrival of the frame sync. However, as shown in FIG. 13C, in an environment where the reception C / N is very low, the high-speed detection process cannot detect the arrival of the frame sync. In this case, the absolute value of the maximum likelihood soft correlation value is always a small value, and the soft correlation value condition is not satisfied no matter how long it waits. The low-speed detection process is provided so that the arrival of the frame sync can be reliably detected even in such a case.

FIG. 15 is a diagram illustrating a procedure example of the low speed detection process.
Step S601 is provided so that substantial detection processing is not performed for a period of 204 symbols in addition to the first 16 symbols. This is because, as will be described later, the low-speed frame synchronization detection process requires the maximum likelihood soft correlation value and the maximum likelihood icfo value for the past one frame period.

  In step S602, it is confirmed that the current likelihood and the maximum likelihood icfo value 204 symbols before are equal. In step S603, it is confirmed that the sign is inverted between the current and the maximum likelihood soft correlation value 204 symbols before. In steps S604 to S608, it is confirmed that all of the maximum likelihood soft correlation values of the past 203 symbols are smaller in absolute value than the maximum likelihood soft correlation values of the current and 204 symbols before. The low-speed frame detection process detects the arrival of a frame sync when all the above three conditions are satisfied (step S609). In step S610, the current maximum likelihood soft correlation value necessary for processing with the next symbol is stored in the memory. Similarly, in step S611, the maximum likelihood icfo value is stored in the memory.

  Here, the necessity of the maximum correlation detection process will be clarified. In fact, if frame sync detection in an environment where the reception C / N is very low is not important for the receiver, that is, if only high-speed detection processing is sufficient, there is no need for maximum correlation detection processing. In that case, the maximum correlation detection process is eliminated, and in the high-speed detection process, it is checked whether a soft correlation value satisfying the soft correlation value condition exists among Nw soft correlation values. After confirming that the hard correlation value paired with the hard correlation value satisfies the hard correlation value condition, the arrival of the frame sync is detected, and the ICFO candidate value that gives the soft correlation value is used as the detected ICFO value. With this configuration, the preferable characteristics described so far, that is, the validity of the detected ICFO value and the validity of the frame sync detection are not lost. This is because these preferable characteristics are attributed to the properties of the soft correlation value and the hard correlation value, and are not derived from the properties specific to the maximum likelihood soft correlation value and the maximum likelihood hard correlation value.

  In contrast to the high-speed detection process, the maximum correlation detection process is very important for the low-speed detection process. As in the case of the high-speed detection process, the process for the Nw soft correlation values can be performed for the low-speed detection process. However, as described above, the low-speed detection process requires information regarding the current and 204 symbols before the soft correlation value. Therefore, when there is no maximum correlation detection process and all the Nw soft correlation values are processed by the low speed detection process, there is a huge memory that can store Nw soft correlation values over 204 symbol periods. It becomes necessary and is not preferable. In short, the maximum correlation detection process has the effect of greatly reducing the amount of memory required for the low-speed detection process.

<Intermediate processing>
FIG. 16 is a flowchart illustrating a procedure example of the intermediate process illustrated in FIG. 3.
In the intermediate processing, first, feedback control for the carrier detection unit 2 is performed based on the detected ICFO value (step S700a). In S701, TMCC demodulated values t [I] [0] to t [I] [14] corresponding to the detected ICFO values are obtained from the memory 4a of the main demodulator 4 that has been used for storing the TMCC demodulated values in the sync correlation processing. The data is read and copied to the internal memories m [0] to m [14].

  Steps S702 to S707 are all preparations for a synchronization holding process to be described later. In step S702, the maximum likelihood soft correlation value is stored in the buffer memory. In steps S703 to S706, variables used in the synchronization holding process described later are initialized. In step S707, the symbol count sym is initialized to 1.

<Synchronous hold processing>
FIG. 17 is a flowchart illustrating a procedure example of the synchronization holding process illustrated in FIG. In the illustrated flowchart, the symbol “%” indicates a remainder obtained by division. For example, “n% m” indicates a remainder obtained by dividing the variable n by the variable m.

  First, in step S750, differential demodulation processing is performed. The subsequent steady TMCC demodulation processing (step S900) and steady sync correlation calculation processing (step S1000) are performed only once for each symbol, unlike the case of the synchronization detection processing described above.

  As shown in FIG. 18, the steady TMCC demodulation process performs exactly the same process as the TMCC demodulation process when the icfo candidate value is 0. Except for the above points, the steady TMCC demodulation process is substantially the same as the TMCC demodulation process, and thus the description thereof is omitted.

  As shown in FIG. 19, the steady sync correlation calculation process is substantially the same as the sync correlation calculation process except for the following two differences. The first difference is that a hard correlation value is not calculated. The second difference is that instead of using the memory 4a of the main demodulator 4, an internal memory (register) is used as a memory for storing the TMCC demodulated value. Except for the above points, the steady sync correlation calculation process is the same as the sync correlation calculation process, and a description thereof will be omitted.

  First, step S801 is provided in order not to perform processing from step S802 to offset update processing (S1100) in the first one frame period. This is because the soft correlation value one frame before is indefinite during this period.

  The processing in steps S802 to S805 is controlled by a local counter value cnt that is incremented for each symbol from 0 to 203. In step S802, the interframe differential correlation value Y is calculated by subtracting the soft correlation value L [0] one frame before from the current soft correlation value s. The absolute value | Y | of the inter-frame difference correlation value Y shows a large peak for each frame in accordance with the arrival of the frame sync. Steps S803 to S805 are processes for detecting the position of this peak in the frame. Here, it should be noted that no peak is observed for the pseudo frame sync. This is because the influence of TMCC data other than the frame sync is eliminated by taking the inter-frame difference.

  In steps S803 and S804, when | Y | is larger than variable maxY (and when the local counter is 0), maxY is updated to | Y |, and the local counter value at that time is substituted into variable maxC. ing. By the above processing, immediately before the offset update processing (step S1100), it is clear that the peak value in the last 204 symbols is stored in the variable maxY, and the local counter value in which the peak is observed is stored in the variable maxC. I will.

  In the offset update process (step S1100), the head symbol offset value ofs is updated for each frame based on the detected peak position (maxC) (see FIG. 20). In the offset update process, when the detected peak position is the same value continuously for a predetermined number of times (for example, twice), the head symbol offset value is updated to the detected peak position.

  In step S806, the soft correlation value s is stored in the memory L [0: 203] in preparation for processing at the next symbol time point. In step S807, the local counter value cnt is updated. In step S808, the symbol counter value sym is calculated from the head symbol offset value ofs and the local counter value cnt.

  As described above, the receiving apparatus 1 in the present embodiment receives an OFDM signal whose transmission unit is an OFDM symbol composed of a plurality of carriers, and decodes the transmitted main information sequence. A signal is composed of a fixed number of OFDM symbols that are continuous in time to form one OFDM frame, and control information including a synchronization signal having a predetermined number of bits is transmitted for each OFDM frame by one or more specific carriers of the OFDM symbol. Carrier detection means 2 (carrier detection unit) that detects the received OFDM signal and outputs a reception symbol composed of a plurality of reception carrier values, and processes according to different frequency deviation values. Is performed on the received symbol sequence to detect the arrival of the synchronization signal for each symbol. A number of synchronization detection means 3 (frame synchronization units), the symbol time point at which one of the synchronization detection means 3 detects the arrival of the synchronization signal, and the synchronization detection means 3 that detected the synchronization signal at this time correspond to each other The main information sequence is decoded from the OFDM signal according to the frequency deviation value to be performed.

  The receiving method in the above embodiment is a receiving method for receiving an OFDM signal whose transmission unit is an OFDM symbol composed of a plurality of carriers, and decoding the transmitted main information sequence. The OFDM signal is constant in time. A number of OFDM symbols constitute one OFDM frame, and control information including a predetermined number of bits of synchronization signal is transmitted for each OFDM frame by one or more specific carriers of the OFDM symbol, and received. A carrier detection step of detecting the OFDM signal and outputting a reception symbol comprising a plurality of reception carrier values, and performing a process corresponding to a different frequency deviation value on the series of the reception symbols, and A plurality of synchronization detection steps for detecting the arrival of a signal for each symbol, and The main information sequence is decoded from the OFDM signal according to the symbol time at which one of the period detection steps detects the arrival of the synchronization signal and the frequency deviation value corresponding to the synchronization detection step at which the synchronization signal is detected at this time. It is characterized by performing.

  By doing so, a process (ICFO detection process) for detecting the carrier frequency deviation of the received symbol sequence is executed simultaneously with the frame synchronization process for detecting the synchronization signal (frame sync) from the received symbol sequence. Become so. For this reason, it is not necessary to follow the procedure of detecting the synchronization signal from the series of received symbols after detecting the carrier frequency deviation. Therefore, the time until detection of frame synchronization can be shortened.

  In the receiving apparatus 1 in the above embodiment, in addition to the above-described configuration, the synchronization detecting unit 3 further extracts and extracts a reception carrier value corresponding to the control information transmission carrier from a reception symbol according to the frequency deviation value. A control information demodulating means for calculating a control information demodulated value by performing processing according to the frequency deviation value on the received carrier value, and performing a correlation operation between the sequence of the control information demodulated value and the synchronization signal Soft correlation calculation means for calculating a soft correlation value, and detecting arrival of the synchronization signal based on the soft correlation value.

  In addition to the configuration described above, the receiver 1 in the above embodiment further performs a correlation operation between the synchronization signal and the sequence obtained by performing binary determination on the control information demodulated value, Hard correlation calculating means for calculating a hard correlation value is provided, and a synchronization signal is detected based on the hard correlation value.

  In addition to the above-described configuration, the receiver 1 in the embodiment further includes the synchronization detection unit 3 in which the soft correlation value satisfies a predetermined soft correlation value condition and the hard correlation value is a predetermined hard correlation value condition. When the condition is satisfied, the arrival of the synchronization signal is detected.

  In this way, the synchronization detection means 3 can immediately detect the arrival of the synchronization signal.

  In addition to the above-described configuration, the receiving device 1 in the embodiment further includes the soft correlation value condition as a necessary condition that an absolute value of the soft correlation value is larger than a predetermined soft correlation threshold, and the hard correlation value The condition includes that the absolute value of the hard correlation value is equal to the upper limit hard correlation value as a necessary condition.

  As described above, the receiving apparatus 1 in the above embodiment receives the OFDM signal whose transmission unit is an OFDM symbol composed of a plurality of carriers. In the receiving apparatus 1, the OFDM signal is a certain number of OFDM symbols continuous in time. The control information including a synchronization signal having a predetermined number of bits is transmitted for each OFDM frame by one or more specific carriers of the OFDM symbol, and the received OFDM signal is Carrier detection means 2 (carrier detection unit) for detecting and outputting a reception symbol composed of a plurality of reception carrier values, each performing a process corresponding to a different frequency deviation value on the series of reception symbols, A plurality of correlation calculating means for outputting soft correlation values and hard correlation values, and a plurality of correlation calculation means for each symbol Outputs one soft correlation value satisfying a predetermined selection condition among the soft correlation values as the maximum likelihood soft correlation value, and the frequency deviation value corresponding to the correlation calculation means that outputs the maximum likelihood soft correlation value as the maximum likelihood frequency deviation Based on the maximum likelihood soft correlation value and the maximum likelihood hard correlation value, the maximum correlation detection means for outputting the hard correlation value output by the correlation calculation means that has calculated the maximum likelihood soft correlation value as the maximum likelihood hard correlation value. Synchronization detection means 3 (frame synchronization section) for detecting the arrival of the synchronization signal, a symbol time point at which the synchronization detection means 3 detects the arrival of the synchronization signal, and a maximum likelihood frequency deviation value at that time point, The main information sequence is demodulated from the OFDM signal according to the above.

  In this way, the synchronization detection means 3 can immediately detect the arrival of the synchronization signal.

  In the receiving apparatus 1 in the above embodiment, in addition to the above-described configuration, the correlation calculating unit further extracts a received carrier value corresponding to the control information transmission carrier from a received symbol according to the frequency deviation value. A control information demodulating means for calculating a control information demodulated value by performing processing according to the frequency deviation value on the received carrier value, and performing a correlation operation between the control information demodulated value sequence and the synchronization signal. The soft correlation value is calculated, and the hard correlation value is calculated by performing a correlation operation between a sequence obtained by binary determination of the control information demodulated value and the synchronization signal.

  In addition to the configuration described above, the receiving apparatus 1 in the above embodiment further includes that the soft correlation value selection condition includes a maximum condition among a plurality of soft correlation values calculated for each symbol as a necessary condition. Features.

  In addition to the configuration described above, the receiving apparatus 1 in the above embodiment further requires that the soft correlation value selection condition is that the absolute value is the maximum among a plurality of soft correlation values calculated for each symbol. It is characterized by including.

  In addition to the configuration described above, the receiver 1 in the embodiment further includes the synchronization detection unit 3 in which the maximum likelihood soft correlation value satisfies a predetermined soft correlation value condition and the maximum likelihood hard correlation value is a predetermined value. When the hard correlation value condition is satisfied, the arrival of the synchronization signal is detected.

  In the receiving apparatus according to the embodiment, in addition to the configuration described above, the soft correlation value condition further includes that the absolute value of the maximum likelihood soft correlation value is larger than a predetermined soft correlation threshold as a necessary condition, and the hard correlation The value condition includes that the absolute value of the hard correlation value is equal to the upper limit hard correlation value as a necessary condition.

  In addition, this embodiment is not restricted above, A various deformation | transformation is possible. Hereinafter, such modifications will be described in order.

  In the above embodiment, when the power of the reception carrier is maintained at a constant value by AGC or the like, the power is not calculated in the differential demodulation process, and may be replaced with the expected power value PWR of the TMCC carrier. good. Specifically, “E” in the denominator on the right side in step S210 in FIG. 6 may be changed to “PWR”. Accordingly, E need not be calculated, and therefore step S103 in FIG. 5 or step S206 in FIG. 6 and step S906 in FIG. 18 can be omitted.

In the case of further modification in the present embodiment, the division itself of step S210 and step S909 may be omitted, and the soft correlation value condition may be set to the following soft correlation value condition a.
Soft correlation value condition a) The absolute value of the maximum likelihood soft correlation value is larger than 4 × N _Z × PWR

  In the above embodiment, when it is not necessary to establish synchronization in an environment where the C / N is very low, the low speed detection process (step S600) can be omitted.

  In the above embodiment, the hard correlation value may not be calculated as described above, and only the coincidence between the binary determination sequence of the TMCC demodulation sequence and the frame sync pattern may be detected. That is, it may be detected only that the hard correlation value is +16 (upper hard correlation value) or -16 (lower hard correlation value).

  In addition to those already described above, the methods according to the above-described embodiments and modifications may be used in appropriate combination.

It is a whole block diagram of the demodulator for ISDB-T television broadcasting by this embodiment. It is a figure which shows an example of a parameter specification. It is a flowchart which shows the process example of a frame synchronizer. It is a flowchart which shows the example of a procedure of the synchronous detection process shown in FIG. 5 is a flowchart illustrating an example of a procedure of differential demodulation processing illustrated in FIG. 5 is a flowchart showing an example of a procedure of TMCC demodulation processing shown in FIG. It is a figure which shows an example of the TMCC demodulation value series obtained by simulation. It is a figure which shows an example of the TMCC demodulation value series obtained by simulation. It is a flowchart which shows the example of a procedure of a sync correlation calculation process. It is a figure which shows an example of the TMCC demodulation value series obtained by simulation. It is a figure which shows an example of the TMCC demodulation value series obtained by simulation. It is a flowchart which shows the example of a procedure of the maximum correlation detection process shown in FIG. It is a figure which shows an example of the TMCC demodulation value series obtained by simulation. It is a flowchart which shows the example of a procedure of the high-speed detection process shown in FIG. It is a figure which shows the example of a procedure of the low speed detection process shown in FIG. 4 is a flowchart illustrating an exemplary procedure of intermediate processing illustrated in FIG. 3. 4 is a flowchart illustrating a procedure example of synchronization holding processing illustrated in FIG. 3. It is a flowchart which shows the example of a procedure of steady TMCC demodulation processing. It is a flowchart which shows the example of a procedure of a stationary sync correlation calculation process. It is a flowchart which shows the example of a procedure of an offset update process.

Explanation of symbols

1 Demodulator for TV broadcasting (receiver)
2 Carrier detection unit (carrier detection means)
3 Frame synchronization unit (synchronization detection means)
4 Main demodulator 4a Memory S502 Soft correlation value condition S503 Hard correlation value condition sym Symbol count

Claims (10)

In a receiving apparatus that receives an OFDM signal having an OFDM symbol composed of a plurality of carriers as a transmission unit and decodes the transmitted main information sequence,
The OFDM signal constitutes one OFDM frame with a certain number of OFDM symbols continuous in time,
Control information including a synchronization signal of a predetermined number of bits is continuously transmitted for each OFDM frame by one or more specific carriers of the OFDM symbol,
Carrier detection means for detecting the received OFDM signal and outputting a reception symbol comprising a plurality of reception carrier values;
A plurality of synchronization detection means for detecting the arrival of the synchronization signal for each symbol by performing processing corresponding to different frequency deviation values on the received symbol series,
A receiver for Ru provided with,
The synchronization detection means includes
A received carrier value corresponding to the control information transmission carrier is extracted from a received symbol according to the frequency deviation value, and a process according to the frequency deviation value is performed on the extracted received carrier value to obtain a control information demodulated value. Control information demodulation means for calculating;
Soft correlation calculating means for calculating a soft correlation value by performing a correlation operation between the control information demodulated value sequence and the synchronization signal;
With
A symbol time point at which one of the synchronization detection means detects the arrival of the synchronization signal based on the soft correlation value, and a frequency deviation value corresponding to the synchronization detection means detecting the synchronization signal at this time;
And receiving the main information sequence from the OFDM signal. The receiving device according to claim 1 ,
The synchronization detection means includes
A hard correlation calculating means for calculating a hard correlation value by performing a correlation operation between a sequence obtained by binary determination of the control information demodulated value and the synchronization signal;
A receiving apparatus that detects a synchronization signal based on the hard correlation value. The receiving device according to claim 2 ,
The synchronization detection means includes
The soft correlation value satisfies a predetermined soft correlation value condition,
And when the hard correlation value satisfies a predetermined hard correlation value condition,
A receiving apparatus for detecting arrival of a synchronization signal. The receiving apparatus according to claim 3 ,
The soft correlation value condition includes that the absolute value of the soft correlation value is larger than a predetermined soft correlation threshold as a necessary condition,
The hard correlation value condition includes, as a necessary condition, that the absolute value of the hard correlation value is equal to an upper limit hard correlation value. In a receiving apparatus that receives an OFDM signal whose transmission unit is an OFDM symbol composed of a plurality of carriers,
The OFDM signal constitutes one OFDM frame with a certain number of OFDM symbols continuous in time,
Control information including a synchronization signal of a predetermined number of bits is continuously transmitted for each OFDM frame by one or more specific carriers of the OFDM symbol,
Carrier detection means for detecting the received OFDM signal and outputting a reception symbol comprising a plurality of reception carrier values;
A plurality of correlation calculating means each for performing a process according to a frequency deviation value different from each other on the received symbol sequence and outputting a soft correlation value and a hard correlation value;
One soft correlation value that satisfies a predetermined selection condition among a plurality of soft correlation values calculated for each symbol is output as a maximum likelihood soft correlation value, and corresponds to a correlation calculation unit that outputs the maximum likelihood soft correlation value. Maximum correlation detection means for outputting a hard correlation value output as a maximum likelihood hard correlation value by using a frequency deviation value as a maximum likelihood frequency deviation value and a correlation calculation means for calculating a maximum likelihood soft correlation value;
Synchronization detection means for detecting arrival of a synchronization signal based on the maximum likelihood soft correlation value and the maximum likelihood hard correlation value;
A receiver for Ru provided with,
The correlation calculating means includes
A received carrier value corresponding to the control information transmission carrier is extracted from a received symbol according to the frequency deviation value, and a process according to the frequency deviation value is performed on the extracted received carrier value to obtain a control information demodulated value. Control information demodulation means for calculating;
Soft correlation calculation means for calculating the soft correlation value by performing a correlation operation between the control information demodulated value series and the synchronization signal;
A hard correlation value calculating means for calculating the hard correlation value by performing a correlation operation between a sequence obtained by binary determination of the control information demodulated value and the synchronization signal;
With
A symbol time point at which the synchronization detection means detects the arrival of the synchronization signal; and
Maximum likelihood frequency deviation value at that time,
And receiving the main information sequence from the OFDM signal. The receiving device according to claim 5 , wherein
The soft correlation value selection condition is:
A receiving apparatus characterized by including, as a necessary condition, a maximum value among a plurality of soft correlation values calculated for each symbol. The receiving device according to claim 5 , wherein
The soft correlation value selection condition is:
A receiving apparatus including a necessary condition that the absolute value is the maximum among a plurality of soft correlation values calculated for each symbol. The receiving device according to any one of claims 5 to 7 ,
The synchronization detection means includes
The maximum likelihood soft correlation value satisfies a predetermined soft correlation value condition;
And when the maximum likelihood hard correlation value satisfies a predetermined hard correlation value condition,
A receiving apparatus for detecting arrival of a synchronization signal. The receiving device according to claim 8 , wherein
The soft correlation value condition includes, as a necessary condition, that the absolute value of the maximum likelihood soft correlation value is larger than a predetermined soft correlation threshold,
The hard correlation value condition includes, as a necessary condition, that the absolute value of the hard correlation value is equal to an upper limit hard correlation value. In a receiving method for receiving an OFDM signal having an OFDM symbol composed of a plurality of carriers as a transmission unit and decoding the transmitted main information sequence,
The OFDM signal constitutes one OFDM frame with a certain number of OFDM symbols continuous in time,
Control information including a synchronization signal of a predetermined number of bits is continuously transmitted for each OFDM frame by one or more specific carriers of the OFDM symbol,
A carrier detection step of detecting the received OFDM signal and outputting a reception symbol comprising a plurality of reception carrier values;
A plurality of synchronization detection steps for detecting the arrival of the synchronization signal for each symbol by performing processing corresponding to different frequency deviation values on each of the received symbol sequences;
A receiving method of Ru with a
The synchronization detection step includes:
A received carrier value corresponding to the control information transmission carrier is extracted from a received symbol according to the frequency deviation value, and a process according to the frequency deviation value is performed on the extracted received carrier value to obtain a control information demodulated value. A control information demodulation step to calculate;
A soft correlation calculation step of calculating a soft correlation value by performing a correlation operation between the control information demodulated value sequence and the synchronization signal;
With
A symbol time at which any of the synchronization detection steps detects the arrival of the synchronization signal based on the soft correlation value ;
At this time, the frequency deviation value corresponding to the synchronization detection step that detected the synchronization signal,
And receiving the main information sequence from the OFDM signal.

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