JP2975937B1 - Error correction device - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To perform error correction for each layer without being affected by a layer having a bad error. SOLUTION: An OFDM signal input to a demodulation device 11 is input to an error correction device 12 after data of each carrier is demodulated for each layer by FFT processing or the like. In the error correction apparatus 12, while the timing of the input data of each layer is sequentially adjusted by the buffer unit 121, the output is input to the correction processing unit 122, and the error correction processing that matches the modulation and coding scheme of the layer is performed. I do. In addition, interference detection unit 1
23, the interference level of the data of each layer is detected, and the determination unit 124 determines whether or not the correction is possible at the reception level based on the interference level of each layer and the layer information. Is controlled to stop the correction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a receiving apparatus for receiving a digital broadcast signal by a plurality of hierarchically multiplexed modulation systems and coding systems, and corrects an error in a transmission line error of received and demodulated data. It relates to a correction device.

[0002]

2. Description of the Related Art As a next-generation digital broadcasting system,
The development of digital terrestrial broadcasting using the TV band by the current terrestrial wave is being promoted. The transmission method is O
A scheme using FDM (Orthogonal Frequency Division Multiplexing) has already been adopted as a European standard scheme, and is considered to be a leading scheme in Japan.

[0003] In a digital broadcasting transmission system using OFDM, convolutional coding-Viterbi decoding and Reed-Solomon (hereinafter, RS) are used to digitally modulate a majority carrier forming an OFDM signal and further reduce transmission path errors. A so-called concatenated code obtained by combining codes is used.

The terrestrial digital broadcasting transmission system in Japan, which is currently being discussed by the Telecommunications Technology Council, uses 6M
The Hz band is divided into 13 segments, and each segment has a structure in which an arbitrary modulation method and coding rate can be selected. Up to 4 combinations of modulation scheme and coding rate
Segments that can be up to the type and belong to the same combination are called a hierarchy.

The purpose of devising such a hierarchical division transmission system is mainly to select a transmission parameter according to a reception mode. For example, the layer for fixed reception is set to 64QAM and the coding rate is 7/8 with emphasis on the information transmission speed, and the layer for mobile reception is DQPSK, code capable of receiving in a poor propagation environment such as fading. Conversion rate 2 /
A combination of layers such as 3 is possible.

In OFDM, signals having different transmission systems (modulation systems and coding rates) are multiplexed on a plurality of layers and transmitted, and when a general-purpose decoder is to be shared between layers, the coding rate is reduced. The higher the system, the more the C / N transmission characteristics deteriorate. In particular, when a concatenated code that is continuous in time series such as a convolutional code-RS (Reed-Solomon) code is employed, the decoding operation is trace-backed (Viterbi decoding in which processing is performed in a direction returning on the time axis). If the general-purpose decoder is operated by time-division multiplexing in order to perform processing, etc., there is a problem that an error in a layer having a bad error propagates to a layer having a good error.

[0007] For example, as shown in FIG.
In the case of transmission by 6QAM, 16QAM in 64QAM
Even under the transmission condition where an error does not originally occur in 16QAM, error propagation occurs due to time-division multiplexing with 64QAM because transmission error is weaker.

[0008]

In a receiving apparatus for receiving a digital broadcast signal based on a plurality of types of modulation schemes and coding schemes hierarchically multiplexed as described above, a general-purpose decoder may be shared between layers. In this case, the higher the coding rate, the more the C / N transmission characteristic deteriorates, and there is a problem that errors in a layer having a bad error propagate to a layer having a good error.

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems, and to share a general-purpose decoder between layers in a receiving apparatus for receiving a digital broadcast signal using a plurality of hierarchically multiplexed modulation systems and encoding systems. Even in such a case, an object of the present invention is to provide an error correction device capable of performing error correction processing of each layer without being affected by a layer having a bad error.

[0010]

In order to solve the above problems, an error correction device according to the present invention has the following characteristic configuration.

(1) A plurality of hierarchically multiplexed modulation schemes,
An error correction device used for a receiving device that receives a digital broadcast signal by an encoding method and that corrects a transmission path error of received and demodulated data detects an interference component included in the received and demodulated data and detects the interference. A disturbance detection unit for determining a level, a buffer unit for temporarily holding the received demodulated data, an error correction unit for performing error correction on data output from the buffer unit, and an interference detection unit. A determination unit for determining, for each layer, whether the signal can be received or cannot be received from the interference level and the layer information, and the error correction unit stops the error correction processing of the layer determined to be unreceivable by the determination unit. It is characterized by the following.

According to this configuration, when it is determined that reception is impossible from the interference level in the received signal and the hierarchy information, the processing of the error correction unit is stopped. It is possible to avoid affecting the correctable hierarchy.

(2) In the configuration of (1), the digital broadcast signal uses a combination of a plurality of encoding schemes, and accordingly, the error correction unit includes a plurality of stages corresponding to the respective encoding schemes. When arranging error correction circuits in order and performing error correction processing, the determination unit monitors occurrence of uncorrection in a subsequent error correction circuit, and determines that this layer is unreceivable when uncorrectable occurs. Features.

According to this configuration, even if the correction circuit in the preceding stage has already become uncorrectable and has a bad influence on the layer that can be corrected in the subsequent correction circuit, this is automatically detected, Since the first-stage correction circuit is stopped, the influence on the second-stage correction circuit can be eliminated.For example, even when a plurality of modulation schemes or coding schemes are time-division multiplexed, a scheme having poor characteristics is used. It is possible to prevent the characteristic degradation of the hierarchy in other systems due to (a system having a low error correction capability).

As a method of the interference detection unit, the interference level is calculated from a variance of the received and demodulated data.
It is conceivable to detect an analog signal disturbance occurring in a specific frequency band and determine a disturbance level using a pilot signal included in the digital broadcast signal.

Further, if the determination unit is provided with a hysteresis characteristic in which the determination level for determining that reception is not possible and the determination level for determining that reception is possible are different, if the interference level fluctuates with a certain width. However, since ON / OFF of the correction processing does not frequently occur, a stable operation can be provided.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS.

(First Embodiment) FIG. 1 is a block diagram showing a configuration of an OFDM receiving apparatus provided with an error correction apparatus according to a first embodiment. In FIG. 1, an OFDM signal received by an antenna system (not shown) is
After the data of each carrier is demodulated for each layer by T processing, deinterleave processing, etc., the error correction device 1 of the present invention
2 is input.

In the error correction device 12, while the data of each layer input is sequentially delayed for a predetermined time by the buffer unit 121, the output is input to the correction processing unit 122, and the modulation method and the encoding method of the layer are used. Perform matching error correction processing. The error correction processing includes Viterbi decoding, and here, a general-purpose Viterbi decoder is used. Also, the interference level of the data of each layer input by the interference detection unit 123 is detected, and the determination unit 124 corrects the reception level based on the interference level of each layer, the modulation method, and the layer information of the coding method. Is determined, and if it is determined that decoding is impossible, the correction processing unit 122 is controlled so as to stop the correction operation.

As shown in FIG. 2, the interference detection means of the interference detection unit 123 detects the received C / N (carrier / noise ratio) by measuring the variance of the received symbol from a representative point. In this case, since the C / N limit that can be corrected is determined from the modulation method and the encoding method, if it is determined that the C / N is uncorrectable, the Viterbi decoding operation is stopped for the corresponding layer, and the error is corrected. To prevent the propagation of

In starting terrestrial digital broadcasting, interference from existing analog TV signals becomes a problem. That is, when the spectrum is viewed as shown in FIG. 3, the OFDM reception signal has a video carrier and an audio carrier of the analog TV broadcast. Therefore, the interference detection unit 123
Then, the interference level of the analog TV signal is detected from the spectrum of the received signal, and the detection result is notified to the determination unit 124. The determination unit 124 determines whether or not the interference level is an uncorrectable level based on separately provided hierarchical information (modulation scheme and coding scheme), and stops the Viterbi decoding operation as in the case of C / N.

As shown in FIG. 4, a pilot signal for demodulation (continuous pilot, scatted pilot) is embedded in the OFDM signal.
This is used as a reference signal in demodulation. For this reason, since the modulation method is BPSK or the signal amplitude is large, it is stronger than the original information symbol. Thus, the level of the above-mentioned pilot signal is detected by the interference detection section 123 and is sent to the determination section 124 as the interference level. As a result, the interference characteristics of the transmission path can be determined better, and highly accurate interference detection and correction control can be performed.

Next, control of the interference level detection and correction operation will be described. The actual state of the transmission path does not take a constant value, but fluctuates to some extent. For this reason, if the interference level fluctuates near the threshold of the interference determination level, ON / OFF of the correction operation frequently occurs, which is not a desirable state for the receiving apparatus.

Therefore, as shown in FIG. 5, when the interference level gradually worsens, the correction is stopped when the frequency of occurrence of the uncorrectable case increases to some extent. Conversely, even when the disturbance gradually improves, the operation is started immediately after reaching a level where the correction can be completely completed without immediately entering the correction operation. By providing the hysteresis characteristic in this way, even when the interference level fluctuates with a certain width, ON / OFF of the correction processing does not frequently occur, so that a stable operation can be provided.

(Second Embodiment) FIG. 6 is a block diagram showing a configuration of an OFDM receiver having an error correction device according to a second embodiment. In FIG. 6, the same parts as those in FIG. 1 are denoted by the same reference numerals, and different parts will be described here.

The present embodiment has a configuration in which the correction processing unit 122 has two correction circuits 122a and 122b.
In a transmission system in digital terrestrial broadcasting, a method of combining a plurality of encoding systems for error correction and exhibiting higher performance, such as a convolutional code and an RS code, is used. In this case, if it is detected that the correction code cannot be corrected in the correction code at the subsequent stage, the correction code may have already become uncorrectable at the previous stage and may have an adverse effect on other correctable layers.

The present embodiment is intended to solve such a problem.
The processing state of b is monitored, and when it is detected that the correction circuit 122b cannot perform correction, the first-stage correction circuit 122a is stopped.

According to this structure, the correction circuit 122a in the preceding stage has already become uncorrectable, and the correction circuit
Even if the correctable layer 2b has an adverse effect, this is automatically detected and the correction circuit 122 of the first stage is automatically detected.
a is stopped, so that the correction circuit 1
It is possible to eliminate the influence on the 22b. For example, as shown in FIG. 7, even when a plurality of modulation schemes (or coding schemes) such as 64QAM and 16QAM are time-division multiplexed, a scheme with poor characteristics ( It is possible to prevent the characteristic degradation of the hierarchy in other systems due to the system having a low error correction capability).

Of course, here, 64QAM and 16QAM
Has been described, but the same modulation scheme (for example, QPS
K, etc.), different coding schemes R = 7/8 and R = 1/2 are also established. Furthermore, a combination of different modulation schemes and different coding rates is possible.

In this embodiment, as in the first embodiment, the interference detection method of the interference detection unit 123 is as follows.
Calculating the interference level from the variance of the received demodulated data, detecting analog signal interference occurring in a specific frequency band, detecting the interference level using a pilot signal included in a digital broadcast signal, You can take the approach. In addition, the determination unit 124 may have a hysteresis characteristic in which the determination level for determining that reception is not possible is different from the determination level for determining that reception is possible.

In addition, the present invention is not limited to the above embodiment, and it goes without saying that various modifications can be made.

[0032]

As described above, according to the present invention, when a general-purpose decoder is shared between hierarchies in a receiving apparatus for receiving a digital broadcast signal of a plurality of hierarchically multiplexed modulation schemes and encoding schemes. However, it is possible to provide an error correction device capable of performing error correction processing of each layer without being affected by the layer having a bad error.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an OFDM receiving device including an error correction device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of the embodiment;
The figure which shows the form of the operation | movement which measures the dispersion | variation from the representative point of the received symbol.

FIG. 3 In the embodiment, as interference detection means,
The figure which shows the form of the operation | movement which detects the disturbance from the existing analog TV signal.

FIG. 4 is a block diagram showing the configuration of the embodiment;
The figure which shows the form of the operation | movement which detects interference using the pilot signal for demodulation.

FIG. 5 is a diagram showing an embodiment in which the determination processing of the determination unit has hysteresis characteristics in the embodiment.

FIG. 6 is a block diagram showing a configuration of an OFDM receiver including an error correction device according to a second embodiment of the present invention.

FIG. 7 shows 64QAM and 16QA in the embodiment.
The figure which shows the mode of operation | movement in case the multiple modulation system by M is time division multiplexed.

FIG. 8 is a diagram showing a form of an error correction operation of the conventional OFDM receiver.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Demodulation device 12 ... Error correction device 121 ... Buffer part 122 ... Correction processing part 122a, 122b ... Correction circuit 123 ... Interference determination part 124 ... Correction processing part

Continuation of the front page (72) Inventor Hidenori Tsuboi 8-8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Pref. Toshiba Multimedia Technology Research Institute, Inc. (56) References JP-A-64-44644 (JP, A) Transmission method for fixed reception and mobile reception ~ ", STRL Open Lectures and Proceedings, NHK Engineering Services, May 22, 1998, p. 67-72 (58) Field surveyed (Int. Cl. ⁶ , DB name) H04L 11/00 H04L 1/00

Claims (6)

(57) [Claims] 1. An error correction apparatus for use in a receiving apparatus for receiving a digital broadcast signal of a plurality of hierarchically multiplexed modulation schemes and encoding schemes and for correcting a transmission path error of received and demodulated data. An interference detection unit that detects an interference component included in the demodulated data and determines the interference level; a buffer unit that temporarily holds the received demodulated data; and an error in the data output from the buffer unit. An error correction unit that performs correction; and a determination unit that determines receivable / unreceivable for each layer based on the interference level and the layer information obtained by the interference detection unit. An error correction apparatus, wherein error correction processing of a layer determined to be unreceivable by the method is stopped. 2. The digital broadcast signal according to claim 1, wherein said digital broadcast signal uses a combination of a plurality of coding systems, and said error correction unit arranges a plurality of stages of error correction circuits corresponding to the respective coding systems in order. 2. The error correction circuit according to claim 1, wherein when performing error correction processing, the determination unit monitors occurrence of uncorrectable error in a subsequent-stage error correction circuit, and determines that this layer is unreceivable when uncorrectable error occurs. 3. Error correction device. 3. The error correction device according to claim 1, wherein the interference detection unit calculates the interference level from a variance of the received and demodulated data. 4. The error correction device according to claim 1, wherein said interference detection unit detects analog signal interference occurring in a specific frequency band. 5. The error correction device according to claim 1, wherein the interference detection unit determines an interference level using a pilot signal included in the digital broadcast signal. 6. The error correction device according to claim 1, wherein the determination unit has a hysteresis characteristic in which a determination level for determining that reception is not possible and a determination level for determining that reception is possible are different values.