JP2002217860A - Digital signal receiving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital signal receiving device which corresponds to an OFDM system and which can use a demapping reference value of high accuracy. SOLUTION: A digital signal receiving device 2000 receives a signal to which time interleaving processing is performed and which is transmitted by varying a data modulation system for the respective groups of a plurality of segments in the respective symbols by the OFDM system. A reliability detecting part 118 detects the reliability of a pilot signal included in every segment. A demapping reference value calculating part 126 extracts the pilot signal satisfying prescribed reliability, according to reliability detection result and calculates a reference value on a constellation, corresponding to the modulation system on the basis of the average value. Pre-demapping processing parts 130 to 134 perform pre-demapping processing in accordance with the modulation system corresponding to each segment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal receiving apparatus for demodulating an OFDM signal used in digital broadcasting and the like.

[0002]

2. Description of the Related Art In recent years, OFDM (Orthogonal Frequency Division Multiplexing) has been used as a modulation method for transmitting a video signal or an audio signal, which is excellent in terms of high quality transmission and frequency utilization efficiency.
g) A scheme has been proposed.

[0003] The OFDM system is a modulation system in which a number of subcarriers are set up in a band of one channel. This is a modulation method that is effective in terrestrial digital television broadcasting and the like, because it is resistant to ghosts and can be resistant to selective fading by devising a data structure for error correction.

[0004] In the OFDM transmission, the following processing is performed. First, for example, an analog signal such as a television signal is converted into a digital signal, and MPEG (Moving Picture E)
xperts Group). Subsequently, the data signal is subjected to byte interleave and bit interleave processing in order to disperse the cause of error such as noise in the transmission path, and the data signal is subjected to QPSK (Quadrature Pha
se Shift Keying, 16QAM (Quadrature Amplitud)
e Modulation), and performs mapping according to a modulation method such as 64QAM. Furthermore, in order to disperse the cause of error occurrence in the transmission path such as fading and signal loss,
Perform time interleave and frequency interleave processing, perform IFFT (Inverse Fast Fourier Transform),
After the orthogonal modulation, the frequency is converted to an RF frequency and transmitted.

[0005] The data signal modulated by the OFDM method is
Demodulation is performed by processing in a procedure completely opposite to that of transmission.

FIG. 14 is a schematic block diagram showing the configuration of a conventional OFDM receiving apparatus 5000. The tuner 11 is provided with the RF signal captured by the antenna,
Downconverts the frequency of the specified channel,
Let it be a baseband signal. The analog / digital conversion circuit 12 converts an analog signal into a digital signal, and generates I-axis (real number) data and Q-axis (imaginary number) data using Hilbert transform or the like.

The FFT (Fast Fourier Transform) circuit 13
Fast Fourier transform is performed on each of the I-axis data and the Q-axis data, and the time-axis data is used as the frequency-axis data. The frequency deinterleave circuit 14 performs an inverse process of the frequency interleave performed to compensate for the loss of the specific frequency signal due to the reflection of radio waves or the like. The time deinterleave circuit 15 performs an inverse process of the time interleave performed for fading resistance.

The demapping circuit 16 demaps the data after the time deinterleaving from the I-axis data and the Q-axis data and performs 2-bit (QPSK) and 4-bit (1
6QAM) or 6-bit (64QAM) data. Bit deinterleave circuit 17 performs a reverse process of bit interleave performed to increase error resilience. The Viterbi decoding circuit 18 corrects an error while performing reverse processing of convolution performed between byte interleaving and bit interleaving. The byte deinterleave circuit 19 performs a reverse process of the byte interleave performed to increase error resilience similarly to the bit interleave. The RS (Reed-Solomon) decoding circuit 20 corrects an error while performing reverse processing of RS coding performed before byte interleaving.

[0009] The MPEG decoding circuit 21 performs inverse processing of compression by the MPEG system to expand data, and the digital / analog conversion circuit 22 converts a digital signal into an analog signal. Thus, the video signal and the audio signal before being modulated by the OFDM method are reproduced and output for reproducing the video and the audio.

As described above, interleaving is frequently used in the OFDM system. In order to perform deinterleaving, it is necessary to temporarily store data. For this purpose, the frequency deinterleaving circuit 14, the time deinterleaving circuit 15, the bit deinterleaving circuit 17, and the byte deinterleaving circuit 19 each have a memory. Have. However, of the four types of interleaving, the amount of data targeted by frequency interleaving and time interleaving is extremely large, and these deinterleaving require a large-capacity memory.

The frequency interleaving and the time interleaving have a great effect of dispersing the causes of errors in the transmission path and ensuring high-quality transmission. However, a large memory capacity required for deinterleaving results in a significant increase in the circuit configuration of the receiver, which hinders improvement in manufacturing efficiency and cost reduction.

Therefore, in a digital signal receiving apparatus for receiving a signal transmitted by using the OFDM scheme, such as terrestrial digital broadcasting, it is possible to reduce the memory capacity required for such interleaving processing. is necessary.

Further, conventionally, as a method of calculating a demapping reference value from a pilot signal for the demapping process performed by the demapping circuit 16, the following procedure can be generally used.

I) All pilot signals in one symbol are extracted and their values are sequentially added.

Ii) Thereafter, the result of addition is divided by the number of pilot signals in one symbol to calculate an average value of the pilot signals.

Iii) Finally, a reference value for demapping is calculated by multiplying this value by an appropriate coefficient.

[0017]

However, in the above-described method, when a pilot signal having a lower reliability than other pilot signals due to the influence of multipath, interference, noise, or the like, the pilot signal is not transmitted. There is a problem that the accuracy of the demapping reference value obtained by multiplying the average value by a constant may be deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the invention is to provide an OFDM system.
It is an object of the present invention to provide a digital signal receiving apparatus which can use an accurate value as a demapping reference value in a digital signal receiving apparatus which has received a signal transmitted by a system.

Another object of the present invention is to provide a digital signal receiving apparatus which receives a signal transmitted by the OFDM method, in which a memory capacity required for interleaving processing is suppressed and a high precision is used as a demapping reference value. An object of the present invention is to provide a digital signal receiving device capable of using values.

[0020]

In the present invention, the reliability of a pilot signal is determined based on the reliability information signal, and the average value of the pilot signal is calculated using the pilot signal determined to be reliable. By doing so, a more reliable average value of the pilot signal can be obtained, so that the accuracy of the demapping reference value obtained by multiplying the average value of the pilot signal by a constant can be improved. .

That is, the digital signal receiving apparatus according to the first aspect is a signal transmitted by the orthogonal frequency division multiplexing method on a frame basis, wherein the frame includes a plurality of symbols, and each symbol includes a guard interval. A digital signal receiving apparatus comprising: a plurality of segments that are valid data; and a signal that receives a signal transmitted with a variable data modulation scheme for each group of a plurality of segments in each symbol. Fast Fourier transform processing means for performing the transform processing, reliability detecting means for detecting the reliability of the pilot signal included in each segment based on the output of the fast Fourier transform processing means, and detection of the reliability detecting means According to the result, a pilot signal satisfying a predetermined reliability is extracted, and the extracted pilot signal is extracted. A reference value calculating means for calculating a reference value on a constellation corresponding to the modulation scheme based on the average value; and at least a constellation based on an output of the fast Fourier transform processing means, in accordance with the modulation scheme corresponding to each segment. Demapping processing means for outputting information indicating which reference value corresponds to the mapping, and decoding processing means for performing error correction by maximum likelihood decoding processing based on the output of the demapping processing means .

According to a second aspect of the present invention, there is provided a digital signal receiving apparatus.
In addition to the configuration of the digital signal receiving device according to claim 1,
The signal transmitted by the orthogonal frequency division multiplexing method has been subjected to time interleaving processing, and the digital signal receiving apparatus performs time deinterleaving processing, which is inverse conversion of time interleaving processing, based on the output of the demapping processing means. And a time deinterleave processing means for performing the time deinterleave processing to the decoding processing means.

According to a third aspect of the present invention, there is provided a digital signal receiving apparatus,
In addition to the configuration of the digital signal receiving device according to claim 1,
The signal transmitted by the orthogonal frequency division multiplexing method is subjected to time interleave processing, and the digital signal receiving apparatus performs time deinterleave processing which is an inverse transform of time interleave processing based on the output of the fast Fourier transform processing means. And a time deinterleave processing means to be provided to the demapping processing means.

According to a fourth aspect of the present invention, there is provided a digital signal receiving apparatus.
In addition to the configuration of the digital signal receiving device according to claim 2 or 3, the group of the plurality of segments includes a first group having a reference signal for reliability evaluation by the reliability detection unit, and a reliability detection unit. A second group having no reference signal for reliability evaluation in step (a), the reliability detection means adds reliability information to the first group, and the reference value calculation means A first average value calculating means for extracting a pilot signal satisfying a predetermined reliability based on the reliability information, and calculating an average value of the extracted pilot signals, With respect to a second value for calculating an average value of the extracted pilot signals.
Average calculation means.

[0025] The digital signal receiver according to claim 5 is
In addition to the configuration of the digital signal receiving device according to claim 4,
The first average value calculation means receives the output of the reliability determination means, and calculates an average value based on the reliability information. And division means for performing the division.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION
The details will be described below with reference to the drawings. In the following description, a terrestrial digital broadcast is taken as an example of a system for transmitting data using the OFDM method, and the digital signal receiving apparatus according to the present application is assumed to be a terrestrial digital broadcast receiver. explain.

[First Embodiment] [Data Structure of Digital Terrestrial Broadcasting] In the following, first,
As a premise for describing the configuration of a terrestrial digital broadcast receiver, a data structure of terrestrial digital broadcast will be described.

FIG. 1 is a conceptual diagram for explaining the structure of OFDM data received by a terrestrial digital broadcast receiver.

As shown in FIG. 1, one OFDM frame is composed of 204 OFDM symbols. OF
A DM symbol is composed of a valid data section and an invalid data section (guard interval, null carrier).

FIG. 2 is a diagram showing a configuration of the OFDM symbol shown in FIG. A valid data section in one OFDM symbol is a group of data (data segment).
OFDM segment with pilot signal added to
It is configured to be arranged individually.

According to the terrestrial digital broadcasting specifications, 13 segments can be divided into a maximum of three layers, and a modulation method can be designated for each layer.

FIG. 3 is a diagram for explaining the structure of one OFDM segment in more detail. As shown in FIG. 3, one OFDM segment includes n carriers from the 0th to the (n-1) th.

FIG. 4 is a diagram for explaining the mode dependence of the configuration of one OFDM segment.

Referring to FIG. 4, the number of carriers of a data signal, the number of carriers of a pilot signal and the like constituting one OFDM segment are determined for each mode, and are set so that the total number of carriers is n. ing.

For the modulation of the OFDM system, DQPSK (Di
fferential QPSK), QPSK, 16QAM, 64QA
There are four types of M, each with a different mapping method. The DQPSK method is called a differential modulation method, and the others are called synchronous modulation methods. Although the types and arrangement positions of pilot signals inserted into the data signal of the OFDM segment differ between the differential modulation scheme and the synchronous modulation scheme, the total number of pilot signals included in one OFDM segment is defined as shown in FIG. ing.

[Configuration of Digital Terrestrial Broadcasting Receiver 1000] Next, an example of a circuit configuration of the digital terrestrial broadcasting receiver will be described.

FIG. 5 is a schematic block diagram showing a circuit configuration of such a terrestrial digital broadcast receiver 1000 according to the first embodiment.

Referring to FIG. 5, terrestrial digital broadcast receiver 1000 receives a signal modulated according to the OFDM modulation method by antenna 100, and transmits the signal to tuner unit 1.
02 downconverts to baseband.

Further, the output of the tuner unit 102 is A / D
After performing analog-to-digital conversion in the conversion circuit 104 and performing various synchronization processes such as clock synchronization and symbol synchronization in the synchronization circuit 106, a fast Fourier transform unit (hereinafter referred to as FF) is performed.
The received signal is input to the (T unit) 108.

After the Fourier transform is performed in FFT section 108, decoding is performed by OFDM frame decoder 110, and further demodulation by differential demodulation section 112 or scattered pilot by SP demodulation section 114, and TMCC Transmission and Multiplexing Configurat (TMCC) by the decoding unit 116
ion control) signal is decoded.

Here, the TMCC signal conveys information such as the type of modulation scheme currently used and the coding rate of error correction. At the time of differential demodulation by the differential demodulation unit 112, data modulated by the DQPSK method is QPSK.
It is converted into data that can be demodulated by the method.

Next, a pilot pulse is generated in pilot pulse generating section 120, and TMCC information is analyzed in TMCC information analyzing section 122 to generate a signal necessary for subsequent processing calculations.

In parallel with these processes, the reliability detection processing unit 118 performs a process of detecting the reliability information of the FFT output data, as described later.

Subsequently, based on these signals, the frequency deinterleave processing unit 124 performs frequency deinterleave, and the modulation division unit 128 divides the signal for each modulation scheme, and the predemapping processing units 130, 1
32, 134, "Predemapping processing"
Perform

In parallel with the frequency deinterleaving process,
The demapping reference value calculation unit 126 calculates a reference value for demapping as described later. As described in detail later, the “predemapping process” is to determine which reference value the input I-axis data and Q-axis data are closest to for each carrier, This is a process of converting the data into bit data of a format having information on the direction and distance of each of I and Q of the data as viewed from the reference point.

Here, predemapping processing section 130 performs processing corresponding to the received signal in the QPSK modulation method, predemapping processing section 132 performs processing corresponding to the received signal in the 16QAM modulation method, and predemapping processing section. 134 performs processing corresponding to the received signal in the 64QAM modulation method.

Each predemapping processing unit 130, 13
The modulation and synthesis section 136 synthesizes a signal with the output from the second and 134 according to the modulation method.

A reliability correction processing unit 138 performs a correction process on the predemapping result from the modulation / combination unit 136 based on the reliability information from the reliability detection unit 118.

Subsequently, the time deinterleave processing unit 14
At 0, a time deinterleaving process is performed, and the output data is converted by a bit conversion unit 142 into a data format for performing subsequent processing.

After hierarchical division section 144 performs hierarchical division according to the hierarchy of the received signal, bit deinterleave processing sections 146.1 to 146.3 and depunctured processing sections 148.1 to 148.3 are performed for each hierarchy. Perform bit deinterleaving and depuncturing.

Depuncture processing units 148.1 to 14
The TS reproducing unit 154 reproduces a TSP of each layer synthesized by the layer synthesizing unit 150 based on the signal from 8.3 or a null TSP from the null packet generating unit 152 into a transport stream (Transport Stream: TS), The Viterbi decoding unit 156 performs error correction on the signal from the TS reproducing unit 154 by Viterbi decoding.

Finally, the output of the Viterbi decoding unit 156 is divided again by the layer division unit 158 according to the layer of the received signal, and the byte deinterleave processing unit 16
0.1 to 160.3 and energy despreading section 162.1
162.3 perform byte deinterleaving and energy despreading, perform hierarchical composition again, and perform error correction by Reed-Solomon decoding in a Reed-Solomon decoding unit (hereinafter, RS decoding unit) 164, and then perform final error correction. As a transport stream TS.

Thereafter, MPEG decoding and digital / analog conversion are performed in the same manner as in FIG.
Video / audio output is obtained.

The terrestrial digital broadcast receiver 1 described above
000, the conventional receiving apparatus 500 shown in FIG.
The main differences from the configuration of FIG. 0 are, first, the reliability detection processing unit 118 and the demapping reference value calculation unit 12
6 is provided. Second, in place of the demapping circuit 16 of the conventional receiver 5000, pre-demapping processing units 130, 132, and 134 are provided.
And a bit conversion circuit 142. Third, the time deinterleave circuit 15
Instead of the time deinterleave processing unit 140.

Hereinafter, among the components of the terrestrial digital broadcast receiver 1000 shown in FIG. 5, the reliability detection processing unit 118, the demapping reference value calculation unit 126, the predemapping processing units 130 to 132, and the reliability The gender correction processing unit 138 will be described in more detail below.

[Operation of Reliability Detection Processing Unit] First, the configuration of the reliability detection processing unit 118 will be described.

A received signal may include a carrier whose reliability is low due to the influence of multipath, interference, noise, and the like. Therefore, the reliability detection processing section 118 after FFT uses the scattered pilot signal (hereinafter, SP signal) among the pilot signals to detect the degree of reliability of each carrier from the dispersion of the SP signal.

For evaluation of the reliability of each carrier using such an SP signal, see Reference 1: Harada, Aizawa, Sato,
Sugimoto, "Error Control Considering Terrestrial Channel Characteristics", 19
It is described in the 1998 Annual Meeting of the Institute of Image Information and Television Engineers 3-1.

In the following, the method of obtaining the reliability R will be described briefly from the variance of SP as described above. That is, the reception level of the reception SP is set to I (t, f), Q (t,
The reliability R when f) is obtained from the following equation (1).

[0060]

(Equation 1)

Where A is a coefficient including a threshold, Ire
f (f) and Qref (f) are the received signals I (t, f),
This is the average value of Q (t, f) in the time direction. The numerator of the equation (1) indicates the average value of the reception level, and the reliability R increases as the reception amplitude increases. Further, the denominator of the equation (1) indicates a variance, and the reliability R decreases as the interference increases.

That is, the reliability detection processing section 118 focuses on the SP signal periodically located in the symbol,
An average value of the level of the P signal is calculated and compared with the level of each SP to detect the reliability of the SP signal. The reliability detection processing unit 118 uses the reliability R as the reliability information of the SP signal and, for a carrier other than the SP, the reliability information of the SP signal closest to the carrier as the reliability information of the carrier. In this way, the reliability information is added to all the carriers in the layer of the synchronous modulation.

However, since the SP signal is included only in the synchronous modulator, the reliability information is detected only in the synchronous modulator.

FIG. 6 is a diagram showing reliability information added by the reliability detection processing unit 118. Reliability detection processing unit 118
Outputs a detection result as a 3-bit signal that can be reflected in the weighting of the Viterbi soft decision as shown in FIG.

The reliability of the pilot signal carrier is detected similarly to the data signal carrier.

FIG. 7 is a diagram showing the distribution of SP signals in an OFDM frame. The SP signal is sent to the synchronous modulation section 12
It is configured to be inserted once into the carrier and once into every four symbols.

[Operation of Demapping Reference Value Calculation Unit 126] FIG. 8 is a diagram for explaining the operation of the demapping reference value calculation unit 126.

The demapping reference value is obtained by converting the pilot average value to a data signal level and multiplying by a coefficient for calculating a reference value determined for each modulation scheme as shown in FIG.

The pilot signal is multiplied by 4/3 as compared with the data signal on the modulation side. In order to convert the pilot average value to the level of the data signal, the pilot signal is converted to 3 /
Multiply by four. The minimum reference value of each modulation method is DQP
For S and QPSK, 1/1 of the pilot signal after level conversion
In the case of １６2, 16 QAM, it can be obtained by 1 / √10 times the pilot signal after level conversion, and in the case of 64 QAM, it can be obtained by 1 / √42 times the pilot signal after level conversion. That is, the demapping reference value is obtained by a constant multiple of the pilot average value.

However, the demapping reference value calculation unit 126
Various methods can be considered for the method of extracting and calculating the pilot average value for improving the accuracy of the demapping reference value.

FIG. 9 shows a demapping reference value calculating section 126.
FIG. 2 is a schematic block diagram showing the configuration of FIG.

Referring to FIG. 9, demapping reference value calculating section 126 includes pilot signal extracting section 200 for extracting a pilot signal from the data received from TMCC information analyzing section 122, and pilot signal extracting section 200 for extracting pilot signals. If the data is data of a hierarchical layer of synchronous modulation, in order to improve the accuracy of the demapping reference value, a pilot signal reliability determination section 202 for determining reliability of the pilot signal and extracting a reliable pilot signal. When,
When the data from pilot signal extraction section 200 is an average value calculation section 204.1 for calculating the average value of the signal from pilot signal reliability determination section 202 and the pilot signal is Average value calculation section 204.2 for calculating the average value of the signal from extraction section 200
And an output from the average value calculation units 204.1 and 204.2, and an average value selection unit 206 that selects the average value of the pilot signal for each layer. A reference value calculation unit 208 that calculates a demapping reference value corresponding to the modulation scheme of each layer.

In the following, the demapping reference value calculation unit 12
In 6, a description will be given of a configuration capable of performing an operation for extracting a reliable pilot signal and calculating a demapping reference value.

(First Method) First, when the received signal is composed only of the synchronous modulation method, the demapping reference value calculating section 126 selects, among all pilot signals included in one symbol, A pilot signal determined to be reliable is extracted, and an average value of the extracted pilot signal is obtained. It is possible to adopt a configuration in which the pre-demapping is performed by applying the demapping reference value obtained from the pilot average value to all data in the symbol.

In other words, among the pilot signals inserted at equal intervals in the layer of the synchronous modulation of the received signal, S
Based on the P signal, the reliability detector 1 as shown in FIG.
At 18, a reliability information signal as shown in FIG. 6 is generated only in the layer of synchronous modulation.

In the case of a symbol consisting only of the layer of synchronous modulation, since reliability information is added to all pilot signals, the reliability of all pilot signals is determined using this signal, and a reliable pilot signal is obtained. A process of extracting and adding only the signals to obtain a pilot average value is performed.

(Second System) Second, when the received signal is composed of a combination of the differential modulation system and the synchronous modulation system, the demapping reference value calculation unit 126 Are divided into a differential modulator, which is a set of layers modulated by the differential modulation method, and a synchronous modulator, which is a set of layers modulated by the synchronous modulation method.

Since no SP signal is inserted in the differential modulation section, no reliability information is detected for the carrier of the differential modulation section. In the second method, it is particularly assumed that the difference between the pilot signal average values of the differential modulator and the synchronous modulator is large.
In this case, it is considered that the accuracy is improved by obtaining the demapping reference value by using different pilot average values in the differential modulation section and the synchronous modulation section.

Therefore, all pilot signals included in the differential modulation section are extracted, and the average value calculation section 204.2 calculates the average value of the pilot signals in the differential modulation section.

On the other hand, with respect to the synchronous modulation section, a pilot signal determined to be reliable by pilot signal reliability determination section 202 is extracted from all pilot signals included in the synchronous modulation section, and average value calculation section 204.2. The average value of the extracted pilot signal is obtained.

The average value selecting section 206 obtains a demapping reference value obtained from the pilot average value for each modulation section, and applies the demapping reference value thus obtained to data in each modulation section. Perform predemapping.

(Third System) Third, similarly to the second system, when the received signal is composed of a combination of the differential modulation system and the synchronous modulation system, all the layers within one symbol (maximum) 3
(Hierarchy) is divided into a differential modulator, which is a set of hierarchies modulated by the differential modulation scheme, and a synchronous modulator, which is a set of hierarchies modulated by the synchronous modulation scheme.

Since no SP signal is inserted in the differential modulator, no reliability information is detected for the carrier of the differential modulator. In the third scheme, it is particularly assumed that the difference between the average value of the pilot signal of the differential modulation unit and the synchronous modulation unit is small. In the case of the third scheme, the accuracy of the differential modulation unit is higher when the demapping reference value is obtained by using the pilot average value of the synchronous modulation unit in consideration of the reliability than by the pilot average value whose reliability is unknown. It is thought to improve.

Therefore, average value selection section 206 does not employ the pilot average value of the differential modulation section, and determines that pilot signal reliability determination section 202 can be reliable among all pilot signals included in the synchronous modulation section. The extracted pilot signal is extracted, and the average value of the extracted pilot signal obtained in average value calculation section 204.1 is adopted.

Predemapping is performed by applying the demapping reference value obtained from the pilot average value to all data in the symbol.

(Fourth Scheme) Fourth, in the first scheme as described above, the number of pilot signals determined to be reliable by pilot signal reliability determination section 202 is determined by average value calculation section 204.1. Is equivalent to the divisor of the division process of the averaging process. Since the divisor takes a free value within a range not exceeding the total number of pilot signals, there is a possibility that the division circuit of the average value calculator 204.1 becomes complicated.

Thus, as a fourth method, pilot signal reliability determining section 202 determines the number of pilot signals determined to be reliable among all pilot signals included in one symbol by an appropriate number of powers of two. The extraction and average value calculation unit 204.1 is configured to calculate the average value of the extracted pilot signals. By using such a method, the division processing can be performed only by the bit shift, and the circuit scale can be reduced.

The pre-demapping is performed by applying the demapping reference value obtained from the pilot average value to all data in the symbol.

(Fifth Method) Fifthly, even in the second method as described above, when calculating the pilot average value of the synchronous modulator, the division circuit is used for the same reason as in the first method. Can be complicated.

Therefore, as a fifth method, of all pilot signals included in the synchronous modulation section, pilot signals determined to be reliable are extracted by an appropriate number of powers of 2, and the extracted pilot signals are extracted. We will find the average value. By using such a method, the division process can be performed only by the bit shift, and the circuit scale can be reduced.

As for the differential modulator, all pilot signals included are extracted as in the second method as described above, and the average value of the pilot signals in the differential modulator is obtained.

For each modulator, pre-demapping is performed by applying the demapping reference value obtained from the pilot average value to the data in the modulator.

(Sixth Scheme) Sixth, even in the third scheme as described above, when calculating the pilot average value of the synchronous modulation section, for the same reason as in the first and second schemes,
The division circuit may be complicated.

Therefore, as a sixth method, among all the pilot signals included in the synchronous modulation section, pilot signals judged to be reliable are extracted by an appropriate power of two, and the extracted pilot signals are extracted. The average value is determined. With such a configuration, the division process can be performed only for the bit shift, and the circuit scale can be reduced.

The pre-demapping is performed by applying the demapping reference value obtained from the pilot average value to all data in the symbol.

According to any one of the above methods, it is possible to improve the accuracy of the demapping reference value obtained by multiplying the pilot signal by a constant.

[Predemapping processing units 130 to 134
Operation] The predemapping processing units 130 to 134 determine, for each carrier, which reference value the input I-axis data and Q-axis data are closest to. The data is converted into bit data of a format having information on the directions and distances of each of the I and Q data.

That is, the predemapping processing unit 130-
The data 134 is Fourier-transformed by the FFT unit 108 and frequency-deinterleaved by the frequency deinterleave processing unit 124 by demapping the data from the I-axis data and the Q-axis data into data directly representing a value. This demapping is performed according to the modulation scheme on the transmission side, but in order to be able to support 64 QAM with the maximum number of bits,
The number of bits of the data after demapping is 6. When the modulation is QPSK, the upper 2 bits of the 6 bits are
In the case of QAM, the upper 4 bits of the 6 bits are used, and the other bits are redundant bits.

Here, OFDM for terrestrial digital broadcasting
In the modulation of the system, a convolutional code is adopted as an error correction code, and error correction is performed using this code in demodulation. One of the convolutional code correction methods is a Viterbi decoding method, and the receiving apparatus 1000 can perform error correction by the Viterbi decoding unit 156.

In the Viterbi decoding method, besides the method of setting the input data to "1" or "0", there is a method of using the certainty of the value of the input data. That is, the input data is represented by 3 bits, and the value of 3 bits is “11”.
When it is "1", the data values are almost certainly "1" and "10".
In the case of "1", the data value is likely to be "1", but there is a slight possibility that the data value is "0", and the error correction capability is improved by using this method.

In order to make this possible, it is also possible to adopt a configuration in which, at the time of demapping by the predemapping circuits 130 to 134, a bit indicating the certainty of the value is added to 6 bits indicating the value of the data. . Hereinafter, this method will be described.

FIG. 10, FIG. 11, and FIG.
FIG. 9 is a constellation diagram showing an arrangement of data values in PSK, 16QAM, and 64QAM modulation.

These arrangements are called gray (GRAY) codes, and the values of adjacent grid points on the IQ coordinate plane differ by only one bit.

For example, the value “000” near the upper right of FIG.
Looking at the grid point of “011”, the value of the grid point on the left side is “001011”, and the value of the grid point on the right side is “000”.
001 ", the value of the upper grid point is" 000010 ", and the value of the left grid point is" 000111 ".

The demapping is to reproduce the data arrangement of FIG. 10, FIG. 11, or FIG. 12 according to the modulation of QPSK, 16QAM and 64QAM. However,
Due to the effects of fading and the like on the transmission path, the coordinates indicated by the I-axis data and the Q-axis data after the Fourier transform deviate from the grid points. This shift is divided into the I-axis direction and the Q-axis direction, and the shift in each direction is represented by n bits, and these are added to data values as information indicating certainty. That is, demapping data is represented by (6 + 2n) bits.

The number of bits n for indicating the shift may be any number as long as it is 1 or more. However, the number of bits n is appropriately set to about 3 because it affects the memory capacity required for time deinterleaving. In that case, the predemapping circuit 1
Each data output by 30 to 134 has 12 bits. The bit conversion unit 142 converts each of the 2.4 or 6 bits indicating the value of the 12-bit data into 3 bits in a format including certainty, and is suitable for processing in the Viterbi decoding unit 156. To data in the specified format.

As a specific example, in modulation by 64QAM,
FIG. 12 shows I-axis data and Q-axis data in demapping.
The case where the position P indicated by ◎ is indicated will be described.

The position P is closest to the lattice point of the value "0000011", and this value is used as the data value. However, the certainty of the values of the lower two bits (the fifth bit and the sixth bit) is low. Therefore, the position P from the lattice point of the value “0000011”
Is 3 in each of the I-axis direction and the Q-axis direction.
Expressed in bits. Here, the most significant bit (MSB) of the three bits is a code indicating the direction (positive or negative) of the shift, and the magnitude of the shift is expressed by the lower two bits. The magnitude of the deviation is expressed in four stages from “00” to “11”.

In the case of the position P, the position is shifted in the positive direction in the I-axis direction, and its size is slightly more than １ ／ of the distance to the right grid point. In the Q-axis direction, it is shifted in the positive direction and its size is slight, so it is set to “101”. The entire data to which the information indicating the shift is added is “000001111010”.
This data is supplied to the bit conversion unit 142 without being changed by time deinterleaving.

The bit conversion section 142 assigns a bit having a high possibility that the value is “1” to “111” and a bit having a high possibility that the value is “0” out of the six bits indicating the data value to “111”. 000 ", and a bit other than either of these bits is set to any one of" 110 "to" 001 "according to the degree to which the value is more likely to be" 1 "or" 0 ". . In this case, the upper four bits indicating the data value are all likely to be the value “0”, so these are set to “000”, “000”, “000”, “000”. The fifth bit is set to “101” based on the value “1” and the information “110” of the seventh to ninth bits, and the sixth bit is set to “1” and “10” of the tenth to twelfth bits.
The information "1" is set to "110" .These 6 data consisting of 3 bits are provided to the Viterbi decoding unit 156 and used for error correction.

As described above, by adding information indicating the certainty of a value to data at the time of demapping, error correction becomes possible, and data can be reproduced well.

As described above, in such a configuration, the predemapping circuits 130 to 134 convert the input data into soft-decision Viterbi decoding predemapping data according to the modulation scheme while referring to the current TMCC information. Output.

[Operation of Reliability Correction Processing Unit 138]
The correction processing based on reliability will be described.

The reliability correction processing unit 138 determines reliability based on the reliability information of each carrier as shown in FIG. 6, and when it is determined that correction is necessary, the absolute value of the data distance information viewed from the reference point. , A value corresponding to the degree of correction is added and output.

[Operation of Time Deinterleaving Processing Unit 140] Time deinterleaving processing unit 140 time deinterleaves the data after the frequency deinterleaving and the reliability correction processing. In these deinterleaving, each data is handled as (6 + 2n) bits.

As described above, the bit conversion section 142 converts the time-deinterleaved (6 + 2n) -bit data into a Viterbi soft decision corresponding to valid 2-bit, 4-bit or 6-bit data according to the modulation method. Convert to a data format that can be processed.

In such a configuration, the data to be subjected to time deinterleaving is two data of I-axis data and Q-axis data.
Since it is one type after demapping, not type, the memory capacity required for each demapping is greatly reduced. Moreover, since each data to be demapped has a smaller number of bits than the I-axis data and the Q-axis data, the required memory capacity is further reduced.

With the above configuration, the memory capacity for the interleave processing can be reduced.

[Second Embodiment] FIG. 13 shows a second embodiment.
1 is a schematic block diagram illustrating a circuit configuration of a terrestrial digital broadcast receiver 2000 of FIG.

Unlike digital terrestrial broadcast receiver 1000, terrestrial digital broadcast receiver 2000 does not perform pre-demapping after frequency deinterleaving, but performs time deinterleaving by time deinterleaving processing section 141 first, Demapping processing units 131 and 13
3, 135 performs demapping.

Here, the demapping processing unit 131 performs QP
The demapping processing unit 133 performs a process corresponding to the received signal in the SK modulation method, and the demapping processing unit 133 performs a process corresponding to the received signal in the 16QAM modulation method.
5 performs processing corresponding to the received signal in the 64QAM modulation method.

Also, in response to not performing the predemapping process, terrestrial digital broadcast receiver 2000 is not provided with bit conversion section 142.

The operation of the demapping reference value calculation unit 126 of the terrestrial digital broadcast receiver 2000 can be the same as that of the first to sixth systems of the first embodiment.

With the above configuration, it is possible to improve the accuracy of the demapping reference value obtained by multiplying the pilot signal by a constant, as in the first embodiment.

The embodiments disclosed this time are to be considered in all respects as illustrative 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.

[0126]

As described above, the digital signal receiving apparatus according to the present invention excludes a pilot signal having low reliability by using the reliability information signal, and calculates the average value of the pilot signal. It is possible to improve the accuracy of the demapping reference value obtained by a constant multiple of.

[Brief description of the drawings]

Fig. 1 OFD received by a terrestrial digital broadcast receiver
FIG. 3 is a conceptual diagram for explaining a data structure of the M system.

FIG. 2 is a diagram showing a configuration of an OFDM symbol shown in FIG.

FIG. 3 is a diagram for explaining the structure of one OFDM segment in more detail;

FIG. 4 is a diagram for explaining the mode dependence of the configuration of one OFDM segment.

FIG. 5 is a schematic block diagram illustrating a circuit configuration of a terrestrial digital broadcast receiver 1000.

FIG. 6 is a diagram showing reliability information added by the reliability detection processing unit 118.

FIG. 7 is a diagram showing a distribution of SP signals in an OFDM frame.

FIG. 8 is a diagram for explaining the operation of the demapping reference value calculation unit 126.

FIG. 9 is a schematic block diagram illustrating a configuration of a demapping reference value calculation unit 126.

FIG. 10 is a constellation diagram showing an arrangement of data values in QPSK modulation.

FIG. 11 is a constellation diagram showing an arrangement of data values in 16QAM modulation.

FIG. 12 is a constellation diagram showing an arrangement of data values in 64QAM modulation.

FIG. 13 is a schematic block diagram illustrating a circuit configuration of a terrestrial digital broadcast receiver 2000 according to the second embodiment.

FIG. 14 is a schematic block diagram illustrating a configuration of a conventional OFDM receiving device 5000.

[Explanation of symbols]

100 antenna, 102 tuner section, 104 A /
D conversion circuit, 106 synchronization circuit, 108 FFT unit, 11
0 OFDM frame decoder, 112 differential demodulation unit,
114 SP demodulator, 116 TMCC decoder, 120
Pilot pulse generation unit, 122 TMCC information analysis unit, 118 reliability detection processing unit, 124 frequency deinterleave processing unit, 126 demapping reference value calculation unit, 128 modulation division unit, 130, 132, 134 predemapping processing unit, 131, 133, 135 Demapping processing section, 136 Modulation synthesis section, 138 Reliability correction processing section, 140, 141 Time deinterleave processing section, 142 bit conversion section, 144 Hierarchical division section, 1
46.1 to 146.3 bit deinterleave processing section, 148.1 to 148.3 depunctured processing section, 150 layer synthesis section, 152 null packet generation section, 154 TS reproduction section, 156 Viterbi decoding section, 15
8 layer division unit, 160.1 to 160.3 byte deinterleave processing unit, 162.1 to 162.3 energy despreading unit, 164 RS decoding unit, 200 pilot signal extraction unit, 202 pilot signal reliability determination unit, 20
4.1, 204.2 average value calculation unit, 206 average value selection unit, 208 reference value calculation unit, 1000, 2000 terrestrial digital broadcast receiver.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 5, 2001 (2001.7.5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0069

[Correction method] Change

[Correction contents]

The pilot signal is multiplied by 4/3 as compared with the data signal on the modulation side. In order to convert the pilot average value to the level of the data signal, the pilot signal is converted to 3 /
Multiply by four. The minimum reference value of each modulation method is DQP
For S K and QPSK, one of the pilot signals after level conversion
/ √2 times, for 16QAM, 1 / ら れ る 10 times the level-converted pilot signal, and for 64QAM, 1 / √42 times the level-converted pilot signal. That is, the demapping reference value is obtained by a constant multiple of the pilot average value.

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] FIG.

[Correction method] Change

[Correction contents]

FIG. 14

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Masayuki Yoshinaga 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. F-term (reference) 5C025 AA13 BA25 BA30 DA01 5C059 RA04 RB02 RD03 RD05 RD07 RD09 RF05 RF21 SS02 UA04 5K014 AA01 BA08 FA11 FA16 HA06 HA10 5K022 DD01 DD13 DD18 DD19 DD33

Claims (5)

[Claims] 1. A signal transmitted by an orthogonal frequency division multiplexing method in a frame unit, wherein the frame includes a plurality of symbols, and each symbol includes a guard interval and a plurality of segments that are valid data. Have
A digital signal receiving apparatus for receiving a signal transmitted with a variable data modulation scheme for each group of a plurality of segments in each of the symbols, comprising: a fast Fourier transform processing unit for performing a fast Fourier transform on a received signal; A reliability detector for detecting reliability of a pilot signal included in each segment based on an output of the fast Fourier transform processing unit; and a predetermined reliability according to a detection result of the reliability detector. Extracting a pilot signal that satisfies the following, based on an average value of the extracted pilot signal, a reference value calculating unit that calculates a reference value on a constellation corresponding to the modulation scheme, and an output of the fast Fourier transform processing unit. And at least a constellation according to a modulation scheme corresponding to each segment. Demapping processing means for outputting information indicating which reference value corresponds to the above, and decoding processing means for performing error correction by maximum likelihood decoding processing based on the output of the demapping processing means ,
Digital signal receiver. 2. The signal transmitted by the orthogonal frequency division multiplexing method has been subjected to time interleaving processing, and the digital signal receiving apparatus performs the time interleaving processing based on an output of the demapping processing means. 2. The digital signal receiving apparatus according to claim 1, further comprising: a time deinterleave processing unit that performs a time deinterleave process as an inverse transform and supplies the time deinterleave process to the decoding process unit. 3. The signal transmitted by the orthogonal frequency division multiplexing method has been subjected to time interleave processing, and the digital signal receiving apparatus performs the time interleave processing based on an output of the fast Fourier transform processing means. Performing a time deinterleaving process that is an inverse transform of, and further comprising a time deinterleaving processing unit to be provided to the demapping processing unit;
The digital signal receiving device according to claim 1. 4. The group of the plurality of segments includes: a first group having a reference signal for reliability evaluation by the reliability detection means; and a reference for reliability evaluation by the reliability detection means. A second group having no signal, wherein the reliability detecting means adds reliability information to the first group, and the reference value calculating means comprises: A first average value calculating unit for extracting a pilot signal satisfying a predetermined reliability based on the reliability information, and calculating an average value of the extracted pilot signals; The digital signal receiving device according to claim 2, further comprising: a second average value calculating unit configured to calculate an average value of the extracted pilot signals. 5. The first average value calculation means, based on the reliability information, a reliability determination means for extracting a pilot signal which satisfies a predetermined reliability by a power of 2, and an output of the reliability determination means. 5. The digital signal receiving device according to claim 4, further comprising: a dividing unit for receiving said average value.