JP2003134082A - Soft decision viterbi decoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soft decision Viterbi decoder capable of generating a suitably weighted metric value of a receiving signal having reliability when a transmission signal parameter is switched or when power level information of low reliability is continuously generated or the information is generated at high frequency by the influence of a multi-pass or the like. SOLUTION: The soft decision Viterbi decoder for weighting multi-valued metric data by using receiving power level information detected at the time of demodulating an OFDM modulation type receiving signal is provided with: a power level limitation circuit 13 for limiting the receiving power level information up to a prescribed value; and a power level increase circuit 14 for increasing the receiving power level information limited by the circuit 13 at prescribed magnification, and the receiving power level information outputted from the circuit 14 is used for weighting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to OFDM (Orthog
onal Frequency Division Multiplexing) a demodulation and decoding device for a received signal modulated by a modulation method,
The present invention relates to a decoding device that performs soft-decision decoding in Viterbi decoding when decoding an error correction code represented by a convolutional code used in OFDM modulation.

[0002]

2. Description of the Related Art In digital television broadcasting, an OFDM modulation method is used for transmitting and receiving broadcast signals. Further, in the receiver of the OFDM modulation system, the reliability is judged according to the power level at the time of receiving the signal transmitted by the OFDM modulation system, and the soft decision Viterbi decoding is carried out.

FIG. 16 shows the radio industry (ARI).
Terrestrial digital broadcasting (hereinafter referred to as “terrestrial digital television broadcasting transmission system” issued by B)
FIG. 3 is a block diagram showing a schematic configuration of a receiver for digital broadcasting).

In FIG. 16, reference numeral 1 denotes a digital modulated signal such as an OFDM modulated signal, and first reproduces a carrier signal or a clock signal from the received signal, and then uses the carrier signal or the clock signal to receive the received signal. Demodulate and convert to the original baseband signals (I, Q signals),
In addition, it is a demodulator of a digital signal that corrects the transmission path distortion of the demodulated signal. Reference numeral 2 is a deinterleaver that reproduces the original stream sequence of the demodulated signal by giving the signal demodulated by the demodulator 1 a delay time opposite to the delay time given on the transmission side. Reference numeral 3 is a Viterbi decoder that performs decoding on the original stream sequence of the demodulated signal reproduced by the deinterleaver while correcting the error in the convolved signal.
4 is a signal which is Viterbi decoded by the Viterbi decoder 3,
It is a Reed-Solomon decoder that detects a signal sequence including the parity of the Reed-Solomon code added on the transmission side, detects an error using the Reed-Solomon code, and corrects the decoded signal.

The Viterbi decoder 3 will now be described in more detail. In the Viterbi decoder, the metric value calculated from the input data I and Q values (for example, the MSB data of I and Q is extracted) is a 1-bit metric value represented by two values of "0" and "1". There are two types of hard-decision Viterbi decoders that perform Viterbi decoding using (hard-decision data), and soft-decision Viterbi decoders that perform Viterbi decoding using multi-valued metric values (for example, 3-bit metric values). From recent reports, it has become known that the soft-decision Viterbi decoder has a higher error correction capability of about 2 dB than the hard-decision Viterbi decoder. Therefore, in a conventional receiver for digital broadcasting, a soft decision circuit of a soft decision Viterbi decoder is used to calculate a multivalued soft decision metric value.

FIG. 17 is a block diagram showing a circuit configuration from the calculation of the soft decision metric to the Viterbi decoding in the conventional receiver for digital broadcasting. In FIG. 17, the same reference numerals are given to the portions having the same functions as those in FIG. 16, and the duplicate description will be omitted.

In the circuit configuration of FIG. 17, 5 is a pilot signal amplitude comparison circuit for comparing the amplitude of the pilot signal demodulated by the digital demodulator 1 with the amplitude of a known pilot signal. Reference numeral 6 is a pilot signal phase comparison circuit for comparing the phase of the pilot signal demodulated by the digital demodulator 1 with the phase of the known pilot signal. Reference numeral 7 is an I, Q signal which is a demodulated signal by the deinterleaver 2 using the amplitude comparison value obtained by the pilot signal amplitude comparison circuit 5 and the phase comparison value obtained by the pilot signal phase comparison circuit 6. 3 is a linear conversion table for generating I and Q signals, which stores linear conversion characteristic values used for reproducing the. Reference numeral 8 denotes a power level generation linear conversion table used for the deinterleaver 2 to reproduce the power level information of the demodulated signal using the amplitude comparison value obtained by the pilot signal amplitude comparison circuit 5. Reference numeral 9 is a temporary determination circuit for demapping the demodulated signals (I, Q signals) returned to the original stream sequence by the deinterleaver 2 to determine the constellation position. Reference numeral 10 denotes a metric calculation circuit that calculates a metric value from the demodulated signal returned to the original stream sequence by the deinterleaver 2 and the temporary determination data output from the temporary determination circuit 9. Reference numeral 11 is a multiplier that multiplies the metric value calculated by the metric calculation circuit 10 by the power level information of the demodulated signal reproduced by the deinterleaver 2. Reference numeral 12 is a conversion circuit that converts the metric value multiplied by the power level information indicating the reliability of the received signal by the multiplier 11 into a soft decision metric value having a predetermined number of bits.

The Viterbi decoder 3 shown in FIG.
The demodulated signal is Viterbi-decoded based on the soft-decision metric value input from 2, and the Viterbi-decoded signal is output to the Reed-Solomon decoder 4.

Next, the operation of the conventional digital broadcast receiver shown in FIG. 16 will be described. A pilot signal, which serves as a reference for signal reproduction, is periodically inserted into a received signal of digital broadcasting. The phase and amplitude of the pilot signal inserted on the transmission side are known to the pilot signal phase comparison circuit 6 and the pilot signal amplitude comparison circuit 5. Therefore, the pilot signal phase comparison circuit 6 and the pilot signal amplitude comparison circuit 5 can calculate the difference between the phase and the amplitude of the pilot signal by using the pilot signal obtained when the demodulator 1 demodulates the received signal. it can.

In the I / Q signal generation linear conversion table 7, the calculation results of both the pilot signal phase comparison circuit 6 and the pilot signal amplitude comparison circuit 5 are represented by a linear curve, and I / Q signal generation linear characteristics are represented. To generate I and Q signals (8 bits each) that are demodulated signals. In the power level generation linear conversion table 8, both calculation results of the pilot signal amplitude comparison circuit 5 are converted using the power level generation linear conversion characteristic represented by a linear curve, and the power level information (12) of the demodulated signal is converted. Bit). For example, assume that the power level information is 4095 (decimal) when the known pilot signal has an amplitude of 10. When the amplitude of the pilot signal calculated by the pilot signal amplitude comparison circuit 5 is 5, the power level generating linear conversion table 8 outputs 204 as the power level information of the demodulated signal.
7 (decimal) is output to the deinterleaver 2.

In the deinterleaver 2, the transmitting side gives the I and Q signals generated by the linear conversion table 7 for generating I and Q signals and the power level information generated by the linear conversion table 8 for generating power level. The original stream sequence is reproduced by providing a delay time opposite to that given.

In the tentative decision circuit 9, the I and Q signals reproduced by the deinterleaver 2 are demapped, and the constellation position is tentatively decided. Metric calculation circuit 10
Then, the metric value of each decoded signal is calculated from the constellation position provisionally determined by the provisional determination circuit 9 and the original stream sequence of the received signal (I, Q signal). For example,
One input signal (I, Q signal) when the modulation method is 64QAM which can maximize the transmission rate in digital broadcasting.
Since 6 pieces of data can be decoded from, the 6 pieces of metric values are output from the metric calculation circuit 10.

The multiplier 11 multiplies all the calculated six metric values by the power level information having the same time relationship (corresponding) as the metric value, so that each metric value depends on the power level information. Perform weighting.
Note that if the received power is high, the ratio of noise components to the received signal will be small, so if the signal has a high certainty (high reliability), and if the received power is low, then the reception Since the ratio of noise components and the like to the signal becomes large, it is assumed that the reliability of the signal is low (the reliability is low). Therefore, when the reliability is high, the value multiplied by the multiplier 11 becomes large,
Weighting is performed such that the difference from the metric value when there is no signal is enlarged, and when the reliability is low, the difference from the metric value when there is no signal is reduced.

On the other hand, the power level information generated by the power level generating linear conversion table 8 has a constant value in the fixed reception mode (AWGN mode) for receiving in a stationary state in which the change in electric field strength is small. However, in the case of a mode in which multipath occurs such as mobile reception (multipath mode), the received power level of the pilot signal constantly fluctuates due to the influence of the delayed carrier, so the demodulated power level information constantly fluctuates. It becomes a value. AW
The constant value in the GN mode is a value defined in advance by the system or the receiver. For example, 12
In the case of a bit, it is normalized by 255 (decimal) and defined as a level "1".

The conversion circuit 12 converts the metric value weighted by the multiplier 11 into a metric value of the number of bits that can be processed by the Viterbi decoder 3. For example, multiplier 1
When the output of 1 is a metric value that is expanded in the positive and negative areas with "0" as the intermediate value, the conversion circuit 12 offsets the input metric value, and sets a predetermined value as the intermediate value in the positive area. Convert to a metric value that takes the value of.

Further, for example, when the metric value handled by the Viterbi decoder 3 is 4 bits, the conversion circuit 12
"8" is added to the output of the multiplier 11, and a decimal value from 0 to 15 is adopted as the converted metric value.
In this case, the returned metric value of 16 or more is rounded down, and the intermediate value becomes "8".

Although depending on the configuration of the Viterbi decoder 3, when the metric value handled by the Viterbi decoder 3 is 4 bits, in the conversion circuit 12, when the input data is most likely to be "1", the metric value is "1". 0 "
Is output, "15" is output as the metric value when it is most likely to be "0", and the metric value is intermediate when the certainty of the input signal is low (when it cannot be judged as "0" or "1"). The value "8" is output.

If the conversion circuit 12 is set to an intermediate value when the reliability is low, the power level information becomes small when the reliability of the received signal becomes low due to the influence of multipath or the like. Therefore, the metric value at that time becomes small. This is to minimize the influence on the Viterbi decoded signal. In other words, the conversion circuit 12 converts the metric value "15" for "0" and the metric value "8" indicating an intermediate value of the metric value "0" for "1" and outputs the converted signal, thereby outputting the Viterbi decoded signal. Has a minimal impact on

The Viterbi decoder 3 uses the metric value "8" having low reliability, and mainly uses the metric value obtained from other input data having high reliability to obtain the maximum likelihood path. The error rate (bit error rate: BER) in decoding is increased.

In the Viterbi decoder 3, first, the difference between the metric value calculated from the received signal received in the convoluted state and the maximum likelihood path (most probable path) estimated by itself is Every time there is an input, it is calculated and integrated. Next, the Viterbi decoder 3 expands the difference between the integrated metric values (path metric values) of the maximum likelihood path and the other paths, and determines the path having the smallest path metric value each time there is an input as the maximum likelihood path. Is determined as. Then, the Viterbi decoder 3 decodes the received signal using the maximum likelihood path.

To the Viterbi decoder 3, the input metric value being an intermediate value means that an input signal having no reliability in which the decoded data is neither "1" nor "0" is input. In that case, the Viterbi decoder 3
Without using the input signal, the Viterbi decoder 3 estimates the subsequent paths only by the maximum likelihood path estimated based on the existing information.

The Viterbi decoder 3 has a low reliability when the metric value of the intermediate value is input and is less frequently compared with the input of the metric value having a high reliability, and when the metric value is inserted discontinuously. The maximum likelihood path described above can be estimated with a high metric value.

In the conventional digital broadcast receiver described above, the power level of the pilot signal does not fluctuate during normal reception in which the receiver is stationary in an environment where there is no influence of multipath or the like. A constant value is retained. Various modulation modes for the carrier of the transmission signal (64QAM, 16QAM as the modulation modes,
Since the specified value of the power level is different for each of the four modes of QPSK and DQPSK), the above constant value also differs depending on the modulation mode. Further, when the modulation mode is not switched during reception, the power level information holds a constant value, but when the modulation mode is switched, the power level information constant value is also switched.

However, when receiving in an environment affected by multipath or the like, the power level of the demodulated pilot signal also changes, and as a result, the power level information also changes. Further, as described above, when the power level information becomes small, the reliability of the received signal becomes low. In the multipath environment, since the power level information with low reliability is weighted by the multiplier 11 for all metric values, the metric value output from the conversion circuit 12 has many intermediate values.

For example, a metric value MT0 indicating "0"
And a metric value MT1 indicating “1”, and the conversion circuit 12
The metric value output from the metric value MTERR
Let xx. Then, each metric value MTERRxx when the reliability of the power level information is low in a multipath environment or the like.
Are theoretically all intermediate values around (MT0 + MT1) / 2.

When the power level information has no reliability and is completely "0", for example, in the case of a system (receiver) in which Viterbi decoding is performed with a 4-bit metric value in a 64QAM modulation mode, the conversion circuit 12 is used. From the above, for all (6) metric values to be decoded, the metric value "8" representing the intermediate value between "0" and "1" is continuously output and input to the Viterbi decoder 3.

However, in the actual reception in the multipath environment, the above-mentioned power level information is completely "0".
Unexpectedly, the power level information often takes a neighborhood value close to “0” due to noise or the like.
Even when this power level information is not “0” but a neighborhood value close to “0”, the metric value output from the conversion circuit 12 in the conventional soft decision Viterbi decoding apparatus is
Intermediate values are output continuously. As for the intermediate value, various modulation modes (64QAM, 16Q as the modulation mode)
The specified value is different for each of the four modes of AM, QPSK, and DQPSK.

[0028]

However, when the power level information is not "0" but a near value close to "0", the power level of the received signal is generally lowered, so that the noise component or the like to the received signal is reduced. Not only when the ratio becomes relatively large and the reliability becomes low, but even when the power level of the received signal is sufficient, as in the case of the multipath environment described above, the received signal that passed through the multipath becomes a noise component. As a result, the power level of the reproduced pilot signal may be reduced. In that case, even if the power level information is a near value close to “0”, the received signal may have reliability.

When the power level information with low reliability near "0" continues or has a high frequency, the metric value representing the intermediate value is generated continuously or at a high frequency. In that case, it becomes difficult for the Viterbi decoder 3 to estimate the maximum likelihood path used when decoding the metric value weighted by the multiplier 11 while performing error correction,
As a result, the BER value may be deteriorated.

Incidentally, regarding whether or not the maximum likelihood path is difficult to estimate by the Viterbi decoder 3 and the BER value deteriorates, the power level information corresponding to the received signal is "0".
It is determined by a temporal ratio having a value in the vicinity (for example, how many times occur in a unit time or how many times they occur continuously).

It is known that the environment in which the metric value of the intermediate value is continuously generated varies depending on the range of the input power level information level and the parameters of various transmission signals which are different for each modulation mode. ing. The parameters of various transmission signals are classified by various modulation modes having different carrier symbol intervals, coding rates, and the like.

That is, in the conventional soft-decision Viterbi decoding apparatus, when the transmission signal parameter such as the carrier modulation method is switched, or when the power level information of the received data varies due to the influence of multipath or the like. , The intermediate value is continuously or frequently generated as the metric information weighted by the power level information. In that case, there is a problem that the error correction capability (BER value) in the Viterbi decoder 3 may deteriorate.

The present invention has been made in order to solve the above-mentioned problems, and power level information with low reliability is continuously generated due to the switching of transmission signal parameters and the effects of multipath and the like. An object of the present invention is to provide a soft-decision Viterbi decoding device that can generate an appropriately weighted metric value for a received signal having reliability when it is generated frequently or frequently.

[0034]

In order to achieve the above-mentioned object, a soft decision Viterbi decoding apparatus according to the present invention described in claim 1 has a reception power level detected when demodulating a reception signal of an OFDM modulation system. A soft-decision Viterbi decoding device that performs weighting processing on multi-valued metric data using information, and a power level limiting circuit that limits received power level information to a predetermined value, and a power level limiting circuit that limits the received power level information. A power level increasing circuit for increasing the received power level information by a predetermined magnification is provided, and the received power level information output from the power level increasing circuit is used for weighting.

According to a second aspect of the present invention, in the soft-decision Viterbi decoding device according to the first aspect, at least one transmission method of a carrier modulation mode, a convolutional coding rate, and a reception mode is selected from a received signal. A transmission system detection circuit for detecting is provided, and based on the output of the transmission system detection circuit,
The power level limiting circuit controls a predetermined value, and the power level increasing circuit controls a predetermined magnification.

According to a third aspect of the present invention, in the soft-decision Viterbi decoding apparatus according to the first aspect, a BER detection circuit for detecting a bit error rate (BER) value from a Viterbi-decoded received signal is provided, and the BER detection circuit is provided. The power level limiting circuit controls a predetermined value and the power level increasing circuit controls a predetermined magnification based on the output of the detection circuit.

According to a fourth aspect of the present invention, in the soft-decision Viterbi decoding device according to the first aspect, at least one transmission method of a carrier modulation mode, a convolutional coding rate, and a reception mode is selected from a received signal. A transmission system detection circuit for detecting and a BER detection circuit for detecting a BER value from a Viterbi-decoded received signal are provided, and the power level limiting circuit controls a predetermined value based on the output of the transmission system detection circuit and the output of the BER detection circuit. However, the power level increasing circuit is characterized by controlling a predetermined magnification.

According to the present invention of claim 5, in the soft-decision Viterbi decoding device according to claim 4, when the detection result of the BER detection circuit is less than a predetermined value, the power level limiting circuit and the power level increasing circuit. Control based on only the output of the transmission method detection circuit, and when the detection result of the BER detection circuit is equal to or greater than a predetermined value, the power level limiting circuit and the power level increase circuit determine the output of the transmission method detection circuit and the BER. It is characterized in that control is performed based on the output of the detection circuit.

According to the present invention of claim 6, in the soft-decision Viterbi decoding device according to claim 4, power level generation for converting received power level information detected when demodulating a received signal using a non-linear conversion characteristic. The power level limiting circuit limits the received power level information converted by the power level generating non-linear conversion table to a predetermined value.

According to a seventh aspect of the present invention, in the soft-decision Viterbi decoding apparatus according to the sixth aspect, the power level generating non-linear conversion table includes a plurality of power level generating non-linear conversion tables. A plurality of table selection circuits for selecting conversion characteristics based on the output of the transmission method detection circuit and the output of the BER detection circuit are provided.

Further, the present invention of claim 8 is the soft-decision Viterbi decoding apparatus according to claim 7, further comprising storage means capable of rewriting arbitrary data, and the storage means controls the soft-decision Viterbi decoding apparatus. The controller stores a plurality of non-linear conversion tables for power level generation.

According to the present invention of claim 9, in the soft-decision Viterbi decoding device according to claim 8, the storage unit stores power limit information for limiting the received power level information to a predetermined value in addition to the conversion characteristic. , The power amplification information for increasing the reception power level information limited to a predetermined value by a predetermined scale factor, and the control device outputs the BER and the BER of the transmission system detection circuit.
It is characterized in that the non-linear conversion characteristic, the power limit information, and the power amplification information are selected based on the output of the detection circuit.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. 1 is a block diagram showing a soft-decision Viterbi decoding device according to a first embodiment of the present invention. Note that, in FIG. 1, parts having the same functions as those of the conventional soft-decision Viterbi decoding device shown in FIG.

In the soft decision Viterbi decoding apparatus of FIG.
Reference numeral 3 is a power level limiting circuit that limits the power level information (12 bits) output from the deinterleaver 2 by a predetermined value preset for each modulation method. 1
Reference numeral 4 is a power level increasing circuit for increasing the power level information by multiplying the power level information output from the power level limiting circuit 13 by a predetermined value set in advance. Other configurations are the same as those of the conventional soft-decision Viterbi decoding device shown in FIG.

Next, the operation of the soft decision Viterbi decoding apparatus of FIG. 1 will be described.

In the power level limiting circuit 13, the power level information (12 bits) input from the deinterleaver 2 is set to "0" by experimental data or simulation calculation.
The range from 00 "to" FFF "(hexadecimal number, 12 Bit) is limited to a predetermined value or less. For example, when the power level limiting circuit 13 sets the predetermined value to" 0FF ", the power level limiting circuit 13 Output is less than or equal to “0FF”, and power level information larger than “0FF” such as “3FF” is limited to “0FF” and output. It may be set from a CPU (not shown) that is a control unit that controls the soft-decision Viterbi decoding device via a register (not shown) that is a unit that stores instructions and set values.

The power level increasing circuit 14 multiplies the power level information input from the power level limiting circuit 13 by limiting it to a predetermined value or less by a predetermined value preset by experimental data, simulation calculation, etc. Increase information. For example, if the predetermined value is 2 in the power level increasing circuit 14, the power level information will be doubled. Here, the power level information input to the power level increasing circuit 14 is “00F” (16
A decimal number, 12 Bit), the power level increasing circuit 14
Output is "01E", which is in a format that is left-shifted by 1 bit. When the output value of the power level increase circuit 14 overflows by multiplying by a predetermined value and becomes larger than 12 bits (“FFF”), “FFF” which is the maximum value of 12 bits is output. To do. The predetermined value used for multiplication in the power level increasing circuit 14 can be set to any numerical value within the range set by experimental data, simulation calculation, etc., for example, H /
To simplify the calculation of W etc., × 1, 2, 4,
.., etc. may be preset as predetermined values.
Further, as to which predetermined value (magnification) to be selected from the plurality of set predetermined values, as in the case of the power level limiting circuit 13 described above, for example, the control means for controlling the soft-decision Viterbi decoding device. It may be selected from a certain CPU (not shown) via a register (not shown) which is a means for storing instructions and set values.

The power level information processed by the power level increasing circuit 14 as described above is input to the multiplier 11. In the multiplier 11, as described in the description of the conventional soft-decision Viterbi decoding device shown in FIG. 17, the input metric value is weighted by the power level information. Then, in the conversion circuit 12, for example, in the case of 4-bit output, 0 to 1
A metric value weighted to have a value in the range of 5 (intermediate value: 8) is output. And the Viterbi decoder 3
Then, error correction processing and decoding are performed based on the weighted metric value.

Here, the error correction processing and decoding performed based on the metric value weighted by the Viterbi decoder 3 will be briefly described.

FIG. 2 is a part of the constellation map in the case where the modulation method is 64QAM, and is a diagram showing a specific example of the error correction processing and decoding based on the weighted metric value implemented in the Viterbi decoder 3. .

In the map of FIG. 2, the input data I,
The Q symbol is indicated by a square mark in the figure. The constellation symbol point closest to the input data is provisionally determined from this map and is indicated by a triangle mark in the figure. The six decoded signals (b0, b1, b2,
b3, b4, b5) becomes (0, 0, 1, 1, 1, 1). Using this temporary judgment value and the input signal, for example, as shown in FIG.
The metric calculation circuit 10 can calculate the metric value according to the following procedure.

For each decoded signal, W0: metric value for "0" and W1: metric value for "1". In addition, the metric value (LLX, LLY, L0 to L
5) are all squared values of the distance.

For example, the temporary decision points (0, 0, 1, 1,
For 1 and 1), the signal point with the 0th bit replaced is
(1, 0, 1, 1, 1, 1, 1). At the 0th bit of the temporary judgment point, the bit temporary judgment value on the X axis is “0”, so W0
= LLX, W1 = L0, and the multivalued metric value of b0 is (LLX-L0). Similarly, the multi-valued metric value of b2 is (L2-LLX), and the multi-valued metric value of b4 is (L4-LLX).

Further, the temporary judgment points (0, 0, 1, 1, 1,
In contrast to 1), the signal point with the 5th bit replaced is
(0, 0, 1, 1, 1, 0). At the fifth bit of the temporary judgment point, the bit temporary judgment value on the Y-axis is “1”, so W0
= L5, W1 = LLY, and the multi-valued metric value of b5 is (L5-LLY). Similarly, the multi-valued metric value of b1 is (LLY-L1), and the multi-valued metric value of b3 is (L3-LLY).

Thus, the metric value of each decoded signal is
By taking the difference between the squared value of the distance from the data “0” and the squared value of the distance from the data “1”, each data provisionally determined from the input data and decoded is
A numerical value indicates which data is closer to “1” or “0”. For example, when the metric value of an arbitrary decoded signal has a negative extreme value, it corresponds to data “1”, and when it has a positive extreme value, it corresponds to data “0”. If the metric value is "0", it means that the temporarily determined data is an intermediate value that is neither "0" nor "1".

The operations of the power level limiting circuit 13 and the power level increasing circuit 14 are as described above. However, the influence on the power level information input to the power level limiting circuit 13 and the power level increasing circuit 14 will be described below. The influence of the output value on the metric value weighted by the multiplier 11 will be described.

FIG. 3 is a diagram showing how the power level information input from the deinterleaver 3 to the power level limiting circuit 13 changes.

FIG. 3 assumes reception in an environment where multipath occurs, not in the case of fixed reception in which the change in electric field strength during reception is small. In the case of fixed reception, there is no interfering signal (noise), and since it is standardized by the transmitted pilot symbols, the output power level information P is a constant value of "1" (in this case, "0F").
F ": 255 is specified by normalizing it to a power level of" 1 "). However, in the case of multipath, the frequency characteristics of the transmission line are disturbed by the amplitude and delay time of the delayed wave, and as shown in FIG. As shown, the power level information fluctuates to various values on the time axis.
Surprisingly, when the value of "0" is taken completely due to the influence of noise, the power level information may take a value close to "0" as shown in (A) or (E) in the figure. .

FIG. 4 shows the power level information of FIG.
In the power level limiting circuit 13, “0FF” (hexadecimal number: 10
FIG. 9 is a diagram showing output power level information when power limiting processing is performed with a value of 255) in a decimal number and the power level increasing circuit 14 doubles the power level information.

First, the power level information of neighborhood values near "0" shown in (A) and (E) in FIG. 3 is doubled as shown in (B) and (F) in FIG. Of the power level information. In the regions shown in (A) and (E) of FIG. 3 and the regions shown in (B) and (F) of FIG. 4, since the power level is only doubled, the time ( It is shown in the same place on the t) axis. Further, in the place where the power level is "0" in FIG. 3, the power level does not change when the magnification is changed in FIG.

However, in the areas (B) and (F) of FIG.
Since the power level is doubled, the rate of change of the power level over time can be increased. That is, by increasing the power level information by a predetermined scale factor, the curve of the power level information has a sharply larger power value level. In addition, (F) of FIG.
In the area, the power value level exceeds the normalization level due to the doubling.

As for the effect of this on the metric value after weighting, the intermediate value is the same as before in the place where the power level is "0", and in the area (B) of FIG. Since the intermediate value decreases in the region where the power level information is small, it is possible to reduce the continuity of the intermediate level information. That is, in the present embodiment, the input power level can be clearly selected as the metric value of "0" or "1". This means that the Viterbi decoder 3 in the subsequent stage can more easily determine the maximum likelihood path, and as a result, the BER value can be improved depending on the receiving environment.

In the area (D) of FIG. 4, the area (C) of FIG. 3 in which each power level information is large is doubled. Further, in the power level limiting circuit 13 of FIG. 1, “0FF” (1
The output power level information when the power limiting process is performed with a value of 255) in the 0-ary is shown. The area in FIG. 4D is converted into a constant value of "1FE" as shown.

From the above, in addition to the region (B) of FIG. 4 described above, the intermediate value decreases in the region where the power level information is large, so that it is easier than in the conventional case to use "0" or "1" It can be seen that the metric values can be sorted.

From the above, in the present embodiment, the power level limiting circuit 13 is provided in advance to appropriately limit the power level information input at a predetermined value or more, and the amplification operation in the power level increasing circuit 14 at the subsequent stage is performed. It is understood that the BER value (reception performance) after Viterbi decoding can be improved by appropriately controlling according to various transmission signal parameters and reception environment. It should be noted that the above description that power level information is appropriately limited and amplification operation is appropriately controlled means that limiting power level information with a significantly small value and controlling amplification operation with a significantly large value may result. This is because the reception performance (BER value) may be deteriorated.

Various environments are assumed as the receiving environment at the time of receiving the digital broadcast, and not only fixed reception but also mobile reception are assumed. In particular, in the case of mobile reception, due to the interference of the delayed carrier, for example, (1) when the period fluctuation of the demodulated received signal is large and the amplitude fluctuation is large, (2) conversely, the period fluctuation is long, and Various cases such as small amplitude fluctuations are assumed.

In the present embodiment, in the former case (1), for example, the power level information input to the power level limiting circuit 13 is not restricted, and the power level increasing circuit 14 is configured to operate in the present embodiment. By controlling so as not to increase the magnification, it is possible to reduce the continuous intermediate values of the metric values. And
Since the intermediate values of the metric values are not continuous, the Viterbi decoder 3 can easily select the maximum likelihood path, and the BER value (reception performance) can be improved. Further, in the present embodiment, when the latter (2) period fluctuations are long and the amplitude fluctuations are small, for example, the power level information inputted in the power level limiting circuit 13 is limited to increase the power level increasing circuit. By controlling to amplify at a predetermined magnification in 14, it is possible to reduce the continuation of the intermediate value of the metric value, and as a result, it is possible to improve the BER value (reception performance).

Embodiment 2. In the first embodiment described above, the power level limiting circuit 13 and the power level increasing circuit 14
The error rate (BER value) after Viterbi decoding was able to be improved by providing and controlling both. But,
For example, when a transmission signal parameter in a system such as a carrier modulation system is changed, it is necessary to change the control value of each processing circuit described in the first embodiment. Therefore, even when the transmission signal parameter or the like changes, the power level limiting circuit 13 and the power level increasing circuit 14
A configuration capable of appropriately changing each control value of is shown below as a second embodiment.

FIG. 5 is a block diagram showing a soft decision Viterbi decoding apparatus according to the second embodiment of the present invention. Second Embodiment
Then, in addition to the first embodiment shown in FIG. 1, a transmission system detection circuit 15 for detecting a transmission signal parameter such as a carrier demodulation system from the received signal is provided. Other configurations are similar to those of the first embodiment.

Next, the operation will be described. In the following description, description of the same operations as those in the first embodiment will be omitted, and only the operations added to the first embodiment will be described.

As shown also in the first embodiment, in order to improve the BER value output from the Viterbi decoder 3, the power limit value of the power level limiting circuit 13 and the magnification value of the power level increasing circuit 14 are set as follows. It is necessary to set a different predetermined value for each transmission signal parameter of the received signal. The various transmission signal parameters are, for example, carrier modulation mode (16QAM, 64QAM, QPSK, etc.), convolutional coding rate (1/2, 2/3, 3/4, 5/6, 7).
/ 8) and the reception mode (Mode 1, 2, 3).

In the present embodiment, first, for each combination of the various transmission signal parameters, the control value (power level limit value) of each processing circuit (power level limit circuit 13, power level increase circuit 14) that can improve the BER value is obtained. And power ratio)
Is determined in advance by a reception performance detection experiment using the system, a simulation, or the like.

The transmission system detection circuit 15 has a function of detecting information necessary for a transmission signal such as a carrier demodulation system, a convolutional coding rate and a transmission mode from the received signal. The information necessary for the transmission signal is, for example, TMCC (Transmis), which is shown in the OFDM modulation method specified by ARIB.
sion and Multiplexing Configuration Control)
It is a control signal. Transmission method detection circuit 15 in the receiver adopting the OFDM modulation method specified by ARIB
Then, the TMCC information is detected as information (various transmission parameter information) necessary for the above-mentioned transmission signal.

The transmission system detection circuit 15 that has detected various transmission signal parameters detects, for each of the detected transmission signal parameters,
An optimum control value for improving the BER value is selected from the control values determined in advance for the power level limiting circuit 13 and the power level increasing circuit 14 and set to each.

In the present embodiment, the configuration as described above is adopted,
Even if the transmission signal parameter in the system is changed by the operation, the power level limiting circuit 1
3 and the respective control values of the power level increasing circuit 14 can be appropriately changed, so that the continuous intermediate value of the metric values can be reduced, and as a result, the BER value (reception performance) can be improved. .

Third Embodiment In the first embodiment described above, the power level limiting circuit 13 and the power level increasing circuit 14
The error rate (BER value) after Viterbi decoding was able to be improved by providing and controlling both. However, the control value in the first embodiment is set in advance by experiments, simulations, etc., and it is not always possible to maintain good reception performance even if the reception environment changes. Therefore, by measuring the BER value after Viterbi decoding so as to be able to adaptively respond to changes in the actual reception environment, and feeding back the result to each control value of the power level limiting circuit 13 and the power level increasing circuit 14. A configuration capable of maintaining good reception performance even if the reception environment changes is shown below as a third embodiment.

FIG. 6 is a block diagram showing a soft decision Viterbi decoding apparatus according to the third embodiment of the present invention. Third Embodiment
Then, in addition to the first embodiment shown in FIG. 1, a BER detection circuit 16 for detecting the BER value from the Viterbi-decoded output of the Viterbi decoder 3 is provided. Other configurations are similar to those of the first embodiment.

Next, the operation will be described. In the following description, description of the same operations as those in the first embodiment will be omitted, and only the operations added to the first embodiment will be described.

The BER detection circuit 16 includes the Viterbi decoder 3
Output signal is input, and convolution processing is performed again on the data decoded by the Viterbi decoder 3 using the maximum likelihood path obtained for decoding. And the data and B
The BER value in the data after Viterbi decoding is calculated by comparing the number of corrected data with the data input to the ER detection circuit 16. Furthermore, BER
The control values of the power level limiting circuit 13 and the power level increasing circuit 14 are determined by constantly monitoring the BER value obtained by the detection circuit 16 with a CPU (not shown) or the like so as to obtain a better BER value. To do.

For example, in the environment where a multipath occurs due to mobile reception or the like, and the pilot signal fluctuates greatly due to the influence of the delayed carrier, a case where good reception performance is not obtained in the receiver will be described. In that case, BE
The R value may be worse than the intended value or a predetermined value. In that case, in the present embodiment, the BER value can be improved by changing the control values set in the power level limiting circuit 13 and the power level increasing circuit 14 as described above.

The operation in the present embodiment may be, for example, a changing operation in which the setting value of the power level limiting circuit 13 is decreased and the setting magnification of the power level increasing circuit 14 is increased, and vice versa. There is also a possibility of doing the action.

As described above, in the present embodiment, the output of the BER detection circuit 16 is monitored by using the control means such as the CPU,
The power level limiting circuit 13 and the power level increasing circuit 1 so that the BER value becomes the smallest (the error becomes the smallest).
Feedback control of each set value of 4 is appropriately performed. With this control, in the present embodiment, even in an environment where the reception environment changes, it is possible to adaptively respond to the change in the reception environment, so that good reception performance can be maintained. It should be noted that many methods are known as feedback control methods, and in the present embodiment, any method among them can be used.

Fourth Embodiment In the second embodiment described above, the power level limiting circuit 13 and the power level increasing circuit 14
Each control value of is configured so that an appropriate value can be set for each change of the transmission signal parameter.

Further, in the above-described second embodiment, the power level limiting circuit 13 and the power level increasing circuit 1 are provided under the environment in which the transmission signal parameters of the system are switched variously.
The control value of 4 is set to the optimum control value obtained in advance for each detected transmission condition of the system to improve the error rate <BER value> after Viterbi decoding. However, in an actual reception environment, for example, even when a multipath such as mobile reception occurs even in a reception environment where the transmission signal parameters of the system are constant conditions (Mode 1, 64QAM, coding rate: 3/4, etc.) , The pilot signal always fluctuates due to the influence of the delayed carrier wave. Therefore, the power level information demodulated by the demodulator 1 always has a value that fluctuates, and good reception performance may not be obtained even if the control value obtained in advance by experiments or the like is used. In other words, the control values obtained in advance for the power level limiting circuit 13 and the power level increasing circuit 14 may not be applicable to all reception environments during actual use.

Further, in the third embodiment, the BER value after Viterbi decoding is monitored, and the result is monitored by the power level limiting circuit 13.
By reflecting each control value of the power level increasing circuit 14 and adaptively responding to the actual change of the receiving environment, it is possible to maintain good receiving performance even if the receiving environment changes.

Therefore, combining the second and third embodiments,
The BER value after Viterbi decoding is monitored, and the result is used to
It is considered that both the transmission signal parameters of the system and changes in the reception environment can be dealt with by modifying the optimum control values obtained in advance for the power level limiting circuit 13 and the power level increasing circuit 14. However, when the functions of both the above-described embodiments are combined, the control values for the power level limiting circuit 13 and the power level increasing circuit 14 cannot be simply combined. Therefore, in the fourth embodiment described below, since the above-described both embodiments are combined, each control value described above is switched by both the change of the transmission signal parameter of the system and the BER value, and the BER after Viterbi decoding is performed. A case of improving the value will be described.

FIG. 7 is a block diagram showing a soft decision Viterbi decoding apparatus according to the fourth embodiment of the present invention. Fourth Embodiment
Now, a case is shown in which the BER detection circuit 16 of the third embodiment is added to the second embodiment shown in FIG. The individual configurations are the same as those of the second embodiment or the third embodiment.
Similar to that shown in.

Next, the operation will be described. In the following description, the description of the same operation as in the second or third embodiment is omitted, and the second or third embodiment is omitted.
Only the operation added to is described.

In the present embodiment, the transmission system detection circuit 15
The power level limiting circuit 13 controls a predetermined value, and the power level increasing circuit 14 controls a predetermined magnification based on the output of the power supply signal BER and the output of the BER detection circuit 16.

More specifically, when the detection result of the BER detection circuit 16 is less than the predetermined value, the power level limiting circuit 13 and the power level increasing circuit 14 are controlled based on only the output of the transmission method detection circuit 15. When the detection result of the BER detection circuit 16 is equal to or more than a predetermined value, the power level limiting circuit 13 and the power level increasing circuit 14 are controlled based on the output of the transmission method detection circuit 15 and the output of the BER detection circuit 16. I do.

That is, basically, while the operation of the second embodiment is being performed, the BER detection circuit 16 of the third embodiment monitors. Therefore, each transmission signal parameter detected by the output transmission system detection circuit 15 is detected. The optimum control value corresponding to the power level limiting circuit 13 and the power level increasing circuit 14
The operation up to each setting is the same as that of the second embodiment. However, in this embodiment, the BER
Depending on the result of the detection circuit 16, the control values set in the power level limiting circuit 13 and the power level increasing circuit 14 are changed.

For example, in an environment in which a multipath such as mobile reception occurs and the pilot signal fluctuates greatly due to the influence of the delayed carrier wave, the control value previously obtained by the measurement experiment or the like as in the second embodiment. When set to, good reception performance cannot be obtained, and the BER value becomes worse than the intended BER value. Then, the BER detection circuit 16 detects the deterioration of the BER value from the output of the Viterbi decoder 3. In that case, the BER detection circuit 16 changes the control values set in the power level limiting circuit 13 and the power level increasing circuit 14 so as to improve the BER value.

The operation in the present embodiment may be, for example, a changing operation in which the setting value of the power level limiting circuit 13 is decreased and the setting magnification of the power level increasing circuit 14 is increased, and vice versa. Although there is a possibility of the operation to be performed, the CPU or the like controls the set value that minimizes the BER value (there are few errors) while monitoring the output of the BER detection circuit 16.

Specifically, a method in which the BER detection circuit 16 is provided with a register capable of reading the detected BER value from the CPU and the CPU monitors it is considered. As described above, in the present embodiment, by performing the operation of switching both the transmission signal parameter of the system and the reception environment, the BER value after Viterbi decoding can be improved even in an environment where the reception environment changes, and good reception performance can be obtained. Can be maintained.

Embodiment 5. Embodiments 1 to 4 described above
Then, the pilot signal phase comparison circuit 6 and the pilot signal amplitude comparison circuit 5 calculate the phase difference and the amplitude difference between the pilot signal obtained by demodulating the received signal by the demodulator 1 and the reference pilot signal. ing. Then, in the I / Q signal generating linear conversion table 7, the calculated phase difference and amplitude difference are collated with the I / Q signal generating linear conversion characteristic represented by a linear curve to obtain a demodulated signal. Generates I and Q signals (8 bits each). In the power level generation linear conversion table 8, the calculated difference in amplitude is collated with the power level generation linear conversion characteristic represented by a linear curve to generate power level information (12 bits) of the demodulated signal. To do.

Therefore, in the power level generating linear conversion table 8 of the first to fourth embodiments, the linear characteristic represented by a linear curve is used as the power level generating linear conversion characteristic. .

FIG. 9 is a diagram showing an example of characteristics used in the power level generation linear conversion table 8 of the first to fourth embodiments. Further, in FIG. 9, the input data and the output power level information linearly correspond to each other at a ratio of 1: 1.

In the power level generation linear conversion table 8 of the first to fourth embodiments, when the pilot signal amplitude comparison result is input, the power level information is generated by referring to the linear curve shown in FIG. For example, when the input data of the power level generation linear conversion table 8 is P, the output power level information is Pout = P. Further, the power level information output from the power level generating linear conversion table 8 is "0" only when the input data is "0".

Further, in the multiplier 11 of the first to fourth embodiments,
As shown in FIG. 4, the characteristic of the power level information (after conversion in the present invention) used for weighting the metric value rises sharply as the value of the power level information P approaches “0”. .

This characteristic is significant in order to effectively use the value of the power level information P close to "0FF": 255 level (normalized level) in FIG. There is a possibility that it will be recognized as a conversion level.

That is, in the first to fourth embodiments described above,
If the power level of the demodulated pilot signal is lower than the normalization level, that is, even if it is determined that the reliability of the metric value is low, it has reliability when the power level is close to the normalization level. There was a possibility that it was intended to be used. However, for that reason, even when the power level of the demodulated pilot signal is extremely smaller than the normalization level and is close to “0”, that is, even when it is determined that there is almost no reliability of the metric value, There was a possibility that power levels could be mistakenly considered to be reliable.

Therefore, in the following fifth embodiment, when the power level of the pilot signal is close to the normalization level, it is effectively utilized as the weighting information as described in each of the above-mentioned embodiments, and the pilot signal A configuration will be described in which when the power level is far from the normalization level and extremely small and is close to “0”, it cannot be used as weighting information.

As a concrete method of the present embodiment, the power level information is changed to "0" by changing the linear (first-order curve) characteristic of the first to fourth embodiments shown in FIG. 9 to non-linear. Is to bias.

FIG. 8 is a block diagram showing a soft decision Viterbi decoding apparatus according to the fifth embodiment of the present invention. Embodiment 5
Then, the power level generating linear conversion table 8 in the configuration of the fourth embodiment shown in FIG. 7 is changed to a power level generating nonlinear conversion table 17 for generating the power level information of the pilot signal based on the nonlinear characteristic. ing. Other configurations are similar to those shown in the fourth embodiment.

Next, the operation will be described. In the following description, description of the same operation as that of the fourth embodiment will be omitted, and only the operation added to the fourth embodiment will be described.

In the present embodiment, the power level generating non-linear conversion table 17 refers to the non-linear conversion characteristic table for the data of the amplitude comparison result (amplitude difference) of the input pilot signals, and the power level Information is generated.

FIG. 10 is a diagram showing an example of non-linear characteristics used in the power level generating non-linear conversion table 17.

Non-linear conversion table 17 for power level generation
Then, when the non-linear characteristic of FIG. 10 is referred to, for example, when the value of the input data is P that is relatively large, the value of the power level information is almost the same as in the first to fourth embodiments. Therefore, it becomes Pout. However, in the case of Ps where the amplitude value of the input data is very small, such as when the power of the demodulated pilot signal is small, the power level information has a non-linear characteristic of almost "0". This nonlinear characteristic is
In other words, the amplitude value of the input data for which the reliability for weighting the metric value is extremely low is Ps.
In the case of, the characteristic is that the power level information is almost "0".

Power level generation non-linear conversion table 17
When the non-linear characteristic of FIG. 10 is referred to, the characteristic of the power level information after conversion with respect to the time axis of the first embodiment shown in FIG. 4 has a gradual rise only at a level close to “0”.

FIG. 11 is a diagram showing characteristics of the converted power level information with respect to the time axis in the present embodiment.

In the case of the present embodiment shown in FIG. 11, in the power level limiting circuit 13 of FIG. 8 as in the first embodiment, the power level information input with the value of “0FF” is limited, Further, the power level increasing circuit 14 doubles the power level information. However, since the non-linear characteristic of FIG. 10 is used for the non-linear conversion table 17 for power level generation, as shown in the enlarged view of point (G) of FIG. , The rising is slow. In the enlarged view of point (G) in FIG. 11, the broken line is the curve of the power level information in the case of the first embodiment, and the solid line is the curve of the power level information in the present embodiment. Further, the gradual rise is common not only at the point (G) in FIG. 11 but also in all cases where the power level information in FIG. 11 rises near “0”.

In this way, when the power of the demodulated pilot signal is very small, that is, when the reliability of the demodulated metric value is extremely low, for example, refer to the nonlinear characteristic shown in FIG. The power level information can be biased to "0" by generating the power level information. Biasing the power level information to "0" means that the multiplier 11 weights the distance square data calculated by the tentative determination circuit 9 and the metric calculation circuit 10 no matter what the large value. This means that the metric value converted by the conversion circuit 12 after being performed becomes close to the intermediate value.
For example, when the metric value for "0" is set to "15" and the metric value for "1" is set to "0" in the conversion circuit 12 as described above, the metric value "8" indicating the intermediate value or its The neighborhood value is output from the conversion circuit 12.

As described above, in this embodiment, since the table having the nonlinear conversion characteristic is used to generate the power level information, when the power of the demodulated pilot signal is very small, that is, the demodulated signal When the reliability is low, the generated power level information can be biased to “0” as compared to the power level information using the linear conversion table using the linear curve, and as a result, the metric of the demodulated signal with low reliability can be biased. Since the value can be an intermediate value between “0” and “1”, it is possible to improve the adverse effect on Viterbi decoding due to decoding of a demodulated signal having low reliability. Further, similarly to each of the above-described embodiments, the demodulated signal having the reliability even if it is less than the normalization level can be effectively used, and thus the error correction capability of the Viterbi decoder can be improved. Further, the non-linear conversion characteristic of the present embodiment can be used in combination with various controls of the fourth embodiment, so that the reception performance such as BER in Viterbi decoding can be further improved. For example, in the present embodiment, even in an environment in which both the transmission signal parameter of the system and the reception environment change,
It is possible to improve the reception performance after Viterbi decoding.

Sixth Embodiment In the fifth embodiment, the power level information is generated using a table having one type of non-linear characteristic. However, since the regulations for digital broadcasting presuppose both mobile reception and fixed reception, the reception status cannot be decided unconditionally, and broadcast may be received in various environments. To be For example, there may be a case where the received signal demodulated due to the interference of the delayed carrier has a short period variation and a large amplitude variation, and a case where the period variation is long and the amplitude variation is large.

As a case where effective reception is possible using the characteristic example of FIG. 10 shown in the fifth embodiment, for example,
It is conceivable that the demodulated received signal has a short period variation and a large amplitude variation. At this time, since the intermediate value of the metric values weighted by the power level information is unlikely to appear consecutively, the Viterbi decoder can decode the maximum likelihood path only with the metric values other than the intermediate value.

However, for example, when the period variation of the demodulated received signal is long and the amplitude variation is large due to the interference of the delayed carrier, the characteristic example of the fifth embodiment is shown in FIG.
Using the non-linear characteristic of 0 to calculate the metric value gives
It is conceivable that the period in which the input data amplitude is small continues for a long period of fluctuation. In that case, the converted power level information continues to output "0" for a long period regardless of whether the demodulated signal is normal or abnormal. Then, as the metric value converted by the conversion circuit 12 after being weighted by the power level information, the intermediate value is continuously output.

In the Viterbi decoder 3, when the intermediate value is continuously input to a certain extent or more, the maximum likelihood path is set because there is no data to be judged, although it depends on the specifications of the convolutional decoder sent from the transmitting side. The chance of making a mistake increases.

Therefore, under the receiving environment as described above,
The error correction capability of the Viterbi decoder may not be improved simply by performing conversion using only one type of characteristic in the conversion table for power level generation.

Therefore, in the following sixth embodiment, a plurality of types of tables having different nonlinear conversion characteristics are provided in advance, and a plurality of types of tables are selected according to the reception environment and the like and used for weighting the soft decision. The configuration is shown below.

FIG. 12 is a block diagram showing a soft decision Viterbi decoding apparatus according to the sixth embodiment of the present invention. In the sixth embodiment, the power level generating non-linear conversion table 17 in the configuration of the fifth embodiment shown in FIG. 8 is changed so that the power level information of the pilot signal is obtained based on the characteristics selected from the plurality of characteristics. A non-linear conversion table 18 for generating power levels to be generated, and further, a multiple table selection circuit 1 for selecting one table from a plurality of conversion tables
9 is equipped. Other configurations are similar to those shown in the fifth embodiment.

Non-linear conversion table 18 for power level generation
As the conversion characteristics stored in, not only the nonlinear characteristics of the fifth embodiment shown in FIG. 10 but also the linear characteristics of the first to fourth embodiments shown in FIG. 9 are stored.

Next, the operation will be described. In the following description, description of operations similar to those of the fifth embodiment will be omitted, and only operations added to the fifth embodiment will be described.

In this embodiment, various controls performed in the fourth embodiment are carried out. Therefore, in the receiver of the present embodiment, the transmission method detection circuit 15 detects the transmission method such as the transmission signal parameter of the system, and the BER detection circuit 16 detects the BER value, and both the transmission signal and the reception environment are detected. It can be used in a variety of environments that switch.

In the present embodiment, in addition to the above control,
Using the plural-table selection circuit 19, the control for selecting the optimum characteristic from the power level generating nonlinear plural conversion table 18 is simultaneously performed.

The selection of the characteristics in this case is similar to the fourth embodiment, that is, the transmission system detection circuit 15 and the BER detection circuit 16 are selected.
Refer to the output result of to implement. However, the optimum nonlinear characteristics that differ depending on the transmission signal parameters of the system and the reception environment are investigated in advance by measurement experiments and the like and stored as a conversion table.

In the present embodiment, for example, when the cycle fluctuation of the demodulated received signal is long and the amplitude fluctuation is large, the plural-table selection circuit 19 causes the characteristic example of the fifth embodiment. The metric value is calculated by selecting the characteristic of FIG. 9 of the first to fourth embodiments rather than the nonlinear characteristic of 10. For example, in the present embodiment, when the intermediate values of the metric values are likely to appear consecutively, the linear conversion table is selected instead of the non-linear conversion table. It reduces the number of errors in Viterbi decoding due to the intermediate value of consecutive metric values.

As described above, in the present embodiment, the control for selecting the optimum conversion characteristic from the power level generating non-linear plural conversion table 18 having plural conversion characteristics by the plural table selection circuit 19 and the row in the fourth embodiment. Since the various controls described above can be performed at the same time, the error correction capability of the Viterbi decoder can be further improved as compared with the above-described embodiments.

Seventh Embodiment In the sixth embodiment, a conversion characteristic table having a plurality of different but fixed characteristics is stored, the conversion characteristic is selected according to the reception environment, and power level information is generated according to the selected conversion characteristic. Although the metric value is weighted, it may not be possible to deal with the conversion characteristic table of fixed characteristics due to various environmental changes.

Therefore, in the seventh embodiment described below, the conversion characteristic table is configured by a general-purpose memory such as a RAM (Random Access Memory) so that the memory content can be changed from the outside such as a CPU, and the conversion characteristic can be freely changed. The following shows a case where it is configured so that can be changed.

FIG. 13 is a block diagram showing a soft decision Viterbi decoding apparatus according to the seventh embodiment of the present invention. In the seventh embodiment, the power level generating non-linear conversion table 17 in the configuration of the fifth embodiment shown in FIG.
It is the first non-linear conversion table RAM 20 which is a storage means that can be freely rewritten by control means such as U. Other configurations are similar to those shown in the fifth embodiment.

Next, the operation will be described. In the following description, description of operations similar to those of the fifth embodiment will be omitted, and only operations added to the fifth embodiment will be described.

In the present embodiment, as described above, the power level generating plural nonlinear conversion table 18 for replacing the output result of the pilot signal amplitude comparison circuit 5 of the fifth embodiment with the power level information is the first in the structure. The non-linear conversion table RAM 20 is replaced by the first non-linear conversion table RAM 20.
In the same manner as in the sixth embodiment, the optimum conversion characteristic selected from the plurality of conversion characteristics is written at the timing before the power level information is generated by the control means such as the CPU. Other operations are similar to those of the sixth embodiment.

RAM 20 for the first nonlinear conversion table
The conversion characteristic stored in the (memory) can be stored as data in the memory, written by an external CPU or the like, and can be changed to any characteristic at any timing.

That is, in the present embodiment, the sixth embodiment will be described.
In, the operation of switching the plural table selection circuit 19 is performed at the same timing as the writing operation to the first non-linear conversion table RAM 20.

Therefore, in the present embodiment, the sixth embodiment will be described.
With the configuration that supports multiple fixed tables in which power conversion characteristics are written, the conversion characteristics can be freely read / read.
Since the RAM is changed to a writable general-purpose memory, it is possible to flexibly use the power level information having the conversion characteristic optimal for the receiving environment at any timing to weight the metric value. As a result, the metric value used for Viterbi decoding is optimally weighted by the power level information that is controlled more finely according to the reception environment, so that the error correction capability of the Viterbi decoder can be further improved.

Eighth Embodiment In the above-described seventh embodiment, the method of arbitrarily selecting a fixed table having a plurality of different characteristics in the sixth embodiment according to the reception environment is changed to a method of configuring the table with a general-purpose memory such as a RAM. Therefore, the conversion characteristic can be freely changed by an external control means such as a CPU.

By the way, when the RAM is controlled by using an external control means such as a CPU, the above-mentioned power level information is generated by using the CPU and the RAM, and the power level used in each of the above-mentioned embodiments. The limiting circuit 13 and the power level increasing circuit 14 can be omitted.

Therefore, in the following eighth embodiment, the RAM is provided with the function of changing not only the conversion characteristics of the power level information but also the power multiplying factor and the power limit value. The case where the function of the increasing circuit is substituted for the RAM to reduce the circuit is shown.

FIG. 14 is a block diagram showing a soft decision Viterbi decoding apparatus according to the eighth embodiment of the present invention. In the eighth embodiment, the first non-linear conversion table RAM 20 in the configuration of the seventh embodiment shown in FIG. 13 is changed to C
It is a second non-linear conversion table RAM 22 that is a storage unit that is added with the functions of the power level limiting circuit and the power level increasing circuit by being controlled by the control unit such as PU. RAM for table
A CPU 21 that is a control unit that controls the CPU 22 is installed. Further, in FIG. 14, the power level limiting circuit 1
3 and power level increase circuit 14 are not present. Other configurations are similar to those shown in the seventh embodiment.

Next, the operation will be described. In the following description, description of the same operations as those in the seventh embodiment will be omitted, and only operations different from or added to the seventh embodiment will be described.

RAM 22 for the second nonlinear conversion table
Physically, the RAM is a storage unit that can freely rewrite the stored contents similarly to the RAM 20 for the first nonlinear conversion table that replaces the output result of the pilot signal amplitude comparison circuit 5 with the power level information in the seventh embodiment. Has the function of. However, the RAM 20 of the seventh embodiment
In the above, while only having the function of performing the non-linear conversion, the present embodiment also has the functions of the power limiting process and the power multiplying process. Therefore, in this embodiment, the power level limiting circuit 13 and the power level increasing circuit 14 used in the seventh embodiment are deleted from the configuration.

FIG. 15 is a diagram showing an example of characteristics set in the second non-linear conversion table RAM 22 of the eighth embodiment.

In FIG. 15, first, the comparison result of the pilot signal amplitude comparison circuit 5 is input as Pout.
It is shown by the first-order broken line indicated by the characteristic of = P. here,
For example, the power level information is multiplied by α (Pout = α × P)
In addition, the non-linear characteristic as used in the fifth embodiment is set in the RAM by limiting with a predetermined value, and the characteristic is shown by a solid line.

The solid line portion in FIG. 15 shows the non-linear conversion characteristic in which the power level information is almost "0" when the demodulation pilot signal has a small amplitude, that is, Ps indicating a signal with low reliability.
The power level information characteristic of α times (α times characteristic) and the power limiting characteristic indicating the limit value are composite characteristics that are switched in accordance with the input data. By setting such a characteristic curve by the CPU 21, not only the non-linear conversion operation but also the power level information limiting process and power multiplying process performed in the power level limiting circuit 13 and the power level increasing circuit 14 can be performed in the second manner. RAM 22 for non-linear conversion table
It can be done internally at the same time.

The CPU 21 uses the transmission system detection circuit 15 and the B
The RA for the second non-linear conversion table is judged so as to judge the contents of the ER detection circuit 16 and improve the receiving ability such as the BER value.
Rewrite the conversion characteristics set in M22.

As a method of determining the contents of the transmission system detection circuit 15 and the BER detection circuit 16 by the CPU 21, for example, by providing a read register or the like inside the transmission system detection circuit 15 and the BER detection circuit 16, each detection circuit Data can be read from the. The CPU 21, for example, always monitors the current transmission method such as the carrier modulation method from the transmission method detection circuit 15 and monitors the BER value from the BER detection circuit 22 as a register output during a period in which a reception signal is input. To do so. The CPU 21 can detect the current transmission method and reception performance (BER value) by performing the above monitoring.

The CPU 21, which has detected the current transmission method,
For the second non-linear conversion table RAM 22, a characteristic in which the receiving performance is most improved (for example, as shown in FIG.
5)). It should be noted that the characteristics used in the present embodiment are obtained in advance by the reception performance measurement experiment or the like for each transmission method. Further, the CPU 21
From the ER detection circuit 22, the current actual reception performance (BER
Value) can be detected and the detection result is fed back to the above-mentioned set characteristics, whereby the reception performance can be further improved.

As described above, in the present embodiment, the RAM is controlled by using the external control means such as the CPU, the power level information is generated, the power level limit value is changed, and the power level is increased. Since the function of changing the magnification can be provided, the power level limiting circuit and the power level increasing circuit, which are necessary in the other embodiments described above, can be eliminated, and the circuit scale can be reduced. .

[0149]

As described above, according to the soft-decision Viterbi decoding apparatus of the present invention described in claim 1, a power level limiting circuit for performing a power limiting process with an arbitrary value in the received power level information, and a power limiting A power level increasing circuit for multiplying the received power level information after processing by an arbitrary constant is provided, and weighting is performed not by the power level information of the demodulated received signal itself but by the converted power level information output from the power level increasing circuit. Since the function is provided, both circuits are appropriately controlled according to various transmission signal parameter changes and input power level information that changes depending on the reception environment.
It becomes possible to adjust the intermediate value information amount of the metric value, and as a result, there is an effect that it can be converted into power level information that minimizes the error rate at the time of Viterbi decoding, and the reception performance can be improved as compared with the conventional case.

According to the soft-decision Viterbi decoding device of the present invention described in claim 2, a transmission system detection circuit for detecting system transmission signal parameter information such as a carrier modulation system to be received and a coding rate is provided. , The function of controlling the power level limiting circuit and the power level increasing circuit based on the detection result is provided, so that the actual transmission signal parameter to be received can be detected. For example, the optimum power for each transmission signal parameter can be detected in advance. By determining the limit value and the power multiplication value, it becomes possible to perform optimum control for each detected transmission signal system, and it is possible to obtain optimum reception performance for each transmission signal system.

According to the soft-decision Viterbi decoding device of the present invention as defined in claim 3, a BER detection circuit for detecting the bit error rate value after the Viterbi decoding process is provided, and the power is detected based on the detection result. Since the function of controlling the level limiting circuit and the power level increasing circuit is provided, the actual transmission environment to be received (reception performance according to the BER value) can be detected, and both the above processing circuits are controlled based on the detection result. By that,
Even when the reception environment changes, it is possible to flexibly obtain optimum reception performance.

According to the soft-decision Viterbi decoding device of the present invention described in claims 4 and 5, both the transmission system detection circuit and the BER detection circuit are provided, and the system detected by the transmission system detection circuit is normally used. The power level limiting circuit and the power level increasing circuit are selectively controlled according to the contents of the transmission signal parameter and the control contents of the power level limiting circuit and the power level increasing circuit are modified depending on the detection content of the BER detection circuit. Since the function is provided, it is possible to detect the actual transmission signal parameter to be received and the reception environment at the same time, and it is possible to flexibly obtain optimum reception performance even if the transmission signal system is switched and the reception environment changes with time. .

Further, according to the soft-decision Viterbi decoding apparatus of the present invention described in claim 6, a non-linear conversion table for power level generation for generating power level information having a nonlinear characteristic is provided, and the output after conversion is provided. , The power level limiting circuit and the power level increasing circuit are controlled, and the function to use the multi-valued metric weighted by the non-linearized power level information is provided. In the case of data with low signal reliability, the generated power level information is biased to 0 as compared with the linear power level information using a linear conversion table using a linear curve, and the metric value of the demodulated signal with low reliability Can be set to an intermediate value between “0” and “1”, and the influence on the Viterbi decoding by the demodulated signal which is considered to have low reliability is minimized and the reliability is high. By using the demodulated signal more effectively, the error correction capability of the Viterbi decoder can be further improved.

Further, according to the soft decision Viterbi decoding apparatus of the present invention as defined in claim 7, a plurality of power level generating non-linear conversions having a plurality of conversion characteristics for generating power level information when a received signal is demodulated. Based on the results of the transmission method detection circuit and the BER detection circuit, control of switching between a plurality of types of tables is performed at the same time as the control of the power level limiting circuit and the power level increasing circuit, so that the error correction capability of the received data is increased. Since a function is provided, the optimum nonlinear conversion can be performed in various environments in which both the reception environment and the transmission signal system of the system that can be determined by the output of the transmission system detection circuit and the reception environment that can be determined by the output of the BER detection circuit are switched. A table can be used to control power limits and power scaling, and nonlinear multiple conversion tables for power level generation with optimal characteristics. By performing Le of control and at the same time, it is possible to further improve the error correcting capability of a Viterbi decoder.

Further, according to the soft-decision Viterbi decoding apparatus of the present invention described in claim 8, the table having the conversion characteristic for generating the power level information when the received signal is demodulated is configured by a general-purpose memory or the like. However, the function of rewriting the contents of the memory (table) from the outside of the CPU or the like to arbitrarily change the conversion characteristic is provided, and the conversion characteristic can be freely read / read from the configuration that supports a plurality of fixed tables in which the power conversion characteristic is written. Since it is changed to a table that uses a general-purpose memory that can be written, it is possible to flexibly generate power level information with arbitrary conversion characteristics that are optimal for the receiving environment at any timing, instead of selecting it. The error correction capability of the Viterbi decoder can be improved more flexibly. In addition, since the plurality of tables can be replaced with one general-purpose memory for implementation, the circuit scale of the soft-decision Viterbi decoding device can be reduced, and the circuit cost of the decoding device can be reduced.

According to the soft-decision Viterbi decoding apparatus of the present invention as defined in claim 9, the table having the conversion characteristic for generating the power level information is constituted by a general-purpose memory such as RAM, In addition to the function of giving a nonlinear conversion characteristic to, the function of changing the power multiplying factor and the power limit value is provided, so that the functions of the power level limiting circuit and the power level increasing circuit can be substituted for the RAM, and the soft decision can be made. The circuit scale of the Viterbi decoding device can be further reduced, and the circuit cost of the decoding device can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a soft-decision Viterbi decoding device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of reception on a constellation of 64QAM used for digital broadcasting.

FIG. 3 is an explanatory diagram showing a state of input power level information during multi-pass.

FIG. 4 is an explanatory diagram showing a state of output power level information when the control of the first embodiment is added to the input power level information at the time of multipath.

FIG. 5 is a block diagram showing a configuration of a soft decision Viterbi decoding device according to a second embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a soft-decision Viterbi decoding device according to a third embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a soft decision Viterbi decoding device according to a fourth embodiment of the present invention.

FIG. 8 is a block diagram showing the configuration of a soft decision Viterbi decoding device according to a fifth embodiment of the present invention.

FIG. 9 is a diagram showing characteristics of a power level generating linear conversion table.

FIG. 10 is a diagram showing a characteristic example of a power level generating nonlinear conversion table.

FIG. 11 is an explanatory diagram showing a state of output power level information when the control of the fifth embodiment is added to the input power level information at the time of multipath.

FIG. 12 is a block diagram showing the configuration of a soft-decision Viterbi decoding device according to a sixth embodiment of the present invention.

FIG. 13 is a block diagram showing the configuration of a soft-decision Viterbi decoding device according to a seventh embodiment of the present invention.

FIG. 14 is a block diagram showing the configuration of a soft-decision Viterbi decoding device according to an eighth embodiment of the present invention.

FIG. 15 is a diagram showing an example of characteristics set in a second non-linear conversion RAM.

FIG. 16 is a block diagram showing a conventional digital broadcast receiving system.

FIG. 17 is a block diagram showing a configuration of a conventional soft-decision Viterbi decoding device.

[Explanation of symbols]

1 digital demodulator, 2 deinterly
B, 3 Viterbi decoder, 4 Reed-Solomon decoder, 5 pilot signal amplitude comparison circuit, 6 pilot signal phase comparison circuit, 7 I, Q signal generation linear conversion table, 8 power level generation linear conversion table, 9 temporary determination circuit, 10 Metric arithmetic circuit,
11 multiplier, 12 conversion circuit, 13 power level limiting circuit, 14 power level increasing circuit, 15 transmission method detection circuit, 16 BER detection circuit, 17 power level generation nonlinear conversion table, 18 power level generation multiple nonlinear conversion table, 19 plural table selection circuit, 20 first non-linear conversion table RA
M, 21 CPU, 22 RAM for second non-linear conversion table.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04L 1/00 H04L 1/00 CF term (reference) 5B001 AA10 AB05 AC03 AC05 AD04 AE07 5J065 AA01 AB01 AC02 AD10 AE06 AF02 AG05 AG06 AH03 AH15 AH21 5K014 AA01 BA10 EA08 FA11 GA02 HA10 5K022 DD01 DD32

Claims (9)

[Claims] 1. A soft-decision Viterbi decoding device for performing weighting processing on multi-valued metric data using received power level information detected when demodulating a received signal of an OFDM modulation system, wherein the received power level information A power level limiting circuit that limits the received power level information to a predetermined value, and a power level increasing circuit that increases the received power level information limited by the power level limiting circuit by a predetermined scale factor. A soft-decision Viterbi decoding device characterized by using output received power level information. 2. A carrier modulation mode from the received signal,
A transmission method detection circuit for detecting at least one transmission method of a convolutional coding rate and a reception mode is provided, and the power level limiting circuit controls a predetermined value based on an output of the transmission method detection circuit. The soft decision Viterbi decoding apparatus according to claim 1, wherein the power level increasing circuit controls a predetermined scaling factor. 3. A BER detection circuit for detecting a bit error rate (BER) value from a Viterbi-decoded received signal, wherein the power level limiting circuit controls a predetermined value based on the output of the BER detection circuit, The soft decision Viterbi decoding apparatus according to claim 1, wherein the power level increasing circuit controls a predetermined scaling factor. 4. A carrier modulation mode from the received signal,
Transmission method detection circuit for detecting at least one of a convolutional coding rate and a reception mode, and a BER for detecting a BER value from a Viterbi-decoded reception signal
The power level limiting circuit controls a predetermined value and the power level increasing circuit controls a predetermined magnification based on the output of the transmission method detection circuit and the output of the BER detection circuit. The soft decision Viterbi decoding apparatus according to claim 1. 5. When the detection result of the BER detection circuit is less than a predetermined value, the power level limiting circuit and the power level increasing circuit perform control based only on the output of the transmission method detection circuit, When the detection result of the BER detection circuit is greater than or equal to a predetermined value, the power level limiting circuit and the power level increasing circuit output the BE of the transmission method and the BE.
The soft-decision Viterbi decoding device according to claim 4, wherein the control is performed based on an output of the R detection circuit. 6. A non-linear conversion table for power level generation for converting received power level information detected when demodulating a received signal using a non-linear conversion characteristic, wherein the power level limiting circuit is non-linear for the power level generation. The soft decision Viterbi decoding apparatus according to claim 4, wherein the received power level information converted by the conversion table is limited to a predetermined value. 7. The non-linear conversion table for power level generation includes a plurality of non-linear conversion tables for power level generation having a plurality of conversion characteristics, and the conversion based on the output of the transmission method detection circuit and the output of the BER detection circuit. 7. The soft-decision Viterbi decoding device according to claim 6, further comprising a plurality of table selection circuits for selecting characteristics. 8. A storage unit capable of rewriting arbitrary data, wherein the storage unit stores the plurality of nonlinear conversion tables for power level generation by a control device that controls a soft-decision Viterbi decoding device. The soft-decision Viterbi decoding device according to claim 7. 9. The storage unit stores, in addition to the conversion characteristic, power limit information for limiting the received power level information to a predetermined value and the received power level information limited to the predetermined value by a predetermined scale factor. And stores the power amplification information to be increased by the control device, wherein the control device selects the nonlinear conversion characteristic, the power limitation information, and the power amplification information based on the output of the transmission method detection circuit and the output of the BER detection circuit. The soft-decision Viterbi decoding device according to claim 8.