KR20130088638A - Equalizer for hierarchically modulated signal - Google Patents

Equalizer for hierarchically modulated signal Download PDF

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KR20130088638A
KR20130088638A KR1020120010009A KR20120010009A KR20130088638A KR 20130088638 A KR20130088638 A KR 20130088638A KR 1020120010009 A KR1020120010009 A KR 1020120010009A KR 20120010009 A KR20120010009 A KR 20120010009A KR 20130088638 A KR20130088638 A KR 20130088638A
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South Korea
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layer
signal
layer symbol
value
equalizer
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KR1020120010009A
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Korean (ko)
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임형수
김흥묵
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한국전자통신연구원
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

Abstract

The present invention relates to an equalizer for a hierarchical modulated signal in a digital broadcasting system.
According to an embodiment of the present invention, a hierarchical modulated signal equalizer comprising a forward filter, a first layer symbol detector, and a feedback filter is provided. The forward filter filters the hierarchical modulated signal to produce a forward filter output signal. The first layer symbol detector detects a first layer symbol value in the first layer symbol detector input signal. The feedback filter generates a feedback filter output signal by filtering the first layer symbol value plus the second layer symbol value. Here, the first layer symbol detector input signal is the sum of the forward filter output signal and the feedback filter output signal, and the tap coefficient of the forward filter and the tap coefficient of the feedback filter are the values of the first layer symbol detector input signal and the first layer symbol. The value is updated based on an error signal obtained by comparing a value obtained by adding a value of a second layer symbol.

Figure P1020120010009

Description

Equalizer for hierarchically modulated signals {EQUALIZER FOR HIERARCHICALLY MODULATED SIGNAL}

The present invention relates to an equalizer in a digital broadcast system, and more particularly to an equalizer for hierarchical modulated signals.

In Digital Video Broadcasting-Terrestrial (DVB-T), a transmission standard for terrestrial digital TV broadcasting signals in Europe, non-uniform constellations (non-uniformity) as shown in FIGS. -uniform constellation is adopted. In addition, DVB-S2 (Digital Video Broadcasting-Satellite-Second Generation), Europe's second-generation satellite broadcast signal transmission standard, is designed to improve transmission capacity while maintaining compatibility with DVB-S, a first-generation satellite broadcast signal transmission standard. A nonuniform constellation as shown in FIG. 2 was adopted. The non-uniform constellation adopted by these two standards is a hierarchical modulation technique, and the transmitter synchronizes a first layer (base layer) signal and a second layer (additional layer) signal having different signal powers to obtain the same antenna. Simultaneously transmits the signal, and the receiver receives the hierarchical modulated signal and restores both the first layer signal and the second layer signal or only the first layer signal according to the reception environment and conditions.

In addition, the AT-DMB (Advanced Terrestrial-Digital Multimedia Broadcasting) system, which improves the transmission efficiency of the T-DMB (Terrestrial-Digital Multimedia Broadcasting) system, applies a hierarchical modulation technique as shown in FIG. It is possible to provide services of high quality and transmission efficiency while maintaining compatibility.

In addition, ATSC (Advanced Television System Committee) system, which is a U.S. terrestrial broadcasting standard, applies hierarchical modulation technology together with high-performance channel coding technology having a low coding rate to increase transmission capacity while minimizing the impact on existing broadcasting services. A transmission and reception technique has been developed.

Among the above-described transmission systems to which the hierarchical modulation technique is applied, receivers in the ATSC system and the AT-DMB system that have advanced transmission capacities detect a first layer signal using an existing receiver structure, and the first layer detected in the received signal. The signal is removed to detect the second layer signal. However, in the case of AT-DMB receiver, unlike conventional receiver, coherent demodulation technique is applied.

However, if the entire layer modulated signal including the first layer signal and the second layer signal can be received in an optimized reception method, the reception performance may be further improved. In particular, when the ratio of the second layer signal power to the first layer signal power is high, the optimized reception method considering the characteristics of the full layer modulated signal is more effective.

The present invention provides an equalizer for hierarchical modulated signals.

The present invention provides a channel equalization method reflecting characteristics of a hierarchical modulated signal.

The present invention provides an apparatus and method for receiving a hierarchical modulated signal.

According to an embodiment of the present invention, a hierarchical modulated signal equalizer comprising a forward filter, a first layer symbol detector, and a feedback filter is provided. The forward filter filters the hierarchical modulated signal to produce a forward filter output signal. The first layer symbol detector detects a first layer symbol value in the first layer symbol detector input signal. The feedback filter generates a feedback filter output signal by filtering the first layer symbol value plus the second layer symbol value. Here, the first layer symbol detector input signal is the sum of the forward filter output signal and the feedback filter output signal, and the tap coefficient of the forward filter and the tap coefficient of the feedback filter are the values of the first layer symbol detector input signal and the first layer symbol. The value is updated based on an error signal obtained by comparing a value obtained by adding a value of a second layer symbol.

According to the present invention, an equalizer reflecting the characteristics of the hierarchical modulated signal is provided.

Thus, the performance of the apparatus for receiving hierarchical modulated signals is improved.

1A to 1D are examples of non-uniform constellations in DVB-T and satellite broadcast signal transmission standards.
2 is an example of non-uniform constellations in DVB-S2.
3 is an example of hierarchical modulation in AT-DMB.
4 shows an example of an 8-level baseband symbol in an ATSC system.
5 is an example of a hierarchical modulated signal in an ATSC-based transmission efficiency enhancement system.
6 is an example of a block diagram illustrating a structure of a transmitter for generating a hierarchical modulated signal in an ATSC based transmission efficiency enhancement system.
7 is an example of a block diagram illustrating a structure of a receiver for receiving a signal in an ATSC based transmission efficiency enhancement system.
8 is an example of a block diagram illustrating a structure of a DFE included in a receiver in an ATSC system.
9 is an example of a block diagram illustrating a structure of a DFE including a first layer symbol detector.
10 is an example of a block diagram illustrating a structure of a receiver including a DFE including a first layer symbol detector.
11 is an example of a block diagram illustrating a structure of a receiver including a first layer symbol detector including a TCM decoder.
12 and 12A are examples of block diagrams illustrating the structure of an equalizer using a first layer symbol value and a second layer symbol value.
13 and 14 are examples of block diagrams illustrating a structure of a receiver including an equalizer using a first layer symbol value and a second layer symbol value.
15 and 15A are examples of block diagrams illustrating a structure of an equalizer including a second layer symbol detector.
16 is an example of a block diagram illustrating a structure of a receiver including an equalizer including a second layer symbol detector.

Hereinafter, in order to facilitate explanation and avoid unnecessary repetition, channel equalization techniques will be described based on an advanced television system committee (ATSC) based transmission efficiency enhancement system. However, the present invention is not limited to the above system, and those skilled in the art may easily apply the technical idea of the present invention to other systems.

The 8-level baseband symbols specified in "ATSC Digital Television Standard Part 2-RF / Transmission System Characteristics (A / 53, Part 2: 2007)" published in January 2007 are shown in FIG. , -5, -3, -1, +1, +3, +5, +7}. At this time, the average power of the 8-level signal is 21.

In order to improve the transmission capacity while having compatibility with the ATSC-based conventional terrestrial broadcasting system, as shown in FIG. 5, a hierarchical modulation technique that adds a two-level signal having very small power around each symbol level of FIG. 4 is used. 16 levels in total (-7-δ, -7 + δ, -5-δ, -5 + δ, -3-δ, -3 + δ, -1-δ, -1 + δ, + 1- δ, + 1 + δ, + 3-δ, + 3 + δ, + 5-δ, + 5 + δ, + 7-δ, + 7 + δ) may be used. Here, the power of the first layer signal is 21 and the power of the second layer signal is δ 2 .

6 is an example of a block diagram illustrating a structure of a transmitter for generating such a hierarchical modulated signal. Referring to FIG. 6, a first layer encoder (layer 1 FEC encoder) 610 performs channel encoding on first layer data, and a first layer mapper 620 is channel encoded. The first layer signal is symbol-mapped to generate a first layer signal. The second layer encoder (layer 1 FEC encoder) 630 channel-codes the second layer data (layer 2 data), and the second layer mapper (layer 2 symbol mapper) 640 symbolizes the channel-coded second layer data. Mapping generates a second layer signal. The insertion level adjusting unit 650 multiplies the second layer signal with an appropriate weight according to the injection level of the second layer signal, and the adder 660 adjusts the first layer signal to the second layer. Add a signal The modulator 670 generates a baseband transmission signal by modulating a mixed signal of the first layer signal and the second layer signal.

In the case of the ATSC system, a channel code in which a RS code (Reed-Solomon code) and a Trellis-Coded Modulation (TCM) are interposed between an interleaver is used as a channel code of a first layer. (Vestigial Side Band) modulation scheme is used. In addition, in the ATSC-based transmission efficiency enhancement system, a channel code different from the channel code of the first layer such as a low-density parity check (LDPC) code may be used as the channel code of the second layer. In this case, the second layer mapper The appropriate weight multiplied by the second layer signal generated at is determined by the square root of the power ratio for the first layer signal of the second layer signal. For example, if the power of the second layer signal is 30 dB less than the power of the first layer signal, the weight multiplied by the second layer signal is about 0.0316.

7 is an example of a block diagram illustrating a structure of a receiver that receives a signal in such an ATSC-based transmission efficiency enhancement system.

After performing demodulation and channel equalization on the received hierarchical modulated signal, the process of restoring the first hierarchical data by demapping and channel decoding the first hierarchical signal is the same as that of the conventional ATSC system.

On the other hand, since the first layer signal and the second layer signal are independent of each other, the two layer signals act as interference to each other in the detection step of each layer signal. Since the first layer signal has a relatively larger power than the second layer signal, the interference effect due to the second layer signal is not large, but the second layer signal has a large interference effect due to the first layer signal. Accordingly, the first layer signal can be detected through a signal detection method in an existing ATSC system, but the second layer signal is detected through a method of removing the first layer signal from the layer modulated signal in order to secure detection performance. . That is, the second layer signal is obtained by subtracting the first layer symbol value determined by the layer 1 symbol demapper 730 from the output signal value of the equalizer 720.

The second layer data is recovered by demapping and channel decoding the second layer signal obtained through the above-described process.

On the other hand, the equalizer 720 of FIG. 7 uses a field sync pattern as a training sequence for a field sync signal corresponding to a preamble of a transmission frame structure in an ATSC system. A data-aided channel equalization technique is applied, and a decision feedback equalizer (DFE) technique is applied to the remaining data field signals except for the field sync signal.

8 is an example of a block diagram illustrating a structure of a DFE included in a receiver in an ATSC system. Referring to FIG. 8, the DFE includes a forward filter 810, a symbol detector 820, and a feedback filter 830.

The output signal of the demodulator passes through the forward filter 810, and the value of one of {-7, -5, -3, -1, +1, +3, +5, +7} by the symbol determiner 820. Is determined. In this case, the symbol determiner 820 may include a TCM decoder to increase the reliability of symbol determination. The output signal of the symbol determiner 820 is added back to the output signal of the forward filter 810 via the feedback filter 830.

Meanwhile, tap coefficients of the forward filter 810 and the feedback filter are updated based on an error signal obtained by comparing the input signal value and the output signal value of the symbol determiner 820. When the tap coefficients of the forward filter 810 and the feedback filter 830 converge to a constant value through the repetition of the above process, the transfer function of the DFE approaches the inverse of the impulse response of the channel. Therefore, the channel distortion can be compensated, and the input signal of the symbol determiner 820 becomes an output signal of the equalizer, and is restored to the transmission data through a demapping process and a channel decoding process.

Even in an ATSC-based transmission efficiency enhancement system, the first layer data may be restored by applying the DFE technology. In this case, as described above with reference to FIG. 7, the second layer data is recovered by removing the first layer signal from the output signal of the equalizer, detecting the second layer signal, and then demapping and channel decoding.

On the other hand, as shown in Figure 7, to obtain the second layer signal, the first layer symbol value determined by the first layer demapper can be subtracted from the output signal value of the equalizer, DFE included in the receiver in the ATSC system The receiver may be implemented by using a symbol determiner included in the first layer symbol detector. 9 is an example of a block diagram illustrating a structure of a DFE including a first layer symbol detector, and FIG. 10 is an example of a block diagram illustrating a structure of a receiver including such a DFE. That is, when the first layer symbol value is output from the DFE, the receiver may be configured as shown in FIG. 10.

However, since the first layer signal has a relatively larger power than the second layer signal, when the first layer symbol value is incorrectly detected, the first layer signal is subtracted from the output signal value of the equalizer. The reliability of the acquisition process is greatly worsened. Therefore, the TCM decoder can be used to increase the reliability of the first layer symbol detection. 11 is an example of a block diagram illustrating a structure of a receiver including a first layer symbol detector including a TCM decoder. In addition, in order to save time for restoring data, a TCM decoder having a short trace-back depth may be used without performing all channel decoding processes.

Meanwhile, the performance of the equalizer may be improved in consideration of characteristics of the hierarchically modulated received signal. That is, more accurate symbol determination using not only the first layer symbol value determined as one of {-7, -5, -3, -1, +1, +3, +5, +7} but also the second layer symbol value An error signal value can be obtained. In this case, the higher the ratio of the power of the second layer signal to the power of the first layer signal is, the higher the degree of improvement in channel equalization is. 12 and 12A are examples of block diagrams illustrating the structure of an equalizer using a first layer symbol value and a second layer symbol value, and FIGS. 13 and 14 illustrate a first layer symbol value and a second layer symbol value. An example of a block diagram showing the structure of a receiver including an equalizer to be used.

12 and 12A, the equalizer includes a forward filter 1210, a first layer symbol detector 1220, and a feedback filter 1230.

The forward filter 1210 filters the demodulator output signal, that is, the hierarchical modulated signal demodulated by the demodulator, to generate a forward filter output signal. The first layer symbol detector 1220 detects a first layer symbol value in the first layer symbol detector input signal. In addition, the feedback filter 1230 generates a feedback filter output signal by filtering the first layer symbol value (FIG. 12) or the value obtained by adding the second layer symbol value to the first layer symbol value (FIG. 12A). Here, the first layer symbol detector input signal is the sum of the forward filter output signal and the feedback filter output signal.

Meanwhile, the tap coefficients of the forward filter 1210 and the feedback filter 1230 are based on an error signal obtained by comparing a first layer symbol detector input signal value with a first layer symbol value plus a second layer symbol value. Is updated. As mentioned above. When the tap coefficients of the forward filter 1210 and the feedback filter 1230 are converged to a constant value through the repetition of the above process, the transfer function of the equalizer approaches the inverse of the shock response of the channel.

The input signal of the first layer symbol detector 1220 becomes an output signal of the equalizer and is restored to the transmission data through the demapping process and the channel decoding process of the first layer signal.

In this case, the second layer symbol value is obtained from the second layer symbol demapper 1350 outside the channel equalizer as shown in FIG. 13, or detected by the second layer decoder 1460 outside the channel equalizer as shown in FIG. 14. The second layer codeword 1470 may be obtained from the second layer symbol mapper 1470 for symbol mapping the second layer codeword. The second layer symbol value obtained by the latter method has an advantage of high reliability, but has a disadvantage in that it takes a long time to acquire. Therefore, in the latter case, a delay may occur in the received signal processing by the time required in the second layer channel decoding / coding process.

Meanwhile, the structure of the receiver may be simplified by including a second layer symbol detector in the equalizer. 15 and 15A are examples of block diagrams illustrating the structure of an equalizer including a second layer symbol detector, and FIG. 16 is a block diagram illustrating a structure of a receiver including an equalizer including a second layer symbol detector. One example. In this case, the second layer symbol detector may include a TCM decoder to increase the reliability of the second layer symbol determination.

Claims (1)

A forward filter for filtering the hierarchical modulated signal to produce a forward filter output signal;
First layer symbol detector A first layer symbol detector for detecting a first layer symbol value in an input signal; And
And a feedback filter for generating a feedback filter output signal by filtering the value obtained by adding the second layer symbol value to the first layer symbol value.
The first layer symbol detector input signal is a sum of the forward filter output signal and the feedback filter output signal,
The tap coefficient of the forward filter and the tap coefficient of the feedback filter are error signals obtained by comparing a value of the first layer symbol detector input signal with a value of the first layer symbol plus the value of the second layer symbol. The layer modulated signal equalizer, characterized in that for updating based on.
KR1020120010009A 2012-01-31 2012-01-31 Equalizer for hierarchically modulated signal KR20130088638A (en)

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