KR100876560B1 - JAM symbol demapping method for cable downstream transmission and apparatus thereof - Google Patents

Abstract

The present invention is to perform QAM symbol demapping for 64 QAM mode and 256 QAM mode in the downstream transmission, the present invention for demodulating the symbol and demodulated symbols of the I, Q symbols corresponding to the amplitude information Separate the absolute value of the I and Q symbols corresponding to the sign bit and the bit information, extract the amplitude information by changing the positions of I and Q from the absolute values of the separated I and Q symbols, and extract the extracted amplitude information I and Q symbols. The set separation information can be extracted using the LSB and the code bits of the I and Q symbols. Accordingly, as the number of bits used for QAM modulation increases as in the past, the hardware complexity of memory and address encoding increases, the hardware area increases, and the difficulty of processing data at high speed can be solved. By extracting the bit signal directly from the symbol based on the constellation degree determined, it is very efficient in terms of hardware area, cost, processing speed, and scalability.

Description

JAM SYMBOL DEMAPPING METHOD AND ITS APPARATUS FOR DOWNSTREAM TRANSMISSION OF CABLE MODULATION

1 is a block diagram illustrating a downstream signal processing procedure of a cable transmission system;

2 is a block diagram for QAM symbol demapping for cable downstream transmission according to the present invention;

3 is a diagram illustrating a QAM symbol demapper including an amplitude information extractor and an aggregate separation information extractor according to the present invention;

4 shows a 64 QAM constellation in accordance with the present invention;

5A is a diagram for analyzing a 64 QAM constellation diagram in consideration of characteristics of bit information according to the present invention;

5B is a diagram showing 64 QAM bit information shown on the x-axis and y-axis according to the present invention;

6 illustrates a 256 QAM constellation diagram in accordance with the present invention;

7A is a diagram for analyzing a 256 QAM constellation diagram in consideration of characteristics of bit information according to the present invention;

7B is a diagram showing 256 QAM bit information shown on the x-axis and y-axis according to the present invention;

8 is a table showing the relationship between c3, c0 and c1, c2 according to the present invention;

9 is a table showing the relationship between c4, c0 and c5, c1 according to the present invention.

<Description of the code | symbol about the principal part of drawing>

21, 26: MPEG frame portion 22: FEC encoder portion

221: Reed Solomon Encoder 222: Interleaver

223: randomization unit 224, 229: data format unit

225, 230: differential encoder 226, 227, 231, 232: BCC part

228: 64 QAM Symbol Mapper Section 233: 256 QAM Symbol Mapper Section

23: QAM demodulator 24: QAM demodulator

25: FEC decoder unit 251: trellis decoder unit

2511: QAM symbol demapper 2511a: amplitude information extraction unit

2511b: set separation information extraction unit 252: inverse randomization unit

253: deinterleaver 254: Reed Solomon decoder

The present invention relates to a method and an apparatus for Quadrature Amplitude Modulation (QAM) symbol demapping for cable downstream transmission, and more particularly, to a QAM symbol decode for 64 QAM mode and 256 QAM mode for downstream transmission. The present invention relates to a method and apparatus for restoring a bit signal by performing mapping.

As is well known, downstream in a system for cable transmission is transmitted as defined in ITU-T Recommendations J.83, Annex B, and the downstream signal processing proceeds as shown in FIG.

1 is a block diagram illustrating the downstream signal processing of the cable transmission system, and includes an MPEG frame unit 1, an FEC encoder unit 2, a QAM modulator 3, and a QAM demodulator ( 4), FEC decoder section 5, and MPEG frame section 6 are included.

The MPEG frame section 1 frames the MPEG-2 data stream input in units of packets and provides it to the FEC encoder section 2.

The FEC encoder section 2 applies a forward error correction algorithm to the MPEG-2 data stream framed by the MPEG frame section 1 to obtain a reliable FEC codeword corresponding to the channel to the QAM modulation section 3. to provide.

The QAM modulator 3 transmits the RF signal modulated by QAM with respect to the FEC codeword provided from the FEC encoder unit 2 through the cable channel S1.

Next, the downstream demodulation is performed through the QAM demodulation section 4, the FEC decoder section 5, and the MPEG frame section 6 in a process opposite to the modulation.

However, as described above, the conventional QAM symbol demapping method for performing a demodulation function downstream by the FEC decoder unit 5 uses a memory (not shown) to find bit information corresponding to an input symbol. To recover the bit signal. That is, when using memory, the memory address value should be designated according to the input symbol value. Since the symbol value includes a sign, not only the address encoding process is required but also the memory and address increases as the number of bits used for QAM modulation increases. The hardware complexity of encoding increases.

In other words, the use of memory as in the prior art not only increases hardware complexity but also has a limitation in memory access time, which makes it unsuitable for high-speed data transfer systems. Given the rapidly evolving environment of information and communication technology, QAM symbol demapping for 64 QAM mode and 256 QAM mode without memory can be applied for high speed data transmission system while reducing hardware complexity in downstream transmission. There is a need to further develop methods and apparatus that can be performed.

Accordingly, the present invention has been made in view of the necessity as described above, and an object thereof is to provide a cable downstream transmission that can be restored to a bit signal by performing QAM symbol demapping for 64 QAM mode and 256 QAM mode during downstream transmission. A QAM symbol demapping method and apparatus therefor are provided.

In order to achieve the above object, according to the present invention, a bit signal input to a QAM symbol mapper at a transmitting end is converted into a symbol by a constellation diagram used for cable downstream transmission, and the converted symbol is transmitted through a QAM symbol demapper at a receiving end. A QAM symbol demapping method for cable downstream transmission to be restored to a signal, demodulating the transformed symbols, and demodulating the demodulated symbols into I and Q symbols corresponding to amplitude information and I and Q symbols. Separating the absolute value of the symbol, extracting the amplitude information by changing the positions of I and Q from the absolute values of the separated I and Q symbols, and LSB, I, and Q symbols of the extracted amplitude information I and Q symbols. And extracting the set separation information using the sign bit.

In order to achieve the above object, the present invention, the bit signal input to the QAM symbol mapper at the transmitting end is converted into a symbol by the constellation diagram used for cable downstream transmission, and performs the QAM symbol demapping on the transformed demodulated symbol A device for demodulating a demodulated symbol into an absolute value of a sign bit of an I and Q symbol corresponding to amplitude information and an I and Q symbol corresponding to bit information, and an I and Q symbol from an absolute value of the separated I and Q symbols. An amplitude information extracting unit for extracting the amplitude information by changing the position of and a set separation information extracting unit for extracting the separation information by using the LSB and I and Q symbols of the extracted amplitude information I and Q symbols. It features.

Hereinafter, a plurality of embodiments of the present invention may exist, and a preferred embodiment will be described in detail with reference to the accompanying drawings. Those skilled in the art will appreciate the objects, features and advantages of the present invention through this embodiment.

2 is a block diagram for QAM symbol demapping for cable downstream transmission according to the present invention. The MPEG frame unit 21, the FEC encoder unit 22, the QAM modulation unit 23, and the QAM decoding A grand unit 24, an FEC decoder unit 25, and an MPEG frame unit 26 are included.

The MPEG frame unit 21 frames the MPEG-2 data stream input in units of packets and provides it to the FEC encoder unit 22.

The FEC encoder unit 22 uses a Reed-Solomon code having t error correction capabilities with respect to an outer coder using a concatenated coding technique, and uses an internal codeword. By using a Trellis coded modulation (TCM) codeword that produces a coded modulation code for the inner coder, an error that is not corrected at the inner decoder is corrected at the outer decoder to almost eliminate the error rate. As a block to be " 0 ", the Reed Solomon encoder 221, the interleaver 222, the randomizer 223, the data format units 224 and 229, and the differential encoder 225 230 And the BCC units 226, 227, 231, and 232, the 64 QAM symbol mapper unit 228, and the 256 QAM symbol mapper unit 233.

The Reed Solomon encoder 221 applies an RS block code to the MPEG-2 data stream framed by the MPEG frame unit 21, encodes it, and provides the encoded block to the interleaver 222. Here, the RS block code is composed of 128 symbols per block, of which only 122 symbols are information symbols and 6 symbols are parity for error correction, so that error correction is possible up to 3 symbols per RS block. The code is used equally in 64QAM mode and 256QAM mode.

The interleaver 222 is a block for coping with error symbols (e.g., burst errors) generated during channel transmission. The interleaver 222 is an MPEG-2 data stream encoded by the RS block code of the Reed Solomon encoder 221. The data stream rearranged by convolutional interleaving is provided to the randomizer 223. Here, the convolutional interleaving structure is a programmable structure in 64 QAM mode and 256 QAM mode and supports various interleaving modes.

The randomizer 223 randomizes the data interleaved by the interleaver 222 so as not to have a specific pattern, thereby preventing the RF-modulated signal from interfering with other channels and extracting synchronization from the receiver. By generating the pseudo noise code promised with the receiver and adding the input data, the data of the randomized 64 QAM mode is provided to the data format unit 224 and the data of the 256 QAM mode is provided to the data format unit 229. do.

The data format unit 224 formats the randomized 64 QAM mode data provided from the randomizer 223 to the TCM format, which is a channel encoding technique, and provides the differential coder unit 225 and the 64 QAM symbol mapper unit 228. do.

The differential encoder unit 225 encodes the 64 QAM mode data formatted according to the TCM format provided from the data format unit 224 into uncondensed bits having constellations with signal constellations invariant to 90 ° rotation. 226 and 227 to the 64 QAM symbol mapper unit 228.

64 QAM symbol mapper unit 228 is a convolutional code that matches the data format unit output bit signal of the coordinates rotated by 90 degrees of the data format unit output bit signal of arbitrary coordinates located in the first quadrant provided from the data format unit 224. Is identically set according to the x-axis and y-axis values irrespective of rotation of 90 ° according to the set partitioning characteristic of the TCM provided from one bit and the differential encoder unit 225 through the BCC units 226 and 227. Bits that are not repeated convolutional encoding are mapped and provided to the QAM modulator 23.

The data format unit 229 formats the randomized 256 QAM mode data provided from the randomizer 223 to the TCM format, which is a channel encoding technique, and provides the differential coder 230 and the 256 QAM symbol mapper 233. do.

The differential encoder unit 230 encodes the data of 256 QAM mode formatted according to the TCM format provided from the data format unit 229 into uncondensed bits having a constellation of the signal constellation having a 90 ° rotation invariant. 231 and 232 are provided to the 256 QAM symbol mapper unit 233.

The 256 QAM symbol mapper unit 233 is a convolutional code that matches the data format unit output bit signal of the coordinates rotated by 90 ° in the data format unit output bit signal of arbitrary coordinates located in the first quadrant provided from the data format unit 229. Is identical to the x-axis and y-axis values irrespective of rotation of 90 ° according to the set partitioning characteristic of the TCM provided from one bit and the differential encoder unit 230 through the BCC units 231 and 232. Bits that are not repeated convolutional encoding are mapped and provided to the QAM modulator 23.

The QAM modulator 23 performs a convolutional coded bit and non-convolutional bit information provided by being mapped from the 64 QAM symbol mapper 28 and the 256 QAM symbol mapper 233 in the FEC encoder unit 22. It is modulated by QAM and transmitted through cable channel S1.

Next, the QAM demodulator 24 demodulates the mapped convolutional coded bits and the nonconvolutional encoded bit information into QAM received through the cable channel S1 and provides the FEC decoder unit 25 with demodulation. .

The FEC decoder 25 includes a trellis decoder 251, an inverse randomizer 252, a deinterleaver 253 and a Reed Solomon decoder 254.

The trellis decoder 251 includes a QAM symbol demapper 2511 composed of an amplitude information extractor 2511a and an aggregate separation information extractor 2511b, as shown in FIG.

The amplitude information extractor 2511a is a block for extracting amplitude (e.g., phase) information. The amplitude information extractor 2511a extracts a symbol of convolutional coded bits and nonconvolutional coded bits provided and demodulated by the QAM demodulator 24. The code bit is separated into an absolute value, and the absolute value of the I and Q symbols is represented by Equation 1

The absolute value of the I and Q symbols is = (| · | -1) / 2, where ||| is the absolute value range of the I and Q symbols.

Through the function of, it can be represented by the bit information shown on the x-axis and y-axis of Fig. 5b or 7b, the signal corresponding to the absolute value of the I, Q symbols output in this process is called I_magnitude, Q_magnitude, amplitude In order to obtain bit information, the positions of I and Q are changed by using I and Q converters in the absolute values described above, so that the amplitude (phase) information, that is, the code bits of the I and Q symbols are exclusive logical sums (XOR). The amplitude information is extracted using the I_Q_change signal applied to the circuit and provided to the inverse randomizer 252.

Here, the method of extracting the amplitude information from the amplitude information extracting unit 2511a is a diagram showing a 64 QAM constellation diagram with reference to FIG. 4, where c3, c0 is a constellation diagram of set separation information, and the rest of 64 QAM. As c5, c4, c2, c1 is an amplitude information constellation diagram having invariance with 90 ° rotation, the amplitude information constellation diagram (c5, c4, c2, c1) of 64 QAM is extracted, and the bit information shown in FIG. Analyzing the amplitude information constellation in consideration of characteristics, it can be seen that c4 and c1 are amplitude information of I symbol and c5 and c2 are amplitude information of Q symbol in 64 QAM, and c3 and c0 are separate sets of I and Q symbols, respectively. As the constellation of the information, c3, c0 is repeated the same regardless of the 90 ° rotation, while LSB two bits c1, c2 are invariant to 90 ° rotation, so as shown in Figure 8 c3, c0 and The amplitude (phase) information of each symbol can be extracted based on c1 and c2. FIG. 8 is a table showing the relationship between c3, c0 and c1, c2. The sign bits of I and Q are represented by '0' when positive and '1' when negative.

As shown in FIG. 5B, the I signals of 64 QAM are c4 and c1, the Q signals are c5 and c2, and the absolute values of the I and Q symbols are 0, 1, 2 and 3 by these. According to the general constellation diagram, the size of the I, Q symbol value is 1,3,5,7 at 64 QAM, so by multiplying 2 and adding 1 to each of the above outputs (0,1,2,3), You can get the values (1, 3, 5, 7).

Likewise, referring to FIG. 6, in 256 QAM, c4, c0 is a constellation diagram of aggregation separation information, and the remaining c7, c6, c5, c3, c2, c1 are amplitude constellation diagrams having invariance with 90 ° rotation. When c7, c6, c5, c3, c2, c1 of the QAM are extracted and the constellation diagram is analyzed in consideration of the characteristics of the bit information shown in FIG. 7A, c7, c6, c5 at 256 QAM is amplitude information of I symbol and c3 , c2, c1 is the amplitude information of the Q symbol, c4, c0 is a set separation information of the I, Q symbols, respectively, c4, c0 is repeated the same regardless of the 90 ° rotation, LSB two bits c5, Since c1 has an invariance with respect to 90 ° rotation, as shown in FIG. 9, the amplitude (phase) information of each symbol may be extracted in a relationship of c4, c0 and c5, c1. Here, FIG. 9 is a table showing the relationship between c4, c0 and c5, c1, and the sign bits of I and Q are represented by '0' when positive and '1' when negative.

As shown in FIG. 7B, the I signals of 256 QAM are c7, c6, and c5, and the Q signals are c3, c2 and c1, whereby the absolute values of the I and Q symbols can be obtained. By multiplying each of the range of values by 2 and adding 1, the desired size of the I and Q symbol values can be obtained.

The aggregation separation information extracting unit 2511b is a block for extracting the TCM aggregation separation information, and according to the respective tables shown in FIGS. 8 and 9, the LSB and amplitude (phase) information of the amplitude information I and Q symbols are respectively determined. It can be restored by applying it to an exclusive OR circuit. That is, the LSB of the amplitude information I and Q symbols can be obtained by changing the positions of the I and Q symbols or reversing the negative values according to the amplitude (phase) information. The signal of which the positions of the I and Q symbols are changed is I_magnitude. And LS_ of Q_magnitude, i.e., I_magnitude [0] and Q_magnitude [0], so that the code bits of I and Q symbols corresponding to amplitude (phase) information are applied to the exclusive OR (circuit-wise) circuit to extract the set separation information. The reverse randomization unit 252 is provided.

Here, the method of extracting the aggregation information by the aggregation information extracting unit 2511b is a constellation diagram of aggregation information of c3, c0 in 64 QAM. Referring to FIG. 6, c4, As c0 is a constellation diagram of the aggregation separation information, c3, c0 of 64 QAM and c4, c0 of 256 QAM can be extracted.

The operations of the inverse randomization unit 252, the deinterleaver unit 253, the Reed Solomon decoder unit 254, and the MPEG frame unit 26 are described with the above-described MPEG frame unit 21 and the Reed Solomon encoder unit 221. The interleaver 222 and the randomizer 223 perform the reverse process.

Therefore, by performing QAM symbol demapping on the 64 QAM mode and the 256 QAM mode in the downstream transmission, and restoring the bit signal, the bit signal directly from the symbol based on a constellation diagram fixedly determined without using memory as in the past. Can be extracted.

In addition, since the present invention is disclosed as a right within the spirit and claims of the present invention, the present invention may include any modification, use and / or adaptation using general principles, and the present invention as a matter deviating from the description of the present specification. It includes everything that falls within the scope of known or customary practice in the art to which it belongs and falls within the scope of the appended claims.

As described above, according to the present invention, by performing QAM symbol demapping on the 64 QAM mode and the 256 QAM mode during the downstream transmission, and recovering the bit signal without using the memory, the present invention uses the memory as before. By adopting the QAM symbol demapping method to find the bit information corresponding to the symbol, it is necessary to specify the memory address value according to the input symbol value. Since the symbol value includes a sign, the address encoding process is required accordingly, and the QAM modulation is performed accordingly. As the number of bits used increases, the hardware complexity of memory and address encoding increases, the hardware area increases, and the difficulty of processing data at high speed can be solved.

In addition, in the present invention, since the bit signal is directly extracted from the symbol based on the constellation diagram determined in a fixed manner, it is very effective in terms of hardware area, cost, processing speed, and scalability.

Claims (8)

Bit signal input to the QAM symbol mapper at the transmitting end is converted into a symbol by a constellation diagram used for cable downstream transmission, and the converted symbol is recovered for the bit downstream through the QAM symbol demapper at the receiving end. As a QAM symbol demapping method, (a) demodulating the converted symbol, and separating the demodulated symbol into absolute values of I and Q symbols corresponding to bit information and I and Q symbols corresponding to amplitude information; (b) extracting amplitude information by changing positions of I and Q in absolute values of the separated I and Q symbols; (c) extracting set separation information by using the extracted LSBs of the amplitude information I and Q symbols and the sign bits of the I and Q symbols. RAM symbol demapping method for cable downstream transmission comprising a. The method of claim 1, The absolute values of the I and Q symbols in the step (a), Equation 1  (| · | -1) / 2 (where | · | is an absolute value range of I and Q symbols) A SAM symbol demapping method for cable downstream transmission, characterized in that it is represented by bit information via a function of. The method of claim 1, Extracting the amplitude information in the step (b), If the constellation is 64 QAM, Extracting the amplitude information constellation diagram among the set separation information constellation diagrams c3 and c0 of the constellation diagram and the amplitude information constellation diagrams c5, c4, c2 and c1; Analyzing amplitude information constellations in consideration of the characteristics of the bit information; Determining the I symbol amplitude information (c4, c1) and the Q symbol amplitude information (c5, c2) of the constellation diagram through the analysis; Extracting by using the relationship between the set separation information constellation and the I / Q symbol amplitude information (c1, c2) RAM symbol demapping method for cable downstream transmission comprising a. The method of claim 1, Extracting the amplitude information in the step (b), If the constellation is 256 QAM, Extracting the amplitude information constellation diagram (c7, c6, c5, c3, c2, c1) from the set separation information constellation diagram (c4, c0) and amplitude information constellation diagram (c7, c6, c5, c3, c2, c1) of the constellation map Process, Analyzing amplitude information constellations in consideration of the characteristics of the bit information; Determining the I symbol amplitude information (c7, c6, c5) and the Q symbol amplitude information (c3, c2, c1) of the constellation diagram through the analysis; Extracting by using the relationship between the set separation information constellation and the I / Q symbol amplitude information (c5, c1) RAM symbol demapping method for cable downstream transmission comprising a. An apparatus for converting a bit signal input from a transmitter into a QAM symbol mapper into a symbol by a constellation diagram used for cable downstream transmission, and performing QAM symbol demapping on the converted demodulated symbol, The demodulated symbol is divided into absolute values of I and Q symbols corresponding to bit information and I and Q symbols corresponding to amplitude information, and positions of I and Q in absolute values of the separated I and Q symbols. An amplitude information extracting unit for extracting amplitude information by An aggregation separation information extracting unit extracting aggregation separation information by using the extracted LSBs of the amplitude information I and Q symbols and the code bits of the I and Q symbols. Jam symbol demapping apparatus for cable downstream transmission comprising a. The method of claim 5, wherein The absolute value of the I, Q symbols, Equation 1  (| · | -1) / 2 (where | · | is an absolute value range of I and Q symbols) A SAM symbol demapping apparatus for cable downstream transmission, characterized in that it is represented by bit information via a function of. The method of claim 5, wherein The amplitude information extraction unit, I, Q converter (Changer) for changing the position of I and Q in the absolute value of the I, Q symbol, An exclusive-OR circuit for generating the code bits of the I and Q symbols into an I_Q_change signal. A SAM symbol demapping apparatus for cable downstream transmission, further comprising a. The method of claim 5, wherein The aggregation separation information extraction unit, And a two exclusive logical sum (XOR) circuit to extract the aggregate separation information.

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