KR100556448B1 - Method and apparatus for demapping - Google Patents

Abstract

The present invention relates to a method and apparatus for mapping a transmission data to a predetermined constellation according to a modulation method, and then demapping the received data by region when the transmitted data is received. Particularly, the values of the real and imaginary axis data are respectively input. By linearly dividing the region of the region, demapping to quantize the input channel state information value by the region discrimination value, the region discrimination only when the input data is linearly separated and forced when demapping the received data. Because it is not limited to, the reliability is improved by accurate domain classification, and when the channel status information value is too small, it is output to a certain value or when the channel status information is very small by forced soft decision. It is possible to prevent an error caused by the product of.

Description

Demapping method and apparatus {Method and apparatus for demapping}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Coded Orthogonal Frequency Division (COFDM) system using multiple carriers, and more particularly, to a method and apparatus for appropriately classifying received data and demapping them using the same.

Digital TV transmission can be classified into a single carrier modulation method using a single carrier and a multicarrier modulation method for transmitting desired data using a plurality of multiple carriers. . That is, the transmission method of the digital TV is divided into a residual side band (VSB) method using one single carrier and a COFDM method using a plurality of carriers.

The COFDM scheme using a plurality of multi-carriers has a feature that can easily recover the damage of the signal due to the multi-path channel, and unlike the conventional single carrier is one feature is also possible Single SF Network (SFN).

The COFDM performs error correction coding (FEC) on the transmission data to compensate for errors that may occur on the channel during transmission at the transmitting end, and then maps the data to a predetermined constellation according to a modulation method and transmits the same. In the reverse process, the received data is demapped, which is the opposite of mapping, and then FEC decoding is performed to correct an error that may occur in the channel. The modulation scheme mainly used in mapping at the transmitting end is Quadrature Phase Shift Keying (QPSK), Quadrature Amplitude Modulation (16-QAM), and 64-QAM.

That is, in order to transmit desired data by the COFDM method, the data is first mapped by one of the three modulation methods described above, subjected to an Inverse Fast Fourier Transform (IFFT), and then inserted by a guard interval. do. The transmitted data undergoes the reverse process of the transmitter at the receiver. First, it passes through the FFT and equalizer, and then is input to the demapper. The data is de-mapped in reverse according to the mapping method of the data transmitted from the demapper.

At this time, in order to demapping, first, the data output from the equalizer should be divided according to a predetermined constellation transmitted.

1 is a conventional method of classifying a region, which is disclosed in US Pat. No. 5,134,635.

FIG. 1 is a method of distinguishing a region at a receiving end when 4 bits are transmitted in 16-QAM including one symbol. The values of the real and imaginary transmission bits are respectively 10 according to -3, -1,1,3. An example of mapping to 11,01,00 is shown. That is, when transmitted in 16-QAM, since one symbol consists of 4 bits, two bits can be distinguished from each of the real axis and the imaginary axis.

Therefore, the first bit output b (n) of the real axis and the imaginary axis is output by the relationship of Equation 1 below.

b (1) or b (3) = -1 if z (n)> 1

= -z (n) if z (n) ≥ 0

= z (n) if z (n)> -1

= 1 otherwise

That is, it is determined whether the output signal z (n, k) (which represents the k-th carrier of the n-th symbol) of the equalizer is greater than 1 or less than -1. If it is greater than 1, this area determines that the first bit is transmitted as 0 and outputs -1. If less than -1, this area determines that the first bit is transmitted as 1 and outputs 1. In addition, the area of -1 to 1, which can be used as a boundary point between 0 and 1, causes the output of the equalizer to be displayed as it is, that is, the output of z (n, k) and -z (n, k), respectively.

In addition, the second bit of the real axis and the imaginary axis is output by the relationship of the following equation (2).

b (2) or b (4) = -1 if z (n)> 3

= 2- | z (n) | if | z (n) | ≥ 1

= 1 otherwise

The area discrimination value thus output is again calculated as a bit metric by the relationship of Equation 3 below, wherein y is received data.

m (k, 1) = yb (k) ² * CSI, y = 1

m (k, 0) = yb (k) ² * CSI, y = -1

Here, b (k) is one of domain-divided values, that is, 1, -1, z (n), -z (n), and 2- | z (n) |. That is, when channel state information (CSI) indicating the state information of each channel of each of the received data symbols is also input together with the data received by the demapping end, an area classification method as shown in Equation 3 above is performed. Is changed.

The bit metrics calculated by Equation 3 perform a hard decision that compares the size of each other to determine 1 and 0 for each bit.

However, in the above-described area discrimination method, when the value of the received data is 1 or -1 or more, the output is forcibly limited to -1 or 1 in the first bit area of the real and imaginary axes of the received data. To make a distinction. That is, if the received data value is 1 or more than -1 even though the degree of noise is different, it is artificially distorted without considering the difference. Therefore, it can be seen that the accurate region division is not made.

Similarly, the second bit of the real and imaginary axes has the same problem because the output is forcibly limited to -1 or 1 when the value of the received data becomes 3 or -3 or more or between 1 and -1. do.

In addition, when the decision process is performed after multiplying the area discrimination value by the channel state information, a hard decision is made when the value is greater than or equal to 1 and the value less than or equal to 0, which is a problem.

In addition, even when the channel state information value multiplied by the area discrimination value is too small, it is multiplied by the area discrimination value as it is, so that when the quantization is performed, the multiplication value of each other is too small to be quantized to a low value of 1 or 0. There is a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a demapping method for linearly outputting data without forcibly restricting the input data in a predetermined area or more when the area of the input data for demapping is divided. In providing.

Another object of the present invention is to provide a demapping apparatus for soft decision by a predetermined interval after multiplying an area division value by channel state information.

Still another object of the present invention is to provide a demapping apparatus for forcibly outputting a channel state information value to a value larger than a predetermined value when the channel state information value is input below a certain value.

The demapping method according to the present invention for achieving the above object, the mapping of the transmission data to a certain constellation according to the modulation method, and the value of the real and imaginary axis data received when the transmitted data is received, respectively Linearly dividing and outputting the region, and multiplying the received channel state information by the region division value of the step to perform quantization.

According to the present invention, the demapping apparatus maps transmission data to a certain constellation according to a modulation method, and when data transmitted through the FFT and the equalizer are input, the demapping apparatus determines the values of the real and imaginary axis data. An area detection unit for linearly dividing and outputting an area, a power calculation unit for receiving the channel state information of each QAM symbol as an input, calculating and normalizing signal power, and outputting this value as a channel state information value, and the area And a decision unit and a quantizer for multiplying the values divided by the respective areas by the detector and multiplying the channel state information values of the power calculator and quantizing the difference between the multiplied values.

When the channel state information value is smaller than a predetermined value, the channel state information is output as a value larger than a predetermined value and multiplied by the region division value.

When the channel state information value multiplied by the area division value is smaller than a predetermined value, the forced soft decision is performed to a predetermined value.

This demapping method and apparatus makes accurate region division and improves reliability. Also, when the channel state information value is too small, an error that may be caused by the channel state information value is too small by outputting it to a certain value or by soft soft decision. It can prevent.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a block diagram illustrating a demapping apparatus according to the present invention, in which an area detector 21 and a respective QAM symbol are used to distinguish the areas according to respective bits of a real axis and an imaginary axis of data output from an equalizer. The power calculator 22 calculates the signal power by receiving the CSI as an input, and applies the signal power for each symbol output from the power calculator 22 to the output of the area detector 21. Decision and quantization unit 23 for performing phase and quantization, internal deinterleaver 24 for symbol deinterleaving and bit interleaving for the quantized data, and 1 or 0 for internal deinterleaved data is determined. It consists of the Viterbi decoder 25.

Referring to FIG. 2 configured as described above, the value of each carrier output from the equalizer is input to a region detector 21. The area detector 21 outputs the output signal of the equalizer as the value of the required area according to each bit according to the transmitted constellation, and the value of each area is again calculated by a constant relational expression. Can be used as status information of bits 1 or 0.

3 is a graph illustrating a method of classifying the area of the area detector 21 according to the present invention. When the transmitter first maps data to 16-QAM, 4 bits of data constitute one QAM symbol, and one QAM symbol is 1. The example shows a case in which the second and third bits are allocated to the bits corresponding to the real axis, and the second and fourth bits are allocated to the bits corresponding to the imaginary axis.

That is, since the mapping stage transmits the bits 10, 11, 01, 11 of the real axis and the imaginary axis to -3, -1, 1, 3, and transmits them, the area detection unit 21 of the receiving end is shown in FIG. As shown, first, data corresponding to the first bit in each coordinate axis is divided into regions.

For example, when data is mapped at the transmitting end, 1 is transmitted for negative data mapping with a line of x = 0 and 0 is transmitted for positive data mapping. Therefore, as shown in FIG. 3, when the input data is divided by x based on a straight line of x = 0 and the input data is x and the output region division value is y, the relationship between the input and output is expressed by Equation 4 below.

y = -x

At this time, if the input value is greater than | 1 | as shown in FIG. 3, the linear reflection is continued without restricting it. This makes the method more effective than forcibly limiting it to 1 or -1 when larger than the conventional | 1 | (dotted line in Fig. 3).

4 is a graph illustrating a method of classifying a region of a second bit in each bit of a real axis and an imaginary axis. As for division of the second bit, since division of 1,0 of bits transmitted from the transmitter occurs at -2 and 2, as shown in FIG. 4, the value of input x is positive and the output area division is y. The input / output relationship is then expressed as shown in Equation 5 below.

y = -x + 2

In addition, when the input value of x is negative and the output area division value is y, the relationship between the input and output is expressed by Equation 6 below.

y = x + 2

Here too, when the value of x input is smaller than | 1 | or larger than | 3 |, the output is linearly reflected without limiting the output to 1 or -1.

The data thus input is converted by the area detector 21 and then input to the decision and quantizer 23.

Meanwhile, the power calculator 22 receives channel state information for each QAM symbol as an input, calculates signal power, normalizes it, and outputs the signal power to the decision and quantizer 23 using this value as a CSI value. do.

The decision and quantization unit 23 multiplies the output value of the area detection unit 21 with the CSI value of the power calculation unit 22 and then quantizes the difference between the multiplied values. This is because if the difference is quantized, the larger the difference is, the closer the value is to 1 or 0. That is, the product of the value of the CSI input to the decision and quantization unit 23 and the area division value of the area detection unit 21 is quantized into 8 or 16 sections.

At this time, in multiplying the output value of the area detector 21 with the CSI value, when the CSI value is too small below a certain value (c), as shown in FIG. 5, a constant value or larger value (d) And multiply by the area division value of the area detection unit 21. Or, if the CSI value is small, the channel state is very bad, and the soft decision is made to force the output to 3 or 4.

That is, the reason for doing this is that when the output value of the area detector 21 becomes a very large value, if the CSI value is too small, the product value of each other is too small when the quantization is performed at a subsequent stage, so that the reliability of 1 or 0 is small. Is quantized to a low value.

On the other hand, the larger the difference between the value of the area detector 21 and the CSI value, the larger the value of 1 or 0. Therefore, the larger the difference between each other, 1 or 0 gives a lot of weights. When quantization is performed, Viterbi decoding can be performed more efficiently by using information of each CSI.

That is, the output of the decision and quantization unit 23 is input to the Viterbi decoder 25 through the internal deinterleaver 24 including the symbol deinterleaver and the bit deinterleaver, so that the received data is finally demodulated.

FIG. 6 shows a method of distinguishing areas when data to be transmitted is transmitted by 64-QAM. When transmitting data in 64-QAM, 6 bits make up a symbol. When the order is y ₀ , y ₁ , y ₂ , y ₃ , y ₄ , y ₅ , the data on the real axis is y ₀ , y ₂ , y ₄ corresponds to the imaginary axis, and y ₁ , y ₃ , and y ₅ correspond to the data. In the case of 64-QAM, the first data and the second data of the real axis and the imaginary axis are divided according to the principle shown in FIGS. 3 and 4, as in the case of 16-QAM. The first bit of the axis and the imaginary axis is output as shown in Equation 4 above.

However, the second bit is represented by a relationship as shown in Equation 7 since the data of the mapping stage is extended from -7 to 7.

y =-| x | +4

In addition, the third bit output of the real axis and the imaginary axis is a little more complicated as shown in Fig. 6, and when the value of the input x is smaller than | 4 |, it is expressed by Equation 8 below.

y = | x |-2

When the value of x is larger than | 4 |, it is expressed as in Equation 9 below.

y =-| x | + 6

At this time as well, the output of the area detection unit 21 is limited to -1 or 1 and is not outputted to reflect the difference in distance.

7 and 8 are graphs of simulation results by the above-described method, and FIG. 7 illustrates a case in which the decision and quantization unit 23 quantizes 3 bits, and FIG. 8 illustrates a case of quantizing 4 bits. The difference is shown. The curves denoted by * in Figs. 7 and 8 are conventional cases, and the curves denoted by ⅹ are cases of the present invention. That is, as can be seen in Figure 7 it can be seen that the present invention obtains a CNR gain of about 1dB at 2 * 10 ^-4 which is a standard of QAF (Quasi Error Free), compared to the conventional method. This means that the transmitter can demodulate sufficiently even if the data is transmitted with a power of about 1 dB. On the contrary, it means that the data can be demodulated even if the intensity of the received power is about 1 dB.

On the other hand, the present invention is applicable to all digital communication systems employing COFDM as well as digital TV. In addition, when the CSI value is known, the present invention can be used in both the single carrier method and the multicarrier method.

As described above, according to the demapping method and apparatus according to the present invention, in the case of demapping received data, the area is classified by appropriately distinguishing the input data so that the distance difference is reflected as it is, and not forcibly limited. Can be distinguished. In addition, reliability can be improved by performing soft decision and quantization in a predetermined interval by multiplying the region division value according to the above method with the channel state information.

When the channel state information value is too small, it is outputted as a constant value or forced soft decision, thereby preventing an error caused by the product of the area division value and the channel state information when the channel state information is very small. have.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing a conventional area classification method in 16-QAM.

2 is a block diagram illustrating a demapping apparatus according to the present invention.

3 is a graph illustrating a method of classifying data regions of the present invention corresponding to the first bit in each coordinate axis when the transmitter is mapped to 16-QAM.

4 is a graph illustrating a method of classifying data regions of the present invention corresponding to the second bit in each coordinate axis when the transmitter is mapped to 16-QAM.

FIG. 5 is a graph illustrating an example of a method of outputting channel state information of FIG. 2. FIG.

FIG. 6 is a graph illustrating a method of classifying data regions of the present invention corresponding to the third bit in each coordinate axis when the transmitter is mapped to 64-QAM. FIG.

FIG. 7 is a graph comparing the case of quantization with 3 bits after obtaining the region classification value and the channel state information value according to the present invention.

8 is a graph comparing the case of quantization with 4 bits after obtaining the region discrimination value and the channel state information value according to the present invention.

Explanation of symbols for main parts of the drawings

21: area detector 22: power calculator

23 decision and quantization unit 24 internal deinterleaver

25: Viterbi Decoder

Claims (14)

In the demapping method of mapping the transmission data to a predetermined constellation according to a modulation method and receiving the transmitted data and demapping in the reverse process of the mapping, Linearly dividing the area of the value with respect to the received real axis and the imaginary axis data to reflect the distance difference as it is; And multiplying the received channel state information by an area division value of the step to perform quantization. In the demapping apparatus for mapping the transmission data to a certain constellation according to a modulation method, receiving the transmitted data, passing through a fast Fourier transform (FFT), equalizer, and demapping in the reverse process of the mapping, A power calculation unit that receives the channel state information of each QAM symbol as an input, calculates and normalizes signal power, and outputs this value as the channel state information value; An area detection unit for linearly dividing an area of the value with respect to the real axis and the imaginary axis data output from the equalizer, and reflecting the distance difference as it is; And a decision and quantization unit configured to multiply the channel state information of the power calculation unit by the values divided by the respective areas in the area detection unit and to quantize the difference between the multiplied values. The method of claim 2, wherein the area detection unit The demapping apparatus according to claim 1, wherein the bit mapping of the real and imaginary axes outputted from the equalizer is not forcibly limited when the area is not within a predetermined mapping data range. The method of claim 2, wherein the decision and quantization unit And when the channel state information value is smaller than a preset threshold value, output one of the values equal to or greater than the threshold value as a channel state information value and multiply the area discrimination value. The method of claim 2, wherein the decision and quantization unit And if the channel state information is less than a preset threshold, forcibly soft-decides the region division value to a predetermined value. The method of claim 1, wherein the area classification step is performed. When the modulation scheme of the transmitting end is 16-QAM, the area-mapping value of the data corresponding to the first bit of the real and imaginary axis data received is output as -x when the input data is x. . The method of claim 1, wherein the area classification step is performed. When the modulation scheme of the transmitting end is 16-QAM, the area discrimination value of the data corresponding to the second bit of the real and imaginary axis data received is output as-| x | + 2 when the input data is x. Demapping method. The method of claim 1, wherein the area classification step is performed. When the modulation scheme of the transmitter is 64-QAM, the area-mapping value of the data corresponding to the first bit of the received real and imaginary axis data is output as -x when the input data is x. . The method of claim 1, wherein the area classification step is performed. When the modulation scheme of the transmitter is 64-QAM, the area discrimination value of the data corresponding to the second bit of the received real and imaginary axis data is output as-| x | + 4 when the input data is x. Demapping method. The method of claim 1, wherein the area classification step is performed. When the modulation scheme of the transmitter is 64-QAM, the area discrimination value of the data corresponding to the third bit of the real and imaginary axis data to be received is x when the input data is x and the value of x is less than | 4 |, Demapping method, characterized in that output as | x | -2. The method of claim 1, wherein the area classification step is performed. If the modulation scheme of the transmitting end is 64-QAM, the area discrimination value of the data corresponding to the third bit of the real and imaginary axis data to be received is -x if the input data is x and the value of x is greater than | 4 | A demapping method characterized by outputting x | +6. The method of claim 1, wherein the area classification step is performed. If the modulation scheme of the transmitter is QPSK and the -1,0 bit is mapped to -1,0 on the real and imaginary axes, the area-division value of the received real and imaginary axis data is- A demapping method characterized by outputting as x. The method of claim 1, wherein the quantization step And if the channel state information value is smaller than a preset threshold value, output one of the values above the threshold value as a channel state information value and multiply the area discrimination value. The method of claim 1, wherein the quantization step And if the channel state information is smaller than a preset threshold, forcibly soft-decides the region division value to a predetermined value.