KR20210133946A - Modulator using non-uniform 16-symbol signal constellation for low density parity check codeword with 2/15 code rate, and method using the same - Google Patents

Abstract

A modulator using a non-uniform 16-symbol signal constellation and a modulation method thereof are disclosed. According to an embodiment of the present invention, the modulator using a non-uniform 16-symbol signal constellation comprises: a memory for receiving a codeword corresponding to an LDPC code whose code rate is 2/15; and a processor that maps the codeword onto 16 symbols of a non-uniform 16-symbol signal constellation by a 4 bit unit.

Description

Modulator using non-uniform 16-symbol signal constellation for LDPC codeword with code rate of 2/15 and modulation method using same {MODULATOR USING NON-UNIFORM 16-SYMBOL SIGNAL CONSTELLATION FOR LOW DENSITY PARITY CHECK CODEWORD WITH 2/15 CODE RATE , AND METHOD USING THE SAME}

The present invention relates to symbol mapping using non-uniform signal constellation, and more particularly, to a modulator for transmitting error-correction-coded data in a digital broadcasting channel.

BICM (Bit-Interleaved Coded Modulation) is a bandwidth-efficient transmission technology that includes an error-correction coder, a bit-by-bit interleaver, and a high-order modulator. It is a combined form.

BICM can provide excellent performance with a simple structure by using a low-density parity check (LDPC) encoder or a turbo encoder as an error correction encoder. In addition, the BICM provides a high level of flexibility because a modulation order, a length of an error correction code, and a code rate can be variously selected. Because of these advantages, BICM is highly likely to be used not only in broadcasting standards such as DVB-T2 and DVB-NGH, but also in other next-generation broadcasting systems.

Despite these advantages, BICM is significantly different from the Shannon limit in terms of capacity. In order to reduce the difference with the Shannon limit, modulation using better signal properties is essential.

It is an object of the present invention to provide a modulator and a modulation method using a non-uniform signal constellation that is more efficient than a uniform signal constellation in order to transmit error-correction coded data in a broadcasting system channel.

Another object of the present invention is to provide a modulator and a modulation method for non-uniform 16-symbol mapping that is optimized for an LDPC encoder having a code rate of 2/15 and can be applied to a next-generation broadcasting system such as ATSC 3.0. .

A modulator using a non-uniform 16-symbol signal constellation according to the present invention for achieving the above object includes: a memory for receiving a codeword corresponding to an LDPC code having a code rate of 2/15; and a processor that maps the codeword to one of 16 symbols of a non-uniform 16-symbol signal constellation in units of 4 bits.

In this case, the distance between the 16 symbols is non-uniform, and the first group of 4 symbols in the first quadrant and the 4 symbols of the first group are symmetric with respect to the imaginary axis. a second group of 4 symbols, a third group of 4 symbols symmetric with respect to the origin with the 4 symbols of the first group, and a second group symmetric with respect to the real axis with the 4 symbols of the first group It can contain 4 groups.

In this case, a vector corresponding to the first group of four symbols w ₀ , w ₁ , w ₂ , and w ₃ is w, and the second group of four symbols w ₄ , w ₅ , w _The vector corresponding to 6 , w ₇ ) is -conj(w) (conj(w) is a function that outputs the complex conjugate of all elements of w), and 4 symbols of the third group (w ₁₂ , w _{13 )} , w ₁₄ , w ₁₅ ) may be -w, and the vector corresponding to the four symbols of the fourth group (w ₈ , w ₉ , w ₁₀ , w ₁₁ ) may be conj(w). .

In this case, two of the four symbols of the first group may have symmetrical amplitudes of real components and imaginary components.

In this case, the four symbols of the first group are w ₀ , w ₁ , w ₂ and w ₃ , and |real(w ₀ )| = |imaginary(w ₁ )|(real(i) is a function that outputs the real component of i, imaginary(i) is a function that outputs the imaginary component of i, i is an arbitrary complex number), |real(w ₁ )| = |imaginary(w ₀ )|, and |real(w ₂ )| = |imaginary(w ₃ )|, and |real(w ₃ )| = |imaginary(w ₂ )|

In this case, the 16 symbols may be defined as shown in the table below.

[graph]

In addition, a modulation method using a non-uniform 16-symbol signal constellation according to the present invention includes: receiving a codeword corresponding to an LDPC code having a code rate of 2/15; mapping the codeword to one of 16 symbols of a non-uniform 16-symbol signal constellation in 4-bit units; and adjusting at least one of an amplitude and a phase of a carrier wave according to the mapping.

In addition, the BICM apparatus according to the present invention includes an error correction encoder for outputting an LDPC codeword having a code rate of 2/15; a bit interleaver for outputting an interleaved codeword by interleaving the LDPC codeword in units of bit groups having a size corresponding to a parallel factor of the LDPC codeword; and a modulator that maps the interleaved codeword to 16 symbols of a non-uniform 16-symbol signal constellation in units of 4 bits.

According to the present invention, by intentionally distorting a signal constellation for transmitting error-correction coded data in a next-generation broadcasting system, significantly improved performance can be obtained compared to the uniform signal constellation.

In addition, the present invention provides a non-uniform 16-symbol signal constellation that is optimized for an LDPC encoder having a code rate of 2/15 and can be applied to a next-generation broadcasting system such as ATSC 3.0.

1 is a block diagram illustrating a broadcast signal transmission/reception system according to an embodiment of the present invention.
2 is an operation flowchart illustrating a broadcast signal transmission/reception method according to an embodiment of the present invention.
3 is a diagram illustrating a structure of a parity check matrix corresponding to an LDPC code according to an embodiment of the present invention.
4 is a diagram illustrating bit groups of an LDPC codeword having a length of 64800.
5 is a diagram illustrating bit groups of an LDPC codeword having a length of 16200.
6 is a diagram illustrating interleaving in units of bit groups according to an interleaving sequence.
7 is a diagram illustrating a signal constellation of 16-QAM.
8A and 8B are diagrams illustrating a non-uniform 16-symbol signal constellation optimized for an LDPC code having a code rate of 2/15.
9 is a diagram showing the performance of the uniform signal constellation shown in FIG. 7 and the non-uniform signal constellation shown in FIG. 8A for an LDPC code having a code rate of 2/15.
10 is a block diagram illustrating a modulator using a 16-symbol non-uniform signal constellation according to an embodiment of the present invention.
11 is an operation flowchart illustrating a modulation method using a 16-symbol non-uniform signal constellation according to an embodiment of the present invention.

The present invention will be described in detail with reference to the accompanying drawings as follows. Here, repeated descriptions, well-known functions that may unnecessarily obscure the gist of the present invention, and detailed descriptions of configurations will be omitted. Embodiments of the present invention are provided in order to more completely explain the present invention to those of ordinary skill in the art. Accordingly, the shapes and sizes of elements in the drawings may be exaggerated for clearer description.

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

1 is a block diagram illustrating a broadcast signal transmission/reception system according to an embodiment of the present invention.

Referring to FIG. 1 , it can be seen that the BICM device 10 and the BICM receiving device 30 communicate via the wireless channel 20 .

The BICM device 10 encodes k-bit information bits 11 in the error correction encoder 13 to generate an n-bit codeword. In this case, the error correction encoder 13 may be an LDPC encoder or a turbo encoder.

The codeword is interleaved by the bit interleaver 14 to generate an interleaved codeword.

In this case, interleaving may be performed in units of bit groups. In this case, the error correction encoder 13 may be an LDPC encoder having a length of 16200 and a code rate of 2/15, a codeword having a length of 16200 may be divided into a total of 45 bit groups, and each of the bit groups is an LDPC encoder. It may include 360 bits that are parallel factors of the codeword.

In this case, interleaving may be performed in units of bit groups corresponding to an interleaving sequence to be described later.

At this time, the bit interleaver 14 effectively disperses the clustering errors generated in the channel to prevent performance degradation of the error correction code. In this case, the bit interleaver 14 may be individually designed according to the length and code rate of the error correction code and the modulation order.

The interleaved codeword is modulated by the modulator 15 and transmitted through the antenna 17 .

In this case, the modulator 15 is a concept including a symbol mapping device. In this case, the modulator 15 may be a symbol mapping device that performs 16-symbol mapping in which codes are mapped to 16 constellations.

In this case, the modulator 15 may be a uniform modulator such as a Quadrature Amplitude Modulation (QAM) modulator, or a non-uniform modulator.

In particular, the modulator 15 may be a symbol mapping device that performs non-uniform constellation (NUC) symbol mapping having 16 constellations. That is, the modulator 15 may map the interleaved codeword to 16 symbols of a non-uniform 16-symbol signal constellation in units of 4 bits.

A signal transmitted through the radio channel 20 is received through the antenna 31 of the BICM receiving device 30 , and the BICM receiving device 30 undergoes a reverse process of the process that occurred in the BICM device 10 . That is, the received data may be demodulated by the demodulator 33 , deinterleaved by the bit deinterleaver 34 , and then decoded by the error correction decoder 35 to finally recover information bits.

It is apparent to those skilled in the art that, in addition to the above-described transmission/reception process being described within the minimum range necessary to describe the characteristics of the present invention, many processes necessary for data transmission may be added.

2 is an operation flowchart illustrating a broadcast signal transmission/reception method according to an embodiment of the present invention.

Referring to FIG. 2 , in the method for transmitting/receiving a broadcast signal according to an embodiment of the present invention, first, information bits are error-corrected and encoded ( S210 ).

That is, in step S210, k-bit information bits are encoded by an error correction encoder to generate an n-bit codeword.

In this case, step S210 may be performed like an LDPC encoding method to be described later.

In addition, in the broadcast signal transmission/reception method, an interleaved codeword is generated by interleaving an n-bit codeword in units of bit groups ( S220 ).

In this case, the n-bit codeword may be an LDPC codeword having a length of 16200 and a code rate of 2/15, and a codeword having a length of 16200 may be divided into a total of 45 bit groups, and each of the bit groups is an LDPC codeword. It may include 360 bits corresponding to a parallel factor of .

In this case, interleaving may be performed in units of bit groups corresponding to an interleaving sequence to be described later.

In addition, the broadcast signal transmission/reception method modulates the encoded data (S230).

That is, in step S230, the interleaved codeword is modulated by the modulator.

In this case, the modulator is a concept including a symbol mapping device. In this case, the modulator may be a symbol mapping device that performs 16-symbol mapping in which codes are mapped to 16 constellations.

In this case, the modulator may be a uniform modulator, such as a Quadrature Amplitude Modulation (QAM) modulator, or a non-uniform modulator.

In particular, the modulator may be a symbol mapping device that performs non-uniform constellation (NUC) symbol mapping having 16 constellations. That is, the modulator may map the interleaved codeword to 16 symbols of a non-uniform 16-symbol signal constellation in units of 4 bits.

In addition, the broadcast signal transmission/reception method transmits modulated data (S240).

That is, in step S240, the modulated codeword is transmitted to the radio channel through the antenna.

In addition, the broadcast signal transmission/reception method demodulates the received data (S250).

That is, in step S250, a signal transmitted through a radio channel is received through an antenna of a receiver, and the received data is demodulated by a demodulator.

Also, in the broadcast signal transmission/reception method, the demodulated data is deinterleaved ( S260 ). In this case, the deinterleaving of step S260 may correspond to the reverse process of step S220.

In addition, in the broadcast signal transmission/reception method, the deinterleaved codeword is error-corrected and decoded (S270).

That is, in step S270, error correction decoding is performed through an error correction decoder of the receiver to finally restore information bits.

In this case, step S270 may correspond to the reverse process of the LDPC encoding method, which will be described later.

The LDPC (Low Density Parity Check) code is known as a code close to the Shannon limit in the AWGN (Additive White Gaussian Noise) channel, and has asymptotically superior performance than the turbo code, parallel decoding, etc. has the advantage of

In general, the LDPC code is defined by a randomly generated low density PCM (parity check matrix). However, the randomly generated LDPC code not only requires a lot of memory to store the PCM, but also takes a lot of time to access the memory. To solve this problem, a quasi-cyclic LDPC (QC-LDPC) code has been proposed, and the QC-LDPC code composed of a zero matrix or CPM (Circulant Permutation Matrix) is expressed by It is defined by the PCM represented by 1.

[Equation 1]

Here, J is a CPM having a size of L x L and is given by Equation 2 below. Hereinafter, L may be 360.

[Equation 2]

In addition, J ⁱ is the L x L identity matrix I(=J ⁰ ) shifted to the right i(0=i<L) times, and J ^∞ is the L x L zero matrix. Accordingly, in the QC-LDPC code, ^{since only the exponent i needs} to be stored to store J i , the memory required to store the PCM is greatly reduced.

3 is a diagram illustrating a structure of a parity check matrix corresponding to an LDPC code according to an embodiment of the present invention.

Referring to FIG. 3 , the sizes of matrices A and C are g x K and (N-K-g) x (K+g), respectively, and are composed of a zero matrix having a size of L x L and a CPM. Also, matrix z is a zero matrix of size gx (NKg), matrix D is an identity matrix of size (NKg) x (NKg), and matrix B is a dual diagonal matrix of size gxg matrix). In this case, the matrix B may be a matrix in which all elements other than the diagonal element and the elements adjacent to the bottom of the diagonal are all 0, or may be defined as in Equation 3 below.

[Equation 3]

Here, I _LxL is an identity matrix of size L x L.

That is, the matrix B may be a bit-wise double diagonal matrix or a block-wise double diagonal matrix using the identity matrix as a block as expressed in Equation 3 above. A general (bit-wise) double diagonal matrix is disclosed in detail in Korean Patent Application Laid-Open No. 2007-0058438 or the like.

In particular, when the matrix B is a bit-wise double diagonal matrix, row permutation or column permutation is applied to the PCM of the structure shown in FIG. 3 including the matrix B. It is apparent to those skilled in the art that conversion to quasi-cyclic is possible.

In this case, N is the length of a codeword, and K is the length of information.

In the present invention, as shown in Table 1 below, a newly designed QC-LDPC code having a code rate of 2/15 and a codeword length of 16200 is proposed. That is, an LDPC code that receives information having a length of 2160 and generates an LDPC codeword having a length of 16200 is proposed.

Table 1 shows the sizes of the A, B, C, D, and Z matrices of the QC-LDPC code of the present invention.

The newly designed LDPC code may be expressed in the form of a sequence, an equivalent relationship is established between the sequence and the matrix (parity bit check matrix), and the sequence may be expressed as shown in the table below.

[table]

Line 1: 2889 3122 3208 4324 5968 7241 13215

Line 2: 281 923 1077 5252 6099 10309 11114

Line 3: 727 2413 2676 6151 6796 8945 12528

Line 4: 2252 2322 3093 3329 8443 12170 13748

Line 5: 575 2489 2944 6577 8772 11253 11657

Line 6: 310 1461 2482 4643 4780 6936 11970

Line 7: 8691 9746 10794 13582

Line 8: 3717 6535 12470 12752

Line 9: 6011 6547 7020 11746

Line 10: 5309 6481 10244 13824

Line 11: 5327 8773 8824 13343

Line 12: 3506 3575 9915 13609

Line 13: 3393 7089 11048 12816

Line 14: 3651 4902 6118 12048

Line 15: 4210 10132 13375 13377

LDPC codes expressed in sequence form are widely used in the DVB standard.

를 생성한다. 여기서, M₁=g, M₂=N-K-g이다. 또한, M₁은 이중 대각행렬(dual diagonal matrix) B에 대응하는 패러티(parity)의 크기이며, M₂는 항등행렬 D에 대응하는 패러티의 크기이다. 부호화 과정은 다음과 같다.According to an embodiment of the present invention, the LDPC code expressed in the form of a sequence is encoded as follows. Assume that an information block having an information size of K S=(s ₀ , s ₁ , ..., s _K-1 ). The LDPC encoder uses an information block S with a size of K to obtain a codeword _{with a size of N=K+M 1} +M ₂

create Here, M ₁ =g, M ₂ =NKg. Also, M ₁ is the size of parity corresponding to the dual diagonal matrix B, and M ₂ is the size of the parity corresponding to the identity matrix D. The encoding process is as follows.

-Initialization:

[Equation 4]

를 상기 테이블의 수열의 제1행에 명시된 패러티 비트 주소들(parity bit addresses)에서 누적(accumulate)한다. 예를 들어, 길이가 16200이며, 부호율이 2/15인 LDPC 부호에서의 누적 과정은 다음과 같다.-First

is accumulated from the parity bit addresses specified in the first row of the numerical sequence of the table. For example, an accumulation process in an LDPC code having a length of 16200 and a code rate of 2/15 is as follows.

)은 GF(2)에서 일어난다.Add here (

) occurs in GF(2).

들에 대해서는, 하기 수학식 5에서 계산된 패러티 비트 주소들에서 누적한다.-Next L-1 information bits, that is,

, are accumulated at the parity bit addresses calculated in Equation 5 below.

[Equation 5]

에 대응되는 패러티 비트 주소들, 즉 상기 테이블의 수열의 제1행에 표기된 패러티 비트 주소들을 나타내며, Q₁ = M₁/L, Q₂ = M₂/L, L = 360이다. 또한, Q₁과 Q₂는 하기 표 2에 정의된다. 예를 들어, 길이가 16200이며, 부호율이 2/15인 LDPC 부호는 M₁ = 3240, Q₁ = 9, M₂ = 10800, Q₂ = 30, L = 360이므로, 두 번째 비트

에 대해서는 상기 수학식 5를 이용하면 다음과 같은 연산이 수행된다.where x is the first bit

Parity bit addresses corresponding to , ie, parity bit addresses indicated in the first row of the sequence of the table, are Q ₁ = M ₁ /L, Q ₂ = M ₂ /L, and L = 360. In addition, Q ₁ and Q ₂ are defined in Table 2 below. For example, an LDPC code with a length of 16200 and a code rate of 2/15 is M ₁ = 3240, Q ₁ = 9, M ₂ = 10800, Q ₂ = 30, L = 360, so the second bit

With respect to Equation 5 above, the following operation is performed.

Table 2 shows the sizes _{of M 1} , M ₂ , Q ₁ , and Q ₂ of the designed QC-LDPC code.

부터

까지의 새로운 360개의 정보비트들은 상기 수열의 제2행을 이용하여, 상기 수학식 5로부터 패러티 비트 누적기들의 주소를 계산하고, 누적한다.-the next

from

For the new 360 information bits up to, the addresses of the parity bit accumulators are calculated from Equation (5) and accumulated using the second row of the sequence.

- In a similar way, for all groups composed of the new L information bits, the addresses of the parity bit accumulators are calculated and accumulated from Equation 5 using the new row of the sequence.

에서

까지의 모든 정보비트들이 사용된 후, i = 1부터 시작하여 하기 수학식 6의 연산을 순차적으로 수행한다.-

at

After all information bits up to , are used, the operation of Equation 6 below is sequentially performed starting from i = 1.

[Equation 6]

- Next, when parity interleaving is performed as in Equation 7 below, parity generation corresponding to the double diagonal matrix B is completed.

[Equation 7]

)를 이용하여 이중 대각행렬 B에 대응하는 패러티 생성이 완료되면, M₁개의 생성된 패러티(

)을 이용하여, 항등행렬 D에 대응하는 패러티를 생성한다.K information bits (

), when the parity generation corresponding to the double diagonal matrix B is completed, M ₁ generated parity (

) to generate a parity corresponding to the identity matrix D.

에서

까지의 L개의 비트들로 구성된 모든 그룹(group)들에 대해서, 상기 수열들의 새로운 행(이중 대각행렬 B에 대응하는 패러티를 생성할 때 이용한 마지막 행의 바로 다음 행부터 시작)과 상기 수학식 5를 이용하여 패러티 비트 누적기들의 주소를 계산하고, 관련 연산을 수행한다.-

at

For all groups consisting of L bits up to, a new row of the sequence (starting from the row immediately following the last row used to generate the parity corresponding to the double diagonal matrix B) and Equation 5 Calculate the addresses of parity bit accumulators using , and perform related operations.

에서

까지의 모든 비트들이 사용된 후, 하기 수학식 8과 같은 패러티 인터리빙을 수행하면, 항등행렬 D에 대응하는 패러티 생성이 완료된다.-

at

After all the bits up to , are used, parity interleaving is performed as in Equation 8 below, and parity generation corresponding to the identity matrix D is completed.

[Equation 8]

4 is a diagram illustrating bit groups of an LDPC codeword having a length of 64800.

Referring to FIG. 4 , it can be seen that an LDPC codeword having a length of 64800 ^{is divided into 180 bit groups (0 th} group to 179 ^{th group).}

In this case, 360 may be a parallel factor (PF) of the LDPC codeword. That is, since PF is 360, an LDPC codeword having a length of 64800 is divided into 180 bit groups as shown in FIG. 4, and each bit group includes 360 bits.

5 is a diagram illustrating bit groups of an LDPC codeword having a length of 16200.

Referring to FIG. 5 , it can be seen that an LDPC codeword having a length of 16200 ^{is divided into 45 bit groups (0 th} group to 44 ^{th group).}

In this case, 360 may be a parallel factor (PF) of the LDPC codeword. That is, since PF is 360, an LDPC codeword having a length of 16200 is divided into 45 bit groups as shown in FIG. 5, and each bit group includes 360 bits.

6 is a diagram illustrating interleaving in units of bit groups according to an interleaving sequence.

Referring to FIG. 6 , it can be seen that interleaving is performed by changing the order of bit groups according to the designed interleaving sequence.

For example, it is assumed that the interleaving sequence for an LDPC codeword having a length of 16200 is as follows.

Interleaving sequence = {24 34 15 11 2 28 17 25 5 38 19 13 6 39 1 14 33 37 29 12 42 31 30 32 36 40 26 35 44 4 16 8 20 43 21 7 0 18 23 3 10 41 9 27 22}

Then, the order of bit groups of the LDPC codeword as shown in FIG. 4 is changed as shown in FIG. 6 by the interleaving sequence.

That is, the LDPC codeword 610 and the interleaved codeword 620 each include 45 bit groups, and the LDPC codeword 620 in which the 24th bit group of the LDPC codeword 610 is interleaved by an interleaving sequence. is the 0th bit group, the 34th bit group of the LDPC codeword 610 becomes the 1st bit group of the interleaved LDPC codeword 620, and the 15th bit group of the LDPC codeword 610 is interleaved. The second bit group of the LDPC codeword 620 becomes the 11th bit group of the LDPC codeword 610 becomes the third bit group of the interleaved LDPC codeword 620, and the 2nd bit group of the LDPC codeword 610 is It can be seen that the th bit group becomes the 4 th bit group of the interleaved LDPC codeword 620 .

는 N _group = N _ldpc / 360 개의 비트그룹들로 쪼개어진다. 이 때, N _ldpc 는 16200일 수 있다.LDPC codeword of length N _ldpc

is divided into N _group = N _ldpc / 360 bit groups. In this case, N _ldpc may be 16200.

[Equation 9]

Here, X _j represents the j-th bit group, and each X _j is composed of 360 bits.

The LDPC codewords divided into bit groups are interleaved as shown in Equation 10 below.

[Equation 10]

Here, Y _j represents an interleaved j-th bit group, and π( j ) is a permutation order for interleaving per bit group. The permutation order corresponds to the interleaving sequence of Equation 11 below.

[Equation 11]

interleaved sequence

={5 33 18 8 29 10 21 14 30 26 11 23 27 4 7 6 24 44 38 31 34 43 13 0 15 42 17 2 20 12 40 39 35 32 1 3 41 37 9 25 19 22 16 28 36}

That is, assuming that each of the codeword and the interleaved codeword includes 45 bitgroups from the 0th bitgroup to the 44th bitgroup, the interleaving sequence of Equation 11 is a codeword in which the 5th bitgroup of the codeword is interleaved. is the 0th bit group, the 33rd bit group of the codeword becomes the 1st bit group of the interleaved codeword, the 18th bit group of the codeword becomes the 2nd bit group of the interleaved codeword, and the codeword The 8th bit group of , becomes the 3rd bit group of the interleaved codeword, ..., the 28th bit group of the codeword becomes the 43rd bit group of the interleaved codeword, and the 36th bit group of the codeword becomes the This means that it becomes the 44th bit group of the interleaved codeword.

In particular, the interleaving sequence shown in Equation 11 is optimized when 16-symbol mapping (in particular, NUC symbol mapping) is used and an LDPC encoder having a length of 16200 and a code rate of 2/15 is used.

In general, uniform quadrature amplitude modulation (QAM) is used to transmit error-correction coded data in a broadcasting and communication system.

7 is a diagram illustrating a signal constellation of 16-QAM.

Referring to FIG. 7 , it can be seen that 16 symbols of a signal constellation of 16-QAM to which 4 bits are mapped are uniformly distributed.

In FIG. 7 , gray mapping is applied to the bit string mapping between symbols, but other types of bit string mapping may also be used.

In the equivalent 16-QAM illustrated in FIG. 7 , the distance between constellation points is constant. Although the uniform QAM has an advantage that it can be used regardless of the code rate of the error correction code, it has to show lower performance compared to the non-uniform signal characteristics specialized for a specific code rate. Theoretically, in an AWGN (Addictive White Gaussian Noise) channel environment, when the amplitude of the channel input signal (transmission signal) and the amplitude of the channel itself follow a Gaussian distribution at the same time, between the transmission signal and the reception signal It is known that the capacity (capacity), which is mutual information of , becomes the maximum. Based on this theoretical background, better performance can be obtained compared to the uniformity constellation through intentional distortion of the signal constellation.

A symmetrical design technique may be used to design the non-uniform signal constellation.

That is, in the case of 16-QAM, four signal constellation symbols in the first quadrant are preferentially designed, and then the signal constellation symbols for the remaining three quadrants can be symmetrically designed.

For example, if a vector of four signal constellation symbols in the first quadrant is w=(w ₀ , w ₁ , w ₂ , w ₃ ), a vector of signal constellation symbols for the remaining quadrant may be determined as follows.

- Quadrant 1 : (w ₀ , w ₁ , w ₂ , w ₃ ) = w

- Quadrant 2 : (w ₄ , w ₅ , w ₆ , w ₇ ) = -conj(w)

- Quadrant 3 : (w ₁₂ , w ₁₃ , w ₁₄ , w ₁₅ ) = -w

- Quadrant 4 : (w ₈ , w ₉ , w ₁₀ , w ₁₁ ) = conj(w)

Here, conj(w) may be a function that outputs the complex conjugate of all elements of w.

Of course, the vector of signal constellation symbols may be determined in various other ways.

The symbol w _i may have a bit string mapping value corresponding to a decimal value i. For example, w ₃ = 3 ₍₁₀₎ = 0010 ₍₂₎ .

When designing a non-uniform signal constellation, using a symmetric design technique has an advantage in that complexity can be greatly reduced.

In order to further reduce design complexity, it may be assumed that real and imaginary amplitudes of vectors w corresponding to four signal constellation symbols in the first quadrant are symmetric. That is, two of the four symbols in the first quadrant may have symmetric amplitudes of real components and imaginary components.

In this case, instead of designing four complex numbers, four PAM (Pulse Amplitude Modulation) points are designed. In this case, the smallest PAM value may be set to 1, and the power may be normalized after finding the remaining three PAM values. As a result, by using the above-mentioned symmetry, if three PAM values are designed, a total of 16 signal constellations can be generated.

In general, in ^{order to design L = M 2} signal constellations, M-1 PAM values may be designed.

When M-1 PAM values are obtained, a result of power normalization of the obtained M-1 PAM values and the smallest PAM value is defined as PAM_norm = [P ₁ P ₂ ... P _{M ].} In calculating w using PAM_norm, using the assumption that the PAM values of real and imaginary are symmetric, it can be expressed as follows.

|real(w ₀ )| = |imaginary(w ₁ )|

|real(w ₁ )| = |imaginary(w ₀ )|

|real(w ₂ )| = |imaginary(w ₃ )|

|real(w ₃ )| = |imaginary(w ₂ )|

(real(i) is a function that outputs the real component of i, imaginary(i) is a function that outputs the imaginary component of i, and i is an arbitrary complex number)

That is, if a real value of a vector w corresponding to the symbols in the first quadrant is defined, all imaginary values of w are defined accordingly. In the case of 16-QAM having a total of 4 symbols in the first quadrant, 4! (factorial) = 4 X 3 X 2 X 1 = 24 combination methods as shown in Table 3 below. Table 3 below shows 24 methods for obtaining w, which is a vector corresponding to the symbols in the first quadrant.

Way _{Real of} w 0 _{Imaginary of} w 0 _{Real of} w 1 _{Imaginary of} w 1 _{Real in w2 Imaginary of} w 2 _{Real of} w 3 _{Imaginary of} w 3 One P ₁ P ₂ P ₂ P ₁ P ₃ P ₄ P ₄ P ₃ 2 P ₁ P ₂ P ₂ P ₁ P ₄ P ₃ P ₃ P ₄ 3 P ₁ P ₃ P ₃ P ₁ P ₂ P ₄ P ₄ P ₂ 4 P ₁ P ₃ P ₃ P ₁ P ₄ P ₂ P ₂ P ₄ 5 P ₁ P ₄ P ₄ P ₁ P ₂ P ₃ P ₃ P ₂ 6 P ₁ P ₄ P ₄ P ₁ P ₃ P ₂ P ₂ P ₃ 7 P ₂ P ₁ P ₁ P ₂ P ₃ P ₄ P ₄ P ₃ 8 P ₂ P ₁ P ₁ P ₂ P ₄ P ₃ P ₃ P ₄ 9 P ₂ P ₃ P ₃ P ₂ P ₁ P ₄ P ₄ P ₁ 10 P ₂ P ₃ P ₃ P ₂ P ₄ P ₁ P ₁ P ₄ 11 P ₂ P ₄ P ₄ P ₂ P ₁ P ₃ P ₃ P ₁ 12 P ₂ P ₄ P ₄ P ₂ P ₃ P ₁ P ₁ P ₃ 13 P ₃ P ₁ P ₁ P ₃ P ₂ P ₄ P ₄ P ₂ 14 P ₃ P ₁ P ₁ P ₃ P ₄ P ₂ P ₂ P ₄ 15 P ₃ P ₂ P ₂ P ₃ P ₁ P ₄ P ₄ P ₁ 16 P ₃ P ₂ P ₂ P ₃ P ₄ P ₁ P ₁ P ₄ 17 P ₃ P ₄ P ₄ P ₃ P ₁ P ₂ P ₂ P ₁ 18 P ₃ P ₄ P ₄ P ₃ P ₂ P ₁ P ₁ P ₂ 19 P ₄ P ₁ P ₁ P ₄ P ₂ P ₃ P ₃ P ₂ 20 P ₄ P ₁ P ₁ P ₄ P ₃ P ₂ P ₂ P ₃ 21 P ₄ P ₂ P ₂ P ₄ P ₁ P ₃ P ₃ P ₁ 22 P ₄ P ₂ P ₂ P ₄ P ₃ P ₁ P ₁ P ₃ 23 P ₄ P ₃ P ₃ P ₄ P ₁ P ₂ P ₂ P ₁ 24 P ₄ P ₃ P ₃ P ₄ P ₂ P ₁ P ₁ P ₂

For example, an optimal PAM_norm value designed for an LDPC code having a code rate of 2/15 may be [0.7062 0.7075 0.7072 0.7077]. In this case, the obtained PAM_norm is used as the first quadrant symbol using method 1 of Table 3 above. Converting to the vector w corresponding to , we get w = [0.7062 + 0.7075i 0.7075 + 0.7062i 0.7072 + 0.7077i 0.7077 + 0.7072i].

Table 4 below shows 16 symbols of a non-uniform 16-symbol signal constellation optimized for an LDPC code having a code rate of 2/15. In general, since the error correction code has different operating SNR and error correction capability depending on the code rate, the performance of the BICM can be maximized by using the vector w value optimized for each code rate. If a non-uniform signal constellation optimized for a specific code rate is used for a different code rate, the performance of the BICM may be greatly reduced, so it is important to use an unequal signal constellation suitable for the code rate of the LDPC code.

w Constellation 0 0.7062 + 0.7075i One 0.7075 + 0.7062i 2 0.7072 + 0.7077i 3 0.7077 + 0.7072i 4 -0.7062 + 0.7075i 5 -0.7075 + 0.7062i 6 -0.7072 + 0.7077i 7 -0.7077 + 0.7072i 8 0.7062 - 0.7075i 9 0.7075 - 0.7062i 10 0.7072 - 0.7077i 11 0.7077 - 0.7072i 12 -0.7062 - 0.7075i 13 -0.7075 - 0.7062i 14 -0.7072 - 0.7077i 15 -0.7077 - 0.7072i

8A and 8B are diagrams illustrating a non-uniform 16-symbol signal constellation optimized for an LDPC code having a code rate of 2/15. Referring to FIGS. 8A and 8B, 16-symbols to which 4 bits are mapped. It can be seen that the 16 symbols of the non-uniform signal constellation are non-uniformly distributed. In the case of FIG. 8A , four symbols are too clustered in each quadrant, so it looks like one symbol, but when enlarged, it is as shown in FIG. 8B .

8A and 8B show a non-uniform 16-symbol signal constellation calculated based on the designed w. In this case, the bit stream of each symbol shown in FIGS. 8A and 8B is expressed based on gray mapping, but other types of bit string mapping are also applicable.

In particular, although FIG. 8B shows only the case of the first quadrant, it has already been described that the positions of the symbols in the other quadrants can be obtained from the positions of the symbols in the first quadrant.

9 is a diagram illustrating the performance of the uniform signal constellation shown in FIG. 7 and the non-uniform signal constellation shown in FIGS. 8A and 8B for an LDPC code having a code rate of 2/15.

Referring to FIG. 9 , it can be seen that BER (Bit Error Rate) and FER (Frame Error Rate) of unequal signal constellation and equivalent 16-QAM according to the present invention are shown. In FIG. 9 , the non-uniform signal constellation shows superior performance compared to the equivalent 16-QAM.

10 is a block diagram illustrating a modulator using a 16-symbol non-uniform signal constellation according to an embodiment of the present invention.

Referring to FIG. 10 , a modulator using a 16-symbol non-uniform signal constellation according to an embodiment of the present invention includes memories 1010 and 1030 and a processor 1020 . In this case, the modulator shown in FIG. 10 may correspond to the modulator 15 shown in FIG. 1 .

The memory 1010 receives a codeword corresponding to an LDPC code having a code rate of 2/15.

In this case, the codeword may be an error correction coded LDPC codeword or an interleaved LDPC codeword.

The processor 1020 maps the codeword to 16 symbols of a non-uniform 16-symbol signal constellation in units of 4 bits.

In this case, the processor 1020 may adjust any one or more of an amplitude and a phase of a carrier in accordance with the symbol mapping.

At this time, the 16 symbols have a non-uniform distance between the symbols, and the first group of 4 symbols in the first quadrant and the 4 symbols of the first group are symmetric with respect to the imaginary axis. A second group of four symbols, a third group of four symbols symmetric about the origin with the four symbols of the first group, and a fourth group symmetric with the four symbols of the first group about a real axis It can contain groups.

In this case, a vector corresponding to the first group of four symbols w ₀ , w ₁ , w ₂ , and w ₃ is w, and the second group of four symbols w ₄ , w ₅ , w _The vector corresponding to 6 , w ₇ ) is -conj(w) (conj(w) is a function that outputs the complex conjugate of all elements of w), and 4 symbols of the third group (w ₁₂ , w _{13 )} , w ₁₄ , w ₁₅ ) may be -w, and the vector corresponding to the four symbols of the fourth group (w ₈ , w ₉ , w ₁₀ , w ₁₁ ) may be conj(w). .

In this case, two of the four symbols of the first group may have symmetrical amplitudes of real components and imaginary components.

In this case, the four symbols of the first group are w ₀ , w ₁ , w ₂ and w ₃ , and |real(w ₀ )| = |imaginary(w ₁ )|(real(i) is a function that outputs the real component of i, imaginary(i) is a function that outputs the imaginary component of i, i is an arbitrary complex number), |real(w ₁ )| = |imaginary(w ₀ )|, and |real(w ₂ )| = |imaginary(w ₃ )|, and |real(w ₃ )| = |imaginary(w ₂ )|

In this case, the 16 symbols may be defined as shown in Table 4.

The memory 1030 may store additional information required for the operation of the processor 1020 . For example, the memory 1030 may store carrier frequency, amplitude, and the like.

The memory 1010 and the memory 1030 may correspond to various hardware for storing a set of bits, and data structures such as an array, a list, a stack, and a queue ( data structure).

In this case, the memory 1010 and the memory 1030 are not physically separate devices, but may physically correspond to different addresses of one device. That is, the memory 1010 and the memory 1030 are not physically separated, but may be separated only logically.

11 is an operation flowchart illustrating a modulation method using a 16-symbol non-uniform signal constellation according to an embodiment of the present invention.

Referring to FIG. 11, in the modulation method using a 16-symbol non-uniform signal constellation according to an embodiment of the present invention, a codeword corresponding to an LDPC code having a code rate of 2/15 is first generated. Receive (S1110).

In this case, the codeword may be an error correction coded LDPC codeword or an interleaved LDPC codeword. That is, in step S1110, the codeword may be directly received from the LDPC encoder, or the codeword may be received through a bit interleaver in the middle.

In addition, the modulation method using the 16-symbol non-uniform signal constellation according to an embodiment of the present invention maps the codeword to 16 symbols of the non-uniform 16-symbol signal constellation in units of 4 bits (S1120).

At this time, the 16 symbols have a non-uniform distance between the symbols, and the first group of 4 symbols in the first quadrant and the 4 symbols of the first group are symmetric with respect to the imaginary axis. A second group of four symbols, a third group of four symbols symmetric about the origin with the four symbols of the first group, and a fourth group symmetric with the four symbols of the first group about a real axis It can contain groups.

In this case, a vector corresponding to the first group of four symbols w ₀ , w ₁ , w ₂ , and w ₃ is w, and the second group of four symbols w ₄ , w ₅ , w _The vector corresponding to 6 , w ₇ ) is -conj(w) (conj(w) is a function that outputs the complex conjugate of all elements of w), and 4 symbols of the third group (w ₁₂ , w _{13 )} , w ₁₄ , w ₁₅ ) may be -w, and the vector corresponding to the four symbols of the fourth group (w ₈ , w ₉ , w ₁₀ , w ₁₁ ) may be conj(w). .

In this case, two of the four symbols of the first group may have symmetrical amplitudes of real components and imaginary components.

In this case, the four symbols of the first group are w ₀ , w ₁ , w ₂ and w ₃ , and |real(w ₀ )| = |imaginary(w ₁ )|(real(i) is a function that outputs the real component of i, imaginary(i) is a function that outputs the imaginary component of i, i is an arbitrary complex number), |real(w ₁ )| = |imaginary(w ₀ )|, and |real(w ₂ )| = |imaginary(w ₃ )|, and |real(w ₃ )| = |imaginary(w ₂ )|

In this case, the 16 symbols may be defined as shown in Table 4.

Also, in the modulation method using a 16-symbol non-uniform signal constellation according to an embodiment of the present invention, any one or more of an amplitude and a phase of a carrier is adjusted according to the mapping ( S1130 ).

The error correction encoder 13 shown in FIG. 1 may be implemented in the same structure as in FIG. 10 .

That is, the error correction encoder may include memories and a processor. In this case, the first memory may be a memory for storing an LDPC codeword having a length of 16200 and a code rate of 2/15, and the second memory may be a memory initialized to 0.

The memories may correspond to λ _i (i=0, 1, ..., N-1) and P _j (j=0, 1, ..., M ₁ +M ₂ -1), respectively.

The processor may generate the LDPC codeword corresponding to information bits by performing accumulation on the memory using a sequence corresponding to a parity check matrix.

In this case, the accumulation may be performed on parity bit addresses updated using a sequence of the table.

In this case, the LDPC codeword corresponds to the information bits and is a systematic part (λ ₀ , λ ₁ , ..., λ _K-1 ) having a length of 2160 (=K), included in the parity check matrix. The first parity part (λ _K , λ _K+1 , ..., λ _K+M1-1 ) corresponding to the double diagonal matrix and having a length of 3240 (=M ₁ =g) and the identity included in the parity check matrix It may include a second parity part (λ _K+M1 , λ _K+M1+1 , ..., λ _K+M1+M2-1 ) corresponding to the matrix and having a length of 10800 (=M _{2 ).}

At this time, the sequence is a value obtained by dividing 2160, which is the length of the systematic part, by 360, which is the CPM size (L) corresponding to the parity check matrix, and 3240, which is _{the length (M 1 ) of the first parity part, divided by 360.} It may have as many rows as the sum (2160/360+3240/360=15).

As described above, the sequence may be represented by the table.

In this case, the second memory may have a size corresponding to the sum (M ₁ +M _{2 ) of the length (M 1} ) of the first parity part and the length (M _{2 ) of the second parity part.}

In this case, the parity bit addresses may be updated based on a result of comparing each of the previous parity bit addresses (x) and the length (M _{1 ) of the first parity part indicated in each row of the sequence.}

That is, the parity bit addresses may be updated according to Equation 5 above. In this case, x is the previous parity bit address, m is an information bit index, an integer greater than 0 and smaller than L, L is the CPM size of the parity check matrix, Q ₁ is M ₁ /L, M ₁ is the first parity part The size of Q ₂ may be M ₂ /L, and M ₂ may be the size of the second parity part.

In this case, as described above, the accumulation may be performed while changing the rows of the sequence in units of the CPM size L=360 of the parity check matrix.

In this case, the first parity parts λ _K , λ _K+1 , ..., λ _K+M1-1 are parity interleaving using the first memory and the second memory, as described in Equation 7 above. (parity interleaving) may be performed.

In this case, the second parity part (λ _K+M1 , λ _K+M1+1 , ..., λ _K+M1+M2-1 ) is the first parity part (λ _{K ) as described through Equation (8).} , λ _K+1 , ..., λ _K+M1-1 ) After generation of the first parity part (λ _K , λ _K+1 , ..., λ _K+M1-1 ) and the sequence After the accumulation performed by using , parity interleaving using the first memory and the second memory is completed.

The bit interleaver 14 shown in FIG. 1 may also be implemented in the same structure as in FIG. 10 .

That is, the first memory may store an LDPC codeword having a length of 16200 and a code rate of 2/15. The processor may generate an interleaved codeword by interleaving the LDPC codeword in units of bit groups corresponding to a parallel factor of the LDPC codeword. In this case, the parallel factor may be 360. In this case, the bit group may include 360 bits. In this case, the LDPC codeword can be divided into 45 bit groups as shown in Equation 9 above.

In this case, interleaving may be performed using Equation (10) using a permutation order.

In this case, the permutation order may correspond to the interleaving sequence expressed by Equation (11).

The second memory provides the interleaved codeword as a modulator for 16-symbol mapping.

In this case, the modulator may be a symbol mapping apparatus that performs Non-Uniform Constellation (NUC) symbol mapping as described with reference to FIG. 10 .

As described above, in the modulator, modulation method, and BICM apparatus using a non-uniform 16-symbol signal constellation according to the present invention, the configuration and method of the embodiments described above are not limitedly applicable, but the embodiments are All or part of each of the embodiments may be selectively combined and configured so that various modifications may be made.

1010, 1030: memory
1020: Processor

Claims (7)

receiving a codeword corresponding to an LDPC code having a code rate of 2/15;
mapping the codeword to 16 symbols of a non-uniform 16-symbol signal constellation in units of 4 bits; and
and adjusting at least one of an amplitude and a phase of a carrier wave according to the mapping. The method according to claim 1,
The 16 symbols have a non-uniform distance between the symbols, and a first group of 4 symbols in the first quadrant, 4 symbols of the first group and 4 symbols symmetric with respect to the imaginary axis A second group of symbols, a third group of 4 symbols of the first group and a third group of 4 symbols symmetric with respect to the origin, and a fourth group of 4 symbols of the first group and a fourth group symmetric with respect to the real axis A modulation method using a non-uniform 16-symbol signal constellation, comprising: 3. The method according to claim 2,
A vector corresponding to the first group of 4 symbols w ₀ , w ₁ , w ₂ , w ₃ is w, and the second group of 4 symbols w ₄ , w ₅ , w ₆ , w _The vector corresponding to 7 ) is -conj(w) (conj(w) is a function that outputs the complex conjugate of all elements of w), and 4 symbols of the third group (w ₁₂ , w ₁₃ , w _{14 )} , w ₁₅ ) is a vector corresponding to -w, and the vector corresponding to the four symbols of the fourth group (w ₈ , w ₉ , w ₁₀ , w ₁₁ ) is conj(w). Modulation method using uniform 16-symbol signal constellation. 4. The method according to claim 3,
A modulation method using a non-uniform 16-symbol signal constellation, characterized in that two of the four symbols of the first group have symmetrical amplitudes of real components and imaginary components. 5. The method according to claim 4,
The four symbols of the first group are w ₀ , w ₁ , w ₂ and w ₃ , and |real(w ₀ )| = |imaginary(w ₁ )|(real(i) is a function that outputs the real component of i, imaginary(i) is a function that outputs the imaginary component of i, i is an arbitrary complex number), |real(w ₁ )| = |imaginary(w ₀ )|, and |real(w ₂ )| = |imaginary(w ₃ )|, and |real(w ₃ )| = |imaginary(w ₂ )| A modulation method using a non-uniform 16-symbol signal constellation, characterized in that. The method according to claim 1,
The 16 symbols are a modulation method using a non-uniform 16-symbol signal constellation, characterized in that defined as shown in the table below.
[graph]

an error correction encoder that outputs an LDPC codeword having a code rate of 2/15;
a bit interleaver for outputting an interleaved codeword by interleaving an input corresponding to the LDPC codeword in units of bit groups having a size corresponding to a parallel factor of the LDPC codeword; and
a modulator that maps an input corresponding to the interleaved codeword to 16 symbols of a non-uniform 16-symbol signal constellation in units of 4 bits;
The 16 symbols are a bit-interleaved coded modulation (BICM) device defined as shown in the table below.
[graph]

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