JP2002009861A - Encoding modulation/demodulation method for realizing variable transmission speed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an encoding modulation/demodulation method for realizing variable transmission speed by which reduction of a bit error rate is enabled without lowering power efficiency by block encoding which does not use a complicated means such as demodulator switching or an index signal in the collective transmission of frames different in transmission speed. SOLUTION: A block encoding modulation system where signal points different in the number of bits are arranged on the same signal space diagram face is constituted on the same channel and the signal points are properly selected. Thus, variable speed transmission is realized. In such a case, although an Euclidean distance between the signal points is reduced by the increase of the signal points resulting in possible deterioration in transmission characteristic, it is avoided by using the block encoding modulation system. Then, the error of the number of the transmission bits of a symbol is prevented by a method for encoding transmission bit information and incorporating it in a transmission code and a method for using set division.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coded modulation / demodulation method with a variable transmission rate, which can be used in technical fields such as channel coding and digital modulation, such as block coded modulation in digital communication. .
In particular, the present invention provides a method of simply transmitting and receiving a sequence having various transmission speeds in digital communication at once, and a method of realizing the method by one-way communication.

[0002]

2. Description of the Related Art A first prior art is shown in FIG. FIG.
1 shows a conventional method for realizing variable speed transmission in one direction, and has a feature that one type of modulation is used in the modulation method and is adapted to the fastest transmission method in the system. To change the transmission speed, a preamble is used as shown below. Information such as the number of transmission bits and the transmission speed is written in the preamble, and the receiving side decodes the preamble and decodes the required number of bits. Dummy data is inserted into portions other than the necessary bits. Thereby, variable transmission speed is realized. However, this method has a drawback that the power efficiency is reduced due to the insertion of dummy data and the fixed modulation scheme being the fastest transmission scheme. In addition, the receiving side has a disadvantage that a mechanism for decoding the preamble and selecting received data is required.

FIG. 20 shows a second conventional technique. FIG.
Shows another method for realizing variable speed transmission in one direction. In this method, index information is inserted into a transmission frame, information such as a modulation method is added, and a demodulator having a different method is selected and decoded on the receiving side based on the index signal. According to this method, it is possible to realize one-way variable speed transmission without lowering the power efficiency as in the first prior art. However, this method has a disadvantage that the transmission efficiency is reduced due to the insertion of the index signal. Further, the receiving side requires an index signal decoding mechanism and a plurality of demodulators, so that the structure is complicated.

FIG. 21 shows a third conventional technique. FIG.
Is an example of a method for implementing one-way speed variable transmission by devising a signal point arrangement. In the case of FIG. 21, 16QA
M (quadrature amplitude modulation) signal point and QPSK (quadrature phase modulation)
By simultaneously using signal points and setting transmission symbols to 16QAM points or QPSK points, transmission of sequences with different numbers of bits is realized. However, in this method, the shortest distance (d1) between the 16QAM signal point and the QPSK signal point is smaller than the shortest distance (d2) between the QPSK signal points because the Euclidean distance between adjacent signal points is 16QA.
There is a disadvantage that the bit error rate in the case of transmission of the signal point of M is greatly deteriorated as compared with the case of transmission of the signal point of QPSK, and the bit error rate becomes non-uniform and impractical.

[0005]

The conventional transmission method with a variable transmission rate has a drawback that power efficiency is reduced, and that a receiving side needs a mechanism for decoding a preamble and selecting received data. There were drawbacks. Further, the other method has a drawback that the transmission efficiency is reduced by inserting the index signal. Further, the receiving side requires a decoding mechanism for the index signal and a plurality of demodulators, so that the structure is complicated. In still another method, the bit error rate in the case of transmitting a signal point of 16QAM is significantly deteriorated as compared with the case of transmitting a signal point of QPSK, resulting in a non-uniform bit error rate, which is impractical. There was a disadvantage.

[0006] The present invention has been proposed in view of the above,
In batch transmission of frames with different transmission speeds in various applications, variable speed transmission can be realized without using complicated means such as demodulator switching, and power efficiency is reduced by block coding without using index signals etc. It is an object of the present invention to provide a coded modulation / demodulation method with a variable transmission rate, which can reduce the bit error rate without using any method.

[0007]

In order to achieve the above object, the present invention is directed to a block coded modulation or demodulation in digital communication, wherein a signal space diagram to which different numbers of bits are allocated is used. It is characterized in that digital modulation or demodulation is performed using signal points.

According to a second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, a plurality of types of transmission rate information are transmitted in order to suppress transmission errors. It is characterized in that it is encoded according to a spatial diagram and is transmitted prior to or consecutively with other encoded transmission information.

According to a third aspect of the present invention, in addition to the configuration of the second aspect of the present invention, in order to reduce transmission errors, a block code based on a set division method of a predetermined code length is used. And performing transmission using a multi-level code obtained by performing the first set division so as to include signal points of the signal space diagram to which a relatively small number of bits are assigned.

According to a fourth aspect of the present invention, in addition to the configuration of the second aspect of the present invention, a trellis wire determined in advance to facilitate the configuration of an apparatus using this method. It is characterized in that Viterbi decoding is performed according to the drawing.

According to a fifth aspect of the present invention, in addition to the configuration of the first aspect of the present invention, in order to facilitate a transmission procedure, various types of transmission speed information are encoded. Is transmitted together with the encoded transmission information, decoded according to a predetermined trellis diagram, and the above-described various types of transmission rate information are decoded, and the state of the trellis diagram is changed. It is characterized by being used as a part.

According to a sixth aspect of the present invention, in addition to the configuration of the fourth aspect of the present invention, a power of 2 to which the first number of bits is assigned for easy decoding is provided. Block coded modulation using a signal space diagram consisting of a first signal point group consisting of a number of signal points and a second signal point group consisting of signal points assigned a smaller number of bits than the first bit number In decoding in the scheme, a plurality of signal point groups obtained by the set division have a plurality of signal point groups having a common signal point, and one of the plurality of signal point groups is In the determined trellis diagram, a different sequence from the other signal point groups is assigned to the plurality of signal point groups.

[0013] The invention according to claim 7 provides the above-described claim 6 in order to easily decode even at different transmission speeds.
And Viterbi decoding using the above trellis diagram to obtain various types of transmission sequences according to the decoding result.

According to an eighth aspect of the present invention, in order to simplify the block code, a single type of block code is used in addition to the configuration of the first aspect of the present invention.
The transmission rate is changed only in one-way transmission.

The ninth aspect of the present invention is the first aspect of the present invention for simplifying the configuration of the encoder and the demodulator.
In addition to the configuration of the invention described in (1), the transmission rate is changed with the same number of transmission symbols by using a single type of encoder and demodulator.

As described above, according to the present invention, instead of changing the mode of the modem to change the transmission rate on the transmitting and receiving sides as in the prior art, the bit rate on the same signal space diagram surface on the same channel is reduced. A variable-rate transmission is realized by configuring a block coded modulation system in which different numbers of signal points are arranged, and by appropriately selecting these signal points, the Euclidean distance between the signal points is increased by increasing the number of signal points. , The transmission characteristics may be degraded, but this is avoided by using a block coded modulation method. At this time, the transmission bit information is also encoded and incorporated into the transmission code, or a method using set division is used to prevent an error in the number of transmission bits of the symbol. The present invention realizes a coded modulation / demodulation method with a variable transmission rate without using an index signal or dummy data of a transmission frame, that is, without a disadvantage that transmission efficiency is reduced.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the outline of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing a system configuration of an equivalent low-pass system. First, transmission data is block-coded. At this time, the bit number information of the transmission symbol may be encoded. Then, signal points are assigned by the increased set division method mapping, transmission symbols are created, and transmitted. The receiving side performs Viterbi decoding after synchronizing the symbols to obtain received data.

A method for realizing the above flow by 20QAM, multi-level block coding and modulation, and Viterbi decoding will be described below. FIG. 2 is a diagram illustrating signal point assignment of 20QAM. According to a well-known set division method, first, as shown in FIG. 2, four points on the x and y axes are used for 2-bit transmission, and the other parts are used for 4-bit transmission. Each bit assignment is also performed according to the set division method.
Further, α in the figure represents the amplitude ratio of the 2-bit transmission symbol to the 16QAM signal point constellation, is a real number with α> 0, and FIG. 2 shows the case where α = 1.

FIG. 3 shows the configuration of the block code used. In the following, this is represented by the symbol I. This is code length 6
Is a multi-level code that performs coding in the row direction from level 11 to level 13. And s1 to s in l1
A sequence obtained by encoding the number of 2-bit transmission symbols in 6 is arranged. However, the number of 2-bit symbols (m) is an even number from 0 to 6, and 2-bit symbols are arranged in s1 to s6 first from the left. FIG. 3 is an example where m = 2. The information transmission speed is 5/6 to 17/6 (bit / symbol).
c1 and c2 in l1 are m = 2 binary numbers, and c3
Is a parity of c3 = c1 + c2 (modulo 2) as shown in the figure. When the code length is L, the number of information bits is K, and the minimum Hamming distance is d, the block code is (L, K, d)
When expressed as a code, the entire l1 is a (6, 2, 4) duplicate code. That is, encoding of the minimum Hamming distance of 4 is performed for the identification of the number of bits of the transmission symbol. Also,
12 is a (6, 5, 2) parity code, which is coded regardless of the type of transmission bit number. 13 is an uncoded sequence, which is transmitted only when transmitting 4 bits.

The Euclidean distance between signal points is shown in FIG.
At

(Equation 1)

The code level li (i = 1, 2,
The square of the minimum Euclidean distance in 3) is

[0022]

(Equation 2)

The least square Euclidean distance (MS
ED) is as follows.

(Equation 3)

Here, MSED is described in the literature (D. Divs
alar and MKSimon, ≡The design of trellis coded
MPSK for fading channels: Performance criteria, ≡
IEEETrans.Commun., Vol36, pp. 1004-1012, Sep.
1988.). The larger the value of MSED, the better the bit error rate characteristics of the code under the white noise environment. Note that the transmission power of the 2-bit transmission symbol is

[0025]

(Equation 4)

Assuming that the average transmission power of a 4-bit transmission symbol is equal to the generation probability of a portion corresponding to 16 QAM,

[0027]

(Equation 5)

## EQU1 ## Therefore, when the generation probability of a 2-bit transmission symbol is p (0 ≦ p ≦ 1) and the transmission power is normalized, the value between α and d becomes

[0029]

(Equation 6) The following relationship holds. Α is determined by the equations (1) to (6).

Next, FIG. 5 shows an 8-state trellis diagram used for Viterbi decoding. In the figure, b1 to b4 are points in FIG. 2, and A1 to A4 are sets of signal points having the same branch.

A1 = (0, 1, 2, 3), A2 = (4, 5, 6, 7), A3 = (8, 9, 11, 12), A4 = (13, 14, 15, 16)

Therefore, the parallel path is Ai (1 ≦ i ≦
There are four branches in the branch that outputs 4). At the time of decoding, the metric of each nearest point in A1 to b4 of the received signal, that is, the square Euclidean distance is obtained along this trellis diagram. Then, a metric sum is obtained from the received signals of the s1 to s6 symbols by the Viterbi algorithm according to the branching rule shown in the figure, and the path giving the minimum value is determined as the decoding result.

As described above, the transmission point variable and the reduction of the bit error rate can be realized from the signal point arrangement using the set division method by increasing the signal points and the expansion of the MSED by using the block code.

Embodiments of the present invention will be described below in detail with reference to the drawings. First, the first embodiment is described with reference to FIGS.
Explanation will be made using 0.

FIG. 6 is a block diagram showing the equivalent low-frequency model used in the simulation. The channel is assumed to be an additive white Gaussian noise (AWGN) channel, and it is assumed that symbol synchronization and frame synchronization on the receiving side are perfect. When the number of bits assigned to one symbol is incorrect, a bit shift usually occurs in the same frame, and a burst-like bit error occurs later in the frame. However, in this state, it is difficult to compare the characteristics of the codes. Therefore, this time, the selection error of the number of transmission bits of the symbol is calculated as the symbol error rate (SER), and when calculating the bit error rate (BER), the excess bits in the same symbol are calculated. The missing bits are added as erroneous bits, but it has been assumed that deviations within the frame are avoided in some way.

FIGS. 7 and 8 show the results of calculating SER and BER with α = 0.4 and p = 0.5. p = 0.
The average information transmission speed at 5:00 is 11/6 (bit / symb
ol), and 2 (bit / sy) having a speed close thereto
The gain of about 2 dB is obtained for uncoded QPSK of (mbol). By adjusting the signal point arrangement in this way, a code with good characteristics was obtained.

FIG. 9 shows a code I in which the code length is extended to L = 15 and the minimum Hamming distance of l1 is set to 10. It is considered that this makes it possible to further reduce the selection error between the 4-bit and 2-bit points. The signal point assignment is the same, and the code structure is such that 11 is a (15,2,10) duplicate code, l2 is a (15,14,2) parity code, and 13 is an uncoded sequence. Information transmission speed is 14 / 15-44
/ 15 (bit / symbol). So MSE
D is as follows.

[0038]

(Equation 7)

FIG. 10 shows a trellis diagram of the code I where L = 15. In this case, the number m of 2-bit symbols is 0, 5,
10, 15, and similarly, 2-bit symbols are arranged from the left. Further, c1 and c2 are m / 5 binary numbers. The symbols in the figure are the same as in FIG. Since the configuration of the code is almost the same as when L = 6, the trellis diagram has the same configuration. FIG. 11 shows the calculation results. Since the Hamming distance for symbol type encoding is as large as 10, the SER is improved by about 2 dB and the BER is also improved by about 1 dB compared to the L = 6 sequence. Since the code length is slightly longer, the demodulation delay is larger than when L = 6, and a larger storage capacity is required. However, if these are not a problem, it is effective to increase the code length. Further, although there is a trade-off with the number of states of the trellis diagram, further improvement of the BER can be expected by encoding l3 or changing the sign of l2.

Next, a second embodiment will be described with reference to FIGS. In this embodiment, mixed transmission of 4 bits / symbol and 2 bits / symbol is performed using 24QAM. FIG. 12 shows signal point assignment of 24QAM. As shown in FIG. 12, 24 points are formed by adding eight points outside the signal points of 16 QAM. Bit allocation is based on the set division method shown in FIG. However, since 24 is not a power of 2, duplication occurs when 4 bits are allocated. Therefore, according to the set division method,
After the bits are assigned, the same code is assigned two by two with the outermost eight points assigned as two bits. Then, the minimum Euclidean distance between the 2-bit point and the 4-bit point is extended by the block code configuration. The code configuration in this case is shown in FIG. Hereinafter, this is referred to as symbol II. This code is a block code having a code length of 4, which performs encoding for each row of l1 to l3. When a block code having a code length L, the number of information bits K, and a minimum Hamming distance d is represented as an (L, K, d) code, l1 is a (4, 1, 4) duplicate code of a1 bits, l
1, 13 are (4, 3, 2) respectively as shown in the figure,
(8, 7, 2) parity code. Encoding is performed in units of blocks, but if only 2 bits are to be transmitted in any of the symbols s1 to s3, the corresponding point of the outermost shell in FIG. The encoding operation shown in FIG. 14 is performed. Since s4 includes a parity bit, 4-bit transmission is always performed.

Since there are eight outermost points, there are two possible ways of assigning them, which are selected by the value of the a1 bit of l1. FIG. 15 shows an example of encoding.
FIG. 15A shows an information bit sequence before encoding, and FIG. 15B shows a 4-bit sequence after encoding. 2
The bit sequence corresponds to the positions of the upper bits of l2 and l3 as shown in FIG.
The bit allocation of No. 7 uses a set division method for a set of parallel paths described later. By the above method, 4 (bit / symbol) and 2 (bit / symbol)
l) Mixed transmission can be performed. The positions of the 4-bit and 2-bit symbols in s1 to s3 are arbitrary.
In addition, since encoding is performed, the information transmission speed is 2 to 11
/ 4 (bit / symbol).

[0042] Here, when calculating the MSED sign II, since the 4Deruta ² to Δ in FIG. 13, the uncoded 2
A gain of 3 dB is obtained for 4QAM.

FIG. 16 shows a trellis diagram used for Viterbi decoding. A1 to B4 in the figure are sets of signal points having the same branch.

A1 = (0, 3), A2 = (1, 2, b3, b4), A3 = (4, 7), A4 = (5, 6, b7, b0), B1 = (8, 11, b5, b6), B2 = (9, 10), B3 = (12, 15, b1, b2), B4 = (13, 14),

Is as follows. Therefore, two or four parallel paths
The book will be there. In the above calculations, the 2-bit symbols and the 4-bit symbols in s1 to s3 have the same generation probability. In this case, the transmission rate is variable in frame units, but the average information transmission rate is 19/8 = 2.375 (bit)
/ Symbol). FIG. 17 shows SER, and FIG. 18 shows BER. However, the horizontal axis in FIGS. 16 and 17 is 24 QA
Average signal power to noise power density ratio per M transmission bit. FIG. 18 shows, as a comparison, uncoded QPSK,
The BER of the square lattice 8QAM is shown. Thus, the code I
Since I has the same configuration as that of the existing block coded modulation method using Viterbi decoding except that the 24QAM signal point constellation is used, it is considered that the demodulator can be easily configured.

[0046]

Since the present invention has the above-described configuration,
The following effects can be obtained.

According to the first aspect of the present invention, the transmission speed can be easily changed by using signal points to which different numbers of bits are assigned.

Further, according to the second and third aspects of the present invention, it is possible to reduce the transmission error rate by encoding the information including the transmission measure information.

According to the fourth aspect of the present invention, decoding can be easily performed.

Further, according to the fifth and sixth aspects of the present invention, the transmission rate can be easily changed by a predetermined algorithm.

According to the seventh aspect of the present invention, it is possible to easily decode transmission information having different transmission speeds.

Further, according to the present invention, the block code can be simplified.

According to the ninth aspect of the present invention, the configurations of the encoder and the demodulator can be simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a system configuration of an equivalent low-pass system.

FIG. 2 is a diagram illustrating 20QAM signal point assignment.

FIG. 3 is a diagram showing a block code (code I) having a code length of 6;

FIG. 4 is a diagram showing a Euclidean distance between signal points of 20QAM.

FIG. 5 is a diagram showing a trellis diagram of a symbol I.

FIG. 6 is a diagram showing a system configuration.

FIG. 7 is a diagram showing a symbol error rate characteristic of code I.

FIG. 8 is a diagram showing a bit error rate characteristic of code I.

FIG. 9 is a diagram showing a code I having a code length of 15;

FIG. 10 is a diagram showing a trellis diagram of a code I (L = 15).

FIG. 11 is a diagram illustrating error rate characteristics (L = 15, 6) of code I.

FIG. 12 is a diagram illustrating 24QAM signal point assignment.

FIG. 13 is a diagram showing assignment by a set division method.

FIG. 14 is a diagram showing a block code having a code length of 4 (code II).

FIGS. 15A and 15B are diagrams illustrating an example of encoding of a code II, and FIG.
FIG. 4 shows an information bit sequence before encoding, and FIG. 4B shows a 4-bit sequence after encoding.

FIG. 16 is a diagram showing a trellis diagram of a code II.

FIG. 17 is a diagram illustrating a symbol error rate characteristic of Code II.

FIG. 18 is a diagram showing a bit error rate characteristic of code II.

FIG. 19 is a diagram showing a first conventional method for realizing variable speed transmission using dummy data.

FIG. 20 is a diagram illustrating a second conventional method for realizing variable speed transmission using index information in a frame.

FIG. 21 is a diagram showing a third conventional method for achieving one-way variable transmission by devising a signal point arrangement.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J065 AD10 AH23 5K004 AA08 JA02 JD07

Claims (9)

[Claims] 1. A block rate modulation or demodulation in digital communication, wherein digital modulation or demodulation is performed using signal points of a signal space diagram to which different numbers of bits are assigned. Coded modulation demodulation method. 2. The method of claim 1, wherein a plurality of types of transmission rate information are coded according to the signal space diagram, and prior to the other coded transmission information, Alternatively, a coded modulation / demodulation method with a variable transmission rate, characterized by transmitting data continuously. 3. The coded modulation / demodulation method according to claim 2, wherein a block code based on a set division method of a predetermined code length is used, and the first set division is performed with a relatively small number of bits. A variable-rate coded modulation / demodulation method, characterized in that the transmission is performed using a plurality of levels of codes obtained by including the signal points of the signal space diagram to which the signal is assigned. 4. A method according to claim 2, wherein the Viterbi decoding is performed in accordance with a predetermined trellis diagram. . 5. The coded modulation / demodulation method according to claim 1, wherein various types of transmission rate information are coded and then transmitted together with the coded transmission information.
A transmission characterized in that the data is decoded according to a predetermined trellis diagram, and that the above-mentioned various kinds of transmission rate information are used as a part of the state of the trellis diagram after being decoded. A coded modulation / demodulation method with variable speed. 6. The method of claim 4, wherein the first signal point group is a power-of-two number of signal points to which a first number of bits is assigned;
A second signal point group consisting of signal points assigned a smaller number of bits than the first bit number, and a plurality of signals obtained by set division in decoding in a block coded modulation scheme using a signal space diagram consisting of: The point group has a plurality of signal point groups having a common signal point, and one of the plurality of signal point groups is represented by a plurality of signal point groups in a predetermined trellis diagram. A variable transmission rate coding / modulation / demodulation method, wherein a different sequence is assigned to another signal point group. 7. A method according to claim 6, wherein Viterbi decoding using said trellis diagram is performed to obtain various types of transmission sequences according to the decoding result. A coded modulation / demodulation method having a variable transmission rate, characterized by the following. 8. A variable-rate coded modulation system according to claim 1, wherein a single type of block code is used to change the transmission speed only in one-way transmission. Demodulation method. 9. A variable rate transmission system according to claim 1, wherein the transmission rate is changed with the same number of transmission symbols by using a single type of encoder and demodulator. Coded modulation demodulation method.