WO2012036366A1

WO2012036366A1 - Soft decision detection method and a decoding method using the same

Info

Publication number: WO2012036366A1
Application number: PCT/KR2011/003255
Authority: WO
Inventors: 김수영; 김영민
Original assignee: 전북대학교산학협력단
Priority date: 2010-09-15
Filing date: 2011-05-02
Publication date: 2012-03-22
Also published as: KR101060530B1

Abstract

Disclosed are a soft decision detection method and a decoding method using the same. In the decoding method, a send symbol is estimated by subjecting a receive symbol to STBC decoding, intermediate soft decision values are respectively calculated for the bits comprised in the estimated send symbol, and then final soft decision values are respectively calculated by multiplying the calculated soft decision values by a specific gain, and the estimated send symbol is repeatedly decoded by using the calculated final soft decision values. In this way, as compared with existing MLD techniques, it is possible to achieve a reduction in complexity while it is nevertheless also possible to achieve the same performance results.

Description

Soft Decision Detection Method and Decoding Method Using the Same

The present invention relates to a soft decision detection method and a decoding method using the same, and a soft decision detection method and a decoding method using the same in a system using a multi-antenna method using the STBC technology for obtaining the transmission diversity gain in a wireless communication system will be.

In a wireless communication system, the state of a channel may vary with time due to fading and interference occurring in the channel. In such an environment, by transmitting the same signal from a plurality of antennas in the transmitting end, the receiving end may combine the signals received from different channel environments to obtain diversity gain to improve the performance of the system.

Space-Time Block Coding (STBC) technology, which is a technology that obtains diversity gain by encoding and transmitting the same information in different forms at the same time in multiple antennas, was first proposed by Alamouti. .

This technique is designed to use two antennas at the transmitting end so that the coded form of the two symbols transmitted from each antenna is different during two symbol intervals, and the designed structure maintains orthogonality so that simple linear decoding is possible at the receiving end. It's a way to get a lot of diversity gain. Since then, various types of space-time block code techniques have been proposed.

The STBC technique is almost always used in combination with an error correction code in a wireless communication system. In the case of the error correction code method used in recent years, a method such as a turbo code that repeatedly performs decoding using a soft input / output signal is used. This is mainstream.

In this case, due to the characteristics of the turbo code for performing the above iterative decoding, the performance can be largely determined by how accurately the soft decision detection information is provided to the turbo code decoder.

Although maximum likelihood detection (MLD) provides the most accurate soft decision detection information in the STBC and error correction code combined system, it is possible to obtain the maximum performance, depending on the number of transmit antennas and the order of modulation symbols. Due to the exponentially increasing complexity, application in practical systems is almost impossible.

The present invention has been made to solve the above problems, an object of the present invention, the soft decision detection method that shows the same performance as the MLD while using a simple linear detection without using the MLD and the same, and using the same The present invention provides a decoding method.

In particular, in the case of using a combination of a space-time block code and an error correction code, it is possible to maximize the performance by detecting the soft decision value required by the error correction code in a very simple manner.

According to the present invention for achieving the above object, a decoding method comprises: estimating a transmission symbol by STBC decoding the received symbol; Calculating intermediate soft decision values for bits constituting the estimated transmission symbol, respectively; Calculating final soft decision values by multiplying the calculated soft decision values by a specific gain; And repeatedly decoding the estimated transmission symbol using the calculated final soft decision values.

The specific gain is preferably a gain reflecting a noise variance value changed by STBC decoding.

Further, the specific gain is preferably expressed as a function of the channel coefficients.

In the case of Alamouti STBC, in which the number of transmitting antennas is two and the number of receiving antennas is one, the channel coefficient is

H ₁ may be a channel coefficient between the first transmit antenna and the receiver, and h ₂ may be a channel coefficient between the second transmit antenna and the receiver.

In addition, in the case of the STBC proposed by Korea Patent Registration No. 10-0967954 (similar orthogonal space-time block code system and method) having four transmitting antennas and one receiving antenna, the final soft decision value

Is represented by the following equation,

Is the intermediate soft decision value, ρ ₁ and ρ ₂ are given by

ρ ₁ = 2 (α-β)

ρ ₂ = 2 (α + β)

h _i may be a channel coefficient between the i th transmit antenna and the receiver.

In the calculating of the intermediate soft decision values, the intermediate soft decision values may be calculated by using hard decision boundary values of bits constituting the estimated transmission symbol.

In addition, the decoding method is preferably applied to a wireless communication system using both STBC and error correction code.

On the other hand, the soft decision detection method according to the present invention, the step of calculating the respective intermediate soft decision values for the bits constituting the estimated transmission symbol; And calculating the final soft decision values by multiplying the calculated soft decision values by a specific gain.

On the other hand, according to the present invention, a reception apparatus includes: an STBC decoding unit for STBC decoding a received symbol to estimate a transmission symbol; A soft decision detector for calculating intermediate soft decision values for bits constituting the estimated transmission symbol, and multiplying the calculated soft decision values by a specific gain to calculate final soft decision values, respectively; And an iterative decoding unit for iteratively decoding the estimated transmission symbol using the calculated final soft decision values.

As described above, according to the present invention, there is an advantage that the same performance results can be obtained while reducing complexity compared with the conventional MLD scheme. In addition, there is an advantage that it is applicable to a multi-antenna system including various STBC schemes.

1 illustrates a wireless communication system to which the present invention is applicable;

2 is a flowchart provided to explain a decoding method according to an embodiment of the present invention;

3 is a diagram showing a table comparing the complexity of the scheme proposed in this embodiment and the MLD scheme, and

4 is a frame error rate performance comparison.

Hereinafter, with reference to the drawings will be described the present invention in more detail.

1 is a diagram illustrating a wireless communication system to which the present invention is applicable. A wireless communication system to which the present invention is applicable is a system using a space-time block coding (STBC) and an error correcting code together. The transmitter 100 and the receiver 200 are connected to each other so as to communicate with each other.

As shown in FIG. 1, the transmitter 100 constituting the wireless communication system includes an error correction coder 110, a modulator 120, and an STBC coder 130.

Error correction code unit 110, an error correction encoding the source of the binary signal converted to a binary vector b columns, and outputting the converted binary vector column b.

The modulator 120 performs baseband modulation on the binary vector string b . Specifically, the modulator 120 maps a plurality of bits as one symbol is converted into a symbol vector s heat, and outputs a transformed symbol column vector s.

The STBC coder 130 converts the symbol vector string s into s' by STBC encoding and transmits the result to the channel.

Meanwhile, fading generated in a channel may be mathematically modeled by the channel matrix H according to the number of transmit antennas and the number of receive antennas. In addition, it can be assumed that Gaussian noise n is added to the channel.

Accordingly, the receiver 200 receives the symbol vector string r to which the Gaussian noise n is added to the symbol vector string s' multiplied by the channel matrix H.

As shown in FIG. 1, the receiver 200 includes an STBC decoder 210, a soft decision detector 220, and an iterative decoder 230.

The STBC decoder 210 STBC decodes the received symbol vector string r to calculate an estimated value r ' for the transmitted symbol.

The soft decision detector 220 calculates the intermediate soft decision values b ' for the bits constituting the transmission symbol r' estimated by the STBC decoder 210 for each bit, and then multiplies a specific gain to obtain the final soft decision values b. Is calculated for each bit. Since the bit string b becomes a final soft decision vector sequence calculated based on r ' , that is, L ( b | r' ), the soft decision detector 220 converts the result into a vector sequence L ( b | r ' ). Output

The iterative decoder 230 iteratively decodes the vector string L ( b | r ' ) output from the soft decision detector 220 to restore the source binary signal.

Hereinafter, a process of decoding by the receiving apparatus 200 shown in FIG. 1 will be described in detail with reference to FIG. 2. 2 is a flowchart provided to explain a decoding method according to an embodiment of the present invention.

First, the STBC decoder 210 calculates an estimated value r ' for a symbol transmitted from the received symbol vector string r through linear algebra decoding using the coding matrix used by the STBC encoder 130 for STBC encoding ( S310).

Then, the soft decision detector 220 calculates the intermediate soft decision values b ' for the bits constituting the transmission symbol r' estimated by the STBC decoder 210 for each bit (S320).

In step S320, the intermediate soft decision values b ' are calculated using hard decision boundary values for bits constituting the estimated transmission symbol r' , and specific methods thereof are described by Sunheui Ryoo, Sooyoung Kim, and Sung Pal Lee. It is disclosed in "Efficient soft demapping method for high order modulation schemes (CIC 2003, Seoul, Korea)".

Thereafter, the soft decision detector 220 multiplies the calculated intermediate soft decision values b ' by a specific gain to calculate final soft decision values b for each bit (S330). The bit string b eventually r 'the final soft decision vector column L calculated based on (b | r' |, and outputs the result to the (r 'b)) is, the soft decision detection unit 220 is a vector column L so .

In step S330, the specific gain is a gain reflecting the noise variance value changed by STBC decoding, and is expressed as a function of channel coefficients that are elements of the channel matrix, and is expressed differently according to the number of transmitting antennas.

The iterative decoder 230 repeatedly decodes the vector string L ( b | r ' ) output from the soft decision detector 220 to restore the source binary signal (S340).

Hereinafter, a method of calculating a specific gain used in step S230 will be described in detail.

First, a process of calculating a specific gain in the case of using the STBC method using two transmitting antennas proposed by Alamouti will be described.

Equation 1 below shows a signal received during two symbol periods when using the method proposed by Alamouti.

Equation 1

Where * denotes a complex conjugate operation, r _i is a symbol received in the i th time slot and h _j is a channel coefficient between the j th transmit antenna and the receiver. As shown in Equation 1, the reception symbol r _i may be a symbol obtained by multiplying the transmission symbol x _i by a channel coefficient and adding a Gaussian noise n _i .

On the other hand, since the STBC coding matrix is an orthogonal matrix, the channel matrix is also an orthogonal matrix when Equation 1 is expressed using a channel matrix. Due to this characteristic, the transmission symbol estimation in the STBC decoder 210 of the receiver 200 may be performed by a simple linear operation as shown in Equation 2 below.

Equation 2

Transmission Symbol Estimated Using Equation 2

Since is composed of several bits, the soft decision value for each bit constituting the symbol must be obtained separately.

Estimated transmission symbol

Intermediate soft decision value for the j th bit constituting the

Has been described above that can be simply obtained using the hard decision boundary value.

Then, the intermediate soft decision value as shown in Equation 3 below

Certain benefits to

Multiply by the final soft decision value

Can be calculated.

Equation 3

Specific gain

Reflects the noise variance value changed during the STBC decoding process, and it can be seen that it is expressed as a function of channel coefficients.

Next, the process of calculating the specific gain in the case of using the quasi-orthogonal STBC method which can perform linear decoding is demonstrated.

Coding matrix for a pseudo-orthogonal STBC scheme capable of linear decoding for a wireless communication system using STBC proposed in Korean Patent Registration No. 10-0967954 (Similar Orthogonal Space-Time Block Code System and Method) using 4 transmitting antennas and 1 receiving antenna X _N4 and the corresponding channel matrix H _N4 may be represented by Equations 4 and 5 below.

Equation 4

Equation 5

Here, the transmission symbol estimated through STBC decoding

Can be obtained using Equation 6.

Equation 6

Here, H means Hermian operation on the matrix, ρ ₁ = 2 (α-β), ρ ₂ = 2 (α + β), and α and β are values representing the sum of channel gains and interference factors. It may be represented by Equation 7 below.

Equation 7

Estimated transmission symbol

Intermediate soft decision value for the j th bit constituting the

Then, the intermediate soft decision value as shown in Equation 8 below.

Multiplying the specific gain ρ ₁ (i = 1,2) or ρ ₂ (i = 3,4) by the final soft decision value Can be calculated.

Equation 8

The specific gain ρ ₁ (i = 1,2) or ρ ₂ (i = 3,4) reflects the noise variance value changed during the STBC decoding process, and it can be seen that it is expressed as a function of channel coefficients.

3 is a table comparing the complexity of the scheme proposed in this embodiment and the MLD scheme. As can be seen from FIG. 3, since the proposed scheme is based on linear detection, a very large complexity improvement can be obtained compared to the MLD scheme.

4 is a comparison diagram of frame error rate (FER) performance in a Rayleigh fading channel in a case where a turbo code having a frame size of 384 bits and an Alamouti scheme are combined in various modulation orders. 4, it can be seen that the proposed method in this embodiment can obtain the same result as the existing MLD method, which indicates that the proposed method shows the same performance as a complex operation with a simple operation. It can be said.

In addition, although the preferred embodiment of the present invention has been shown and described above, the present invention is not limited to the specific embodiments described above, but the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Of course, various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the prospect of the present invention.

The present invention relates to a soft decision detection method of a system using a multi-antenna method of a wireless communication system and a decoding method using the same.

Claims

STBC decoding the received symbol to estimate the transmitted symbol;

Calculating intermediate soft decision values for bits constituting the estimated transmission symbol, respectively;

Calculating final soft decision values by multiplying the calculated soft decision values by a specific gain; And

And repeatedly decoding the estimated transmission symbol by using the calculated final soft decision values.
The method of claim 1,

The specific gain,

A decoding method characterized by gain reflecting a noise variance value changed by STBC decoding.
The method of claim 2,

The specific gain,

And the channel coefficients are represented as a function of the channel coefficients.
The method of claim 3, wherein

In the case of Alamouti STBC, which has two transmit antennas and one receive antenna, the channel coefficient is
ego,

h 1 is the channel coefficient between the first transmit antenna and the receiver,

h 2 is a channel coefficient between the second transmit antenna and the receiver.
The method of claim 1,

If the number of transmitting antennas is four and the number of receiving antennas is one, the final soft decision value
Is represented by the following equation,

Is the intermediate soft decision value, ρ 1 and ρ 2 are given by

ρ 1 = 2 (α-β)

ρ 2 = 2 (α + β)

h i is a channel coefficient between the i th transmit antenna and the receiving end.
The method of claim 1,

Computing the intermediate soft decision values, respectively,

And calculating the intermediate soft decision values using hard decision boundary values for the bits constituting the estimated transmission symbol.
The method of claim 1,

The decoding method,

A decoding method characterized by being applied in a wireless communication system using both STBC and error correction code.
Calculating intermediate soft decision values for bits constituting the estimated transmission symbol, respectively; And

And multiplying the calculated soft decision values by a specific gain to calculate final soft decision values, respectively.
The method of claim 8,

The specific gain,

A soft decision detection method, characterized in that the gain reflects the noise variance value changed by STBC decoding.
The method of claim 9,

The specific gain,

Soft decision detection method characterized in that it is expressed as a function of said channel coefficients.
An STBC decoder which estimates a transmission symbol by STBC decoding the received symbol;

A soft decision detector for calculating intermediate soft decision values for bits constituting the estimated transmission symbol, and multiplying the calculated soft decision values by a specific gain to calculate final soft decision values, respectively; And

And an iterative decoding unit for iteratively decoding the estimated transmission symbol by using the calculated final soft decision values.