KR20130013984A - Cooperative transmission methods robust to frequency selective fading - Google Patents

Cooperative transmission methods robust to frequency selective fading Download PDF

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KR20130013984A
KR20130013984A KR1020110075962A KR20110075962A KR20130013984A KR 20130013984 A KR20130013984 A KR 20130013984A KR 1020110075962 A KR1020110075962 A KR 1020110075962A KR 20110075962 A KR20110075962 A KR 20110075962A KR 20130013984 A KR20130013984 A KR 20130013984A
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South Korea
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symbol
frequency selective
selective fading
node
cooperative
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KR1020110075962A
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Korean (ko)
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강승구
정다해
윤석호
박희만
박선
이연우
이성로
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목포대학교산학협력단
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/022—Site diversity; Macro-diversity
    • H04B7/026—Co-operative diversity, e.g. using fixed or mobile stations as relays
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/155—Ground-based stations
    • H04B7/15592—Adapting at the relay station communication parameters for supporting cooperative relaying, i.e. transmission of the same data via direct - and relayed path

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

The present invention relates to a cooperative transmission method that is robust to frequency selective fading. The cooperative transmission method according to the present invention provides a cooperative diversity gain through asynchronous cooperative communication in a frequency selective fading channel through a new cooperative transmission technique that is robust to frequency selective fading. It is characterized by obtaining. According to the present invention, in order to obtain a cooperative diversity gain in a frequency selective fading channel, the orthogonal matrix structure of the channel is finally obtained at the destination node by combining data blocks at the source node and recombining estimates of the combined blocks at the destination node. It is possible to obtain, to improve the phenomenon of not obtaining the cooperative diversity gain in the frequency selective fading channel, and to improve the system performance when establishing the cooperative communication in the actual wireless communication.

Description

Cooperative transmission methods robust to frequency selective fading

The present invention relates to a cooperative transmission method that is robust to frequency selective fading, and more particularly, to a method for obtaining cooperative diversity gain by using a plurality of mobile communication devices as a relay.

The cooperative communication system is a system for obtaining cooperative diversity gain by using a plurality of mobile communication devices as a relay, and can obtain diversity gain by using a space-time code having an orthogonal matrix structure of a channel at a destination node.

Since such a cooperative communication system uses a plurality of distributed mobile communication devices as relay nodes, there is a difference in arrival times between symbols transmitted from a source node and received at a destination node through each relay node, and thus, an asynchronous environment is naturally created. Cooperative diversity gain is obtained by obtaining the orthogonal matrix structure of the channel at the destination node using simple time-reversal operation and conjugate conjugate operation at the relay node.

However, this technique fails to obtain the orthogonal matrix structure of the channel at the destination node due to the influence of multipath components in frequency selective fading channels, and thus does not obtain the cooperative diversity gain and the bit error rate (BER). ) There is a problem of poor performance.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a cooperative transmission method that is robust to frequency selective fading to obtain cooperative diversity gain through asynchronous cooperative communication in a frequency selective fading channel through a new cooperative transmission technique that is robust to frequency selective fading. The purpose is to provide.

In order to achieve the above object, according to an aspect of the present invention, a cooperative transmission method that is robust to frequency selective fading between a source node, a destination node and at least two relay nodes includes: generating two data blocks at the source node; Generating a transport block by combining the generated two data blocks; Generating an OFDM transmission symbol by inserting a cyclic prefix for inter-symbol interference cancellation based on the generated transmission block and transmitting the OFDM symbol to each relay node; Each relay node performing an amplification operation on the received symbol; Obtaining, by the destination node, an estimate of the combined symbols transmitted from the source node after cyclic prefix removal of the symbol received through each relay node; And demodulating actual data symbols after recombination using the obtained estimates of the combined symbols.

According to the present invention, in order to obtain a cooperative diversity gain in a frequency selective fading channel, the orthogonal matrix structure of the channel is finally obtained at the destination node by combining data blocks at the source node and recombining estimates of the combined blocks at the destination node. Can be obtained.

In the frequency selective fading channel, the phenomenon of not obtaining cooperative diversity gain can be improved.

When establishing cooperative communication in real wireless communication, system performance can be improved.

1 is a view for explaining a cooperative transmission system according to an embodiment of the present invention.
2 is a diagram for explaining bit error rate performance.

Advantages and features of the present invention, and methods of achieving the same will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. And is intended to enable a person skilled in the art to readily understand the scope of the invention, and the invention is defined by the claims. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. It is noted that " comprises, " or "comprising," as used herein, means the presence or absence of one or more other components, steps, operations, and / Do not exclude the addition.

According to the present invention, a source node generates a new transport block by combining data blocks in a frequency domain, converts the generated new transport block into a time domain through an inverse discrete fourier transform (IDFT), and then relay node. In this case, the relay node performs a complex multiplication operation on the received symbol, transmits it to the destination node, performs a cyclic prefix (CP) removal operation on the received symbol, and then performs a discrete Fourier transform. After performing (DFT), performing decoding, and obtaining an estimate for a transmission signal through symbol recombination, it is demodulated using it.

Hereinafter, a cooperative transmission method robust to frequency selective fading according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. 1 is a view for explaining a cooperative transmission system according to an embodiment of the present invention, Figure 2 is a view for explaining the bit error rate performance.

As shown in FIG. 1, the cooperative communication system of the present invention includes a source node S, a destination node D, and at least two relay nodes R 1 and R 2 .

In this case, the relay node is described as an example, but the number is not limited thereto.

In the present invention, each L independent propagation paths include a channel between the source node S and each relay node R 1 and R 2 and a channel between each relay node R 1 and R 2 and the destination node D. Assume a frequency selective fading channel with

Nth channel impulse response between source node (S) and mth relay node (R m )

Figure pat00001
Is the same as Equation 1.

Figure pat00002

here

Figure pat00003
Is a delta function,
Figure pat00004
Wow
Figure pat00005
Is between the source node (S) and the m th relay node (R m ), respectively.
Figure pat00006
Channel coefficient and path delay value of the first propagation path, and the nth channel impulse response between the m th relay node (R m ) and the destination node (D).
Figure pat00007
Is the same as Equation 2.

Figure pat00008

here

Figure pat00009
Wow
Figure pat00010
Are each between the m th relay node (R m ) and the destination node (D).
Figure pat00011
Channel coefficient and path delay value of the first propagation path, and the channel coefficient
Figure pat00012
Wow
Figure pat00013
Variance with mean 0
Figure pat00014
Wow
Figure pat00015
It is modeled as an independent complex Gaussian random variable with.

Where each variance

Figure pat00016
It is assumed that the channel coefficient and the path delay value of each propagation path are maintained for two OFDM symbol intervals, and the relative arrival time difference between symbols transmitted from each relay node and reaching the destination node is satisfied.
Figure pat00017
Lt; / RTI >

In the source node (S), first the length

Figure pat00018
Pharyngeal Complex Data Symbol Block
Figure pat00019
and
Figure pat00020
Is generated as in Equation 3.

Figure pat00021

here

Figure pat00022
Is a phase shift keying (PSK) or quadrature amplitude modulation (QAM) located at the kth (k = 1,2, ..., n-1) subcarrier of the dth data symbol block. Means a data symbol modulated in a
Figure pat00023
Denotes a transposition operator.

A symbol combined using these data symbols

Figure pat00024
Is generated as shown in Equation 4.

Figure pat00025

In order to transmit the combined symbol blocks to each relay node R 1 and R 2 , transmission samples in the time domain are generated as shown in Equation 5 through a discrete inverse Fourier transform.

Figure pat00026

In order to prevent intersymbol interference (ISI), a CP is inserted and transmitted.

Figure pat00027
Is a symbol that occurs when the symbol arrives at the destination node (D) and the maximum path delay value of each path when the symbol reaches the destination node (D) from the source node (S) to the relay node (R 1 , R 2 ). The d-th OFDM transmission symbol with CP inserted, assuming longer than the sum of the maximum values of the relative arrival time differences between them
Figure pat00028
Is transmitted to the relay nodes R 1 and R 2 .

d-th received symbol at the m-th relay node (R m )

Figure pat00029
Is the same as Equation 6.

Figure pat00030

here

Figure pat00031
Denotes the transmit power at the source node S,
Figure pat00032
Denotes a channel vector between the source node S and the m th relay node R m during two OFDM transmission symbol intervals.
Figure pat00033
Is AWGN with mean 0, variance 1 added to the d-th received symbol at the m-th relay node (R m ),
Figure pat00034
Is the last two OFDM transmission symbol intervals (
Figure pat00035
Channel vector between the source node (S) and the m th relay node (R m )
Figure pat00036
Channel coefficient
Figure pat00037
Silver channel vector
Figure pat00038
of
Figure pat00039
It is modeled as a random variable with the same distribution as.

Channel vector between the m th relay node (R m ) and the destination node (D) during the last two transmission symbol intervals

Figure pat00040
The
Figure pat00041
Channel coefficient
Figure pat00042
Silver channel vector
Figure pat00043
of
Figure pat00044
It is modeled as a random variable with the same distribution as.

Each relay node (R 1 , R 2 ) is shown in Table 1,

Relay node 1 Relay node 2 First symbol to send

Figure pat00045
Figure pat00046
 Second symbol to send
Figure pat00047
Figure pat00048
 3rd symbol to send
Figure pat00049
Figure pat00050
 4th symbol to send
Figure pat00051
Figure pat00052

After processing the received symbols, the processed symbols are sequentially transmitted to the destination node (D). In Table 1

Figure pat00053
Denotes transmission power from the relay nodes R 1 and R 2 to the destination node D. FIG.

Figure pat00054

Figure pat00055

here

Figure pat00056
,
Figure pat00057
Denotes an AWGN with an average of 0 and a variance of 1 added to the d-th received symbol at the destination node D,
Figure pat00058
Denotes a cyclic convolution operation.
Figure pat00059
,
Figure pat00060
, And
Figure pat00061
Respectively
Figure pat00062
,
Figure pat00063
,And
Figure pat00064
, ≪ / RTI >
Figure pat00065
The
Figure pat00066
Is a vector of zeros.

Figure pat00067
and
Figure pat00068
The DFT output of Equation 9 and Equation 10 are as follows.

Figure pat00069

Figure pat00070

here

Figure pat00071
,
Figure pat00072
,
Figure pat00073
, And
Figure pat00074
Respectively
Figure pat00075
,
Figure pat00076
,
Figure pat00077
, And
Figure pat00078
The DFT output can be expressed in a matrix form as shown in Equation 11.

Figure pat00079

here

Figure pat00080
Wow
Figure pat00081
Respectively
Figure pat00082
Wow
Figure pat00083
The noise component of the channel matrix
Figure pat00084
Is the same as Equation 12.

Figure pat00085

here

Figure pat00086
ego,
Figure pat00087
Channel matrix
Figure pat00088
Is an orthogonal matrix structure, and the first and second transmitted symbols
Figure pat00089
Wow
Figure pat00090
Estimate of
Figure pat00091
Wow
Figure pat00092
Is as shown in Equation 13.

Figure pat00093

here

Figure pat00094
Means the complex transposition operator. In the processing in Table 1, the processing for the first symbol to be transmitted in the first relay and the processing for the symbol to be transmitted in the third are the same, and the processing for the second symbol to be transmitted Fourth and fourth estimates of the symbols transmitted because the processing for the symbol to be transmitted is the same
Figure pat00095
Wow
Figure pat00096
Is also obtained in the same manner.

The data symbols are obtained by recombining the estimates of the combined symbols thus obtained as shown in Equations 14 and 15.

Figure pat00097
Wow
Figure pat00098
Get an estimate of

Figure pat00099

Figure pat00100

As described above, according to the present invention, the orthogonal matrix of the channel is finally obtained through combining data blocks at the source node and recombining estimates of the combined blocks at the destination node to obtain cooperative diversity gain in the frequency selective fading channel. The structure can be obtained at the destination node, can improve the phenomenon of not obtaining the cooperative diversity gain in the frequency selective fading channel, and when establishing the cooperative communication in the actual wireless communication, as shown in FIG. 2, the bit error rate The performance of the system can be improved by improving the performance.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by the equivalents of the claims.

Claims (2)

A cooperative transmission method in which a source node, a destination node and at least two relays are robust to frequency selective fading between nodes,
Generating two data blocks at the source node;
Generating a transport block by combining the generated two data blocks;
Generating an OFDM transmission symbol by inserting a cyclic prefix for inter-symbol interference cancellation based on the generated transmission block and transmitting the OFDM symbol to each relay node;
Each relay node performing an amplification operation on the received symbol;
Obtaining, by the destination node, an estimate of the combined symbols transmitted from the source node after cyclic prefix removal of the symbol received through each relay node; And
Demodulating actual data symbols after recombination using the obtained estimates of the combined symbols;
A cooperative transmission method robust to frequency selective fading comprising a. In claim 1,
The step of transmitting to each relay node,
Inserting a cyclic prefix based on a maximum path delay of a frequency selective fading channel and a arrival time difference between symbols received at the destination node via each relay node after a discrete inverse Fourier transform,
Obtaining the estimate,
Performing a cyclic prefix removal operation on a symbol received at the destination node and converting the symbol block into a symbol block in a frequency domain through the Discrete Fourier Transform; And
Performing a complex prefix operation on an orthogonal channel matrix on the transformed symbol block to obtain an estimate of the transmitted combined symbols
Robust cooperative transmission method for frequency selective fading.
KR1020110075962A 2011-07-29 2011-07-29 Cooperative transmission methods robust to frequency selective fading KR20130013984A (en)

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