KR101674315B1 - A method for channel estimation in wireless communicatin systems with a distributed antenna structure - Google Patents

A method for channel estimation in wireless communicatin systems with a distributed antenna structure Download PDF

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KR101674315B1
KR101674315B1 KR1020150116184A KR20150116184A KR101674315B1 KR 101674315 B1 KR101674315 B1 KR 101674315B1 KR 1020150116184 A KR1020150116184 A KR 1020150116184A KR 20150116184 A KR20150116184 A KR 20150116184A KR 101674315 B1 KR101674315 B1 KR 101674315B1
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srs
channel
sequence
channel information
users
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KR1020150116184A
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Korean (ko)
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이용환
윤문형
변용석
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서울대학교산학협력단
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H04L25/0228—Channel estimation using sounding signals with direct estimation from sounding signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H04L25/0226—Channel estimation using sounding signals sounding signals per se

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

Abstract

The present invention relates to a method to estimate a channel by enabling a base station baseband signal processing module (hereinafter, referred to as a digital unit (DU)) using a massive multiple input multiple output antenna to use an uplink pilot signal as a sounding reference signal (SRS) in a wireless communication system with a distributed antenna structure in which the DU and an antenna module (hereinafter, referred to as a radio unit (RU)) are remotely separated. In an existing LTE/LTE-A system, a problem to reduce a channel estimating accuracy is generated by generating a pilot contamination phenomenon between the pilot signals by using the same SRS when the number of users is high in restricting the number of orthogonal SRS. Therefore, the present invention proposes the method to remarkably increase the number of SRS allocated to a user by using the SRS having a mutual relationship instead of the orthogonal SRS and to estimate a channel without reducing a performance in using the orthogonal SRS. The method comprises the steps of: enabling a DU to generate SRS used in estimating a channel to have a relationship from each other and to allocate the SRS to users; an RU to estimate channel information by receiving the SRS, transmitted by enabling the users to divide the whole subcarrier into SRS sequence period units, with the sequence period unit and to transmit the estimated channel information to the DU; and enabling the DU to finally estimate channel information between the RU and the terminal by using a relationship characteristic of the SRS from the channel estimation information transmitted by the RUs.

Description

TECHNICAL FIELD [0001] The present invention relates to a channel estimation method in a wireless communication system having a distributed antenna structure,

The present invention relates to a method for estimating channel information of a plurality of users using a cross correlation property of an SRS, which is an uplink pilot signal, in a wireless communication system having a large-scale distributed antenna structure.

The channel sounding using the uplink pilot in the time division duplex (TDD) system enables downlink channel information estimation through the channel reciprocity of the uplink / downlink characteristics. In recent years, in a large-scale multi-antenna technology and a distributed antenna system environment, which are attracting attention because they can increase a high transmission capacity and energy efficiency, when a downlink pilot signal is used, However, in TDD system, it is more efficient to use channel sounding method using fixed resources for each UE regardless of the number of antennas. In the process of transmitting an existing SRS, an SRS sequence orthogonal to each other is created, and the SRS sequence is allocated to each user, and the user transmits the SRS from the designated resource. Although the SRSs of several users are simultaneously transmitted from a predetermined resource, the base station can multiply the SRS sequence again for each user to eliminate the influence of another user and obtain the channel information of the corresponding user. Korean Patent Laid-Open No. 10-2008-0073191 (Channel Sounding Signal Transmission Apparatus and Method in a Radio Communication System) is a prior art related to channel sounding in a multi-antenna system based on a TDD system.

In the existing LTE / LTE-A system, orthogonal SRS is assigned to each user to perform channel sounding. However, since the number of orthogonal SRSs is limited according to the base sequence for generating the SRS, when the number of users increases, the SRSs that have already been used are reused and interference between pilots there is a problem that the accuracy of channel estimation is remarkably reduced due to contamination problems.

It is an object of the present invention to provide a channel estimation method using interference characteristics in a distributed antenna system using a large-scale multiple antenna. Thus, it is possible to greatly increase the number of SRSs that can be allocated to the user, thereby reducing the interference problem between reuse pilots, the channel estimation error, and SRS compatibility with the existing LTE-A system.

The operation principle of the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. And the definitions of the following terms should be based on the contents throughout this specification.

FIG. 1 is a wireless communication system model of a distributed antenna structure using a large-scale antenna considered in the present invention. In FIG. 1,

Figure 112015079934237-pat00001
,
Figure 112015079934237-pat00002
As shown in FIG. Referring to FIG. 1,
Figure 112015079934237-pat00003
And exchanges signals with the RUs 103 and 105 through a wired interface. RU
Figure 112015079934237-pat00004
,
Figure 112015079934237-pat00005
(103, 105)
Figure 112015079934237-pat00006
With multiple antennas
Figure 112015079934237-pat00007
,
Figure 112015079934237-pat00008
Service users,
Figure 112015079934237-pat00009
,
Figure 112015079934237-pat00010
(111, 113)
Figure 112015079934237-pat00011
,
Figure 112015079934237-pat00012
(103, 105)
Figure 112015079934237-pat00013
,
Figure 112015079934237-pat00014
(107,109)
Figure 112015079934237-pat00015
And the SRS is transmitted using the SRS. The RU receives the SRS transmitted by the users it services and the SRS of the users served by the neighboring RUs.

RU

Figure 112015079934237-pat00016
The subcarrier
Figure 112015079934237-pat00017
≪ / RTI >
Figure 112015079934237-pat00018
Can be expressed by the following equation (1).

Figure 112015079934237-pat00019

here

Figure 112015079934237-pat00020
Means a vector having an additive white Gaussian noise component with an average of 0,
Figure 112015079934237-pat00021
RU
Figure 112015079934237-pat00022
Users of
Figure 112015079934237-pat00023
And RU
Figure 112015079934237-pat00024
An independent and identically distributed complex Gaussian random variable channel vector having an average of 0 and a variance of 1 can be expressed by Equation (2).

Figure 112015079934237-pat00025

here

Figure 112015079934237-pat00026
Subcarrier
Figure 112015079934237-pat00027
RU at
Figure 112015079934237-pat00028
Users of
Figure 112015079934237-pat00029
And RU
Figure 112015079934237-pat00030
of
Figure 112015079934237-pat00031
Th antenna, and can be expressed by the following equation (3).

Figure 112015079934237-pat00032

At this time

Figure 112015079934237-pat00033
RU
Figure 112015079934237-pat00034
Users of
Figure 112015079934237-pat00035
And RU
Figure 112015079934237-pat00036
Is the channel path attenuation value between
Figure 112015079934237-pat00037
Is an iid complex Gaussian random variable with an average of 0 and a variance of 1. Received signal
Figure 112015079934237-pat00038
from
Figure 112015079934237-pat00039
The estimated channel value
Figure 112015079934237-pat00040
, The subcarrier
Figure 112015079934237-pat00041
Users in
Figure 112015079934237-pat00042
A normalized mean squared error (NMSE) of the estimated channel information of the channel estimation unit can be defined as Equation (4).

Figure 112015079934237-pat00043

The SRS orthogonal to each other in the existing LTE / LTE-A system is generated by the following Equation (5) to Equation (7). Cycle

Figure 112015079934237-pat00044
SRS
Figure 112015079934237-pat00045
≪ / RTI >
Figure 112015079934237-pat00046
Is cyclically shifted as shown in Equation (5).

Figure 112015079934237-pat00047

here

Figure 112015079934237-pat00048
Lt; / RTI >
Figure 112015079934237-pat00049
The
Figure 112015079934237-pat00050
, ≪ / RTI >
Figure 112015079934237-pat00051
The
Figure 112015079934237-pat00052
, And the reference sequence < RTI ID = 0.0 >
Figure 112015079934237-pat00053
Is defined by the following equation (6).

Figure 112015079934237-pat00054

here

Figure 112015079934237-pat00055
The
Figure 112015079934237-pat00056
The largest nonnegative prime,
Figure 112015079934237-pat00057
Is defined as a Zadoff-Chu sequence as shown in Equation (7).

Figure 112015079934237-pat00058

At this time

Figure 112015079934237-pat00059
Is an index associated with the physical cell ID (PCI) and SRS period of the base station.

As the number of users increases due to the use of large antennas, it is possible to increase the number of orthogonal SRS by using SRS having a long period, but it is susceptible to a frequency selective fading environment in addition to an increase in resources used. In the present invention, a method of using an SRS correlated with each other instead of using the orthogonal SRS is considered in order to efficiently service an extended user without increasing the sequence period.

FIG. 2 is a flowchart illustrating a method of generating a cross-correlation SRS according to an embodiment of the present invention in a TDD distributed antenna system having a large-scale multi-antenna. Referring to FIG. 2, the maximum number of SRSs having a small cross-correlation is calculated (201) based on a sequence period and a movement index in DU. And compares it to the required number of SRSs (203). If the number of users is less than the required number of SRSs (205)

Figure 112015079934237-pat00060
And generates SRS based on the generated SRS (209). Otherwise (207) is expressed by the following equation (8)
Figure 112015079934237-pat00061
(Step 209).

Figure 112015079934237-pat00062

here

Figure 112015079934237-pat00063
User index
Figure 112015079934237-pat00064
Wow
Figure 112015079934237-pat00065
Lt; RTI ID = 0.0 >
Figure 112015079934237-pat00066
Phase rotation may be applied to the reference sequence to generate an additional reference sequence. The generated SRSs are correlated with each other,
Figure 112015079934237-pat00067
It is possible to generate SRSs orthogonal to each other. The autocorrelation and cross-correlation of the SRS generated in Equation (8) are expressed by the following equations (9) and (10), respectively.

Figure 112015079934237-pat00068

Figure 112015079934237-pat00069

here

Figure 112015079934237-pat00070
to be.

RU

Figure 112015079934237-pat00071
A user of
Figure 112015079934237-pat00072
Can be estimated as shown in Equation (11) using the least squares estimation method of the related art.

Figure 112015079934237-pat00073

Where * is a complex conjugate,

Figure 112015079934237-pat00074
Lt;
Figure 112015079934237-pat00075
Is the subcarrier frequency in a certain section of the channel. In this case, the RU
Figure 112015079934237-pat00076
Users of
Figure 112015079934237-pat00077
Can be expressed by Equation (12). &Quot; (12) "

Figure 112015079934237-pat00078

The RU

Figure 112015079934237-pat00079
The user
Figure 112015079934237-pat00080
And transmits the data using a beam weight determined by Equation (13).

Figure 112015079934237-pat00081

The user < RTI ID = 0.0 >

Figure 112015079934237-pat00082
Can be expressed by Equation (14). &Quot; (14) "

Figure 112015079934237-pat00083

here

Figure 112015079934237-pat00084
User
Figure 112015079934237-pat00085
The subcarrier
Figure 112015079934237-pat00086
≪ / RTI >
Figure 112015079934237-pat00087
Represents a Gaussian noise. RU
Figure 112015079934237-pat00088
Users of
Figure 112015079934237-pat00089
Can be expressed by Equation (15). &Quot; (15) "

Figure 112015079934237-pat00090

Figure 112015079934237-pat00091
RU
Figure 112015079934237-pat00092
Users of
Figure 112015079934237-pat00093
And RU
Figure 112015079934237-pat00094
Lt; / RTI > is the channel path attenuation value between &
Figure 112015079934237-pat00095
Is an iid complex Gaussian random variable with an average of 0 and a variance of 1,
Figure 112015079934237-pat00096
Is the channel estimation mean squared error. The received signal given by Equation (14) can be expressed as Equation (16).

Figure 112015079934237-pat00097

RU

Figure 112015079934237-pat00098
Users of
Figure 112015079934237-pat00099
The signal-to-interference plus noise ratio (SINR)
Figure 112015079934237-pat00100
Quot; Cauchy-Schwarz inequality " can be expressed as Equation (17). &Quot; (17) "

Figure 112015079934237-pat00101

3 is a signal flow diagram illustrating an SRS transmission / reception and channel estimation method in a TDD distributed antenna system according to an embodiment of the present invention. Referring to FIG. 3, a plurality of RUs 303 are connected to DU 301 through an optical fiber connection, through which DU 301 controls each RU and user 305. DU 301 performs SRS generation and SRS cross correlation operation 307 and allocates 309 SRS for each RU 303 using the generated SRS. Each RU 303 assigns 311 an SRS to its user 305 and each user 313 transmits an assigned SRS. The channel information is estimated (315) using the SRS received for each RU 303 and the channel information estimated for each RU 303 is transmitted to the DU (317), and the DU (301) Finally, channel information is estimated (319).

The channel information estimation 319 process is as follows. The channel information estimated by Equation (11) can be expressed by Equation (18) in a block fading environment.

Figure 112015079934237-pat00102

The estimated channel information for all users can be expressed by Equation (19).

Figure 112015079934237-pat00103

here

Figure 112015079934237-pat00104
Is a channel estimated by the least squares estimation method of Equation (11)
Figure 112015079934237-pat00105
Is a channel estimated using interference channel information,
Figure 112015079934237-pat00106
Is the cross-correlation matrix between SRSs. DU can be obtained by the following equation (20).

Figure 112015079934237-pat00107

The conventional channel estimation error and the channel estimation error proposed by Equation (20) can be expressed by Equation (21) and Equation (22).

Figure 112015079934237-pat00108

Figure 112015079934237-pat00109

Comparing the errors of the two schemes in a block fading environment, the cooperative channel estimation method as shown in Equation (23) is superior in performance.

Figure 112015079934237-pat00110

Therefore, it is possible to support more users by using SRS with cross correlation without increasing the SRS cycle.

Equation (11) can be expressed as Equation (24) in a frequency selective fading environment.

Figure 112015079934237-pat00111

here

Figure 112015079934237-pat00112
Is a frequency correlation defined by the following equation (25).

Figure 112015079934237-pat00113

At this time

Figure 112015079934237-pat00114
Is an iid complex Gaussian random variable with an average of 0 and a variance of 1. Cross correlation matrix
Figure 112015079934237-pat00115
Can be expressed by the following equation (26).

Figure 112015079934237-pat00116

here

Figure 112015079934237-pat00117
to be. Equation (24) can be expressed as Equation (27) using Equation (26).

Figure 112015079934237-pat00118

here

Figure 112015079934237-pat00119
Can be expressed by the following equation (28)
Figure 112015079934237-pat00120
to be.

Figure 112015079934237-pat00121

At this time, the channel compensated by the interference is expressed by Equation (29).

Figure 112015079934237-pat00122

here

Figure 112015079934237-pat00123
Is a Minimum MSE (MMSE) nulling matrix, and can be expressed as Equation (30).

Figure 112015079934237-pat00124

At this time

Figure 112015079934237-pat00125
The
Figure 112015079934237-pat00126
Lt; / RTI > In the frequency selective fading environment, the error difference of the two channel estimation techniques can be expressed by Equation (31).

Figure 112015079934237-pat00127

The performance of the proposed cooperative channel estimation method is superior to that of the SRS with cross correlation even in the frequency selective fading environment. Therefore, it is possible to support more users with the proposed technique without increasing the SRS cycle.

4 is a flowchart illustrating an SRS allocation and a channel estimation method in a TDD distributed antenna system according to an embodiment of the present invention. Referring to FIG. 4, the maximum number of SRSs having a small cross-correlation is calculated 401, and a comparison 403 is performed to determine whether the required number of SRSs is greater than the maximum number of SRSs. If the number of required SRSs is greater than the maximum number of SRSs, an SRS having a small cross-correlation is allocated (405). If the number of users is less than the maximum number of SRSs, an SRS having a large cross-correlation is allocated (407). In each RU, the received signal is estimated (409) through LS, which is a conventional channel estimation method, and DU performs cooperative channel estimation (411) using the correlation information.

The present invention relates to a distributed antenna system using a large-scale multi-antenna system, in which SRS having a cross-correlation is used to increase the number of available SRSs, thereby reducing pilot reuse and cooperatively supplementing channel information using a cross- Can be accurately estimated. This can reduce channel estimation errors and maintain compatibility with existing LTE-A system SRS.

1 is an exemplary diagram of a wireless communication system according to an embodiment of the present invention.
2 is a diagram illustrating an example of a sounding sequence generation process according to an embodiment of the present invention.
3 is a signal flow diagram illustrating an SRS transmission / reception and channel estimation method in a TDD distributed antenna system according to an embodiment of the present invention.
4 is a flowchart illustrating an SRS allocation and a channel estimation method in a TDD distributed antenna system according to an embodiment of the present invention.

Claims (5)

A baseband signal processing base station (DU) using a multi-input multi-output transmits and receives signals using a plurality of radio transmission units (RUs) A channel estimation method for estimating channel information between an RU and a terminal in a wireless communication system having a distributed antenna structure,
Generating a sounding reference signal (hereinafter referred to as SRS) used by the DU to correlate with each other and allocating the sounding reference signal to users;
If the RU determines that the users are subscribed to the SRS sequence cycle
Figure 112016094250348-pat00128
Receiving the SRS divided in units of a sequence period to estimate channel information and transmitting the channel information to the DU;
And finally estimating channel information between the RU and the UE using the correlation property of the SRS from the channel estimation information transmitted by the DUs. The method according to claim 1,
The process of generating and correlating the SRSs used by the DUs to the users,
Cycle
Figure 112015079934237-pat00129
A cyclic shift sequence and a period
Figure 112015079934237-pat00130
By combining the Zadof-Chu sequences to create SRSs that correlate to each other,
Figure 112015079934237-pat00131
To a channel estimation method. 3. The method of claim 2,
Cycle
Figure 112016094250348-pat00132
Cyclic sequence movement sequence and cycle
Figure 112016094250348-pat00133
Combine in-zado-chu sequences to create SRSs that correlate to each other,
Figure 112016094250348-pat00134
Quot;
Cyclic shift sequence cycle
Figure 112016094250348-pat00135
SRS sequence cycle
Figure 112016094250348-pat00136
(Divisor) of the cyclic shift sequence index
Figure 112016094250348-pat00137
The
Figure 112016094250348-pat00138
And is phase noise.
Figure 112016094250348-pat00139
The
Figure 112016094250348-pat00140
, The user index < RTI ID = 0.0 >
Figure 112016094250348-pat00141
To
Figure 112016094250348-pat00142
;
Figure 112016094250348-pat00143
SRS sequence cycle
Figure 112016094250348-pat00144
When the largest prime among the smaller prime numbers,
Figure 112016094250348-pat00145
,
Figure 112016094250348-pat00146
The sequence cycle generated by
Figure 112016094250348-pat00147
In the commercial Zadoff-Chu sequence,
Figure 112016094250348-pat00148
Phase noise due to
Figure 112016094250348-pat00149
,
Figure 112016094250348-pat00150
The cycle generated by
Figure 112016094250348-pat00151
The SRS can be used to combine the cyclic shift sequences of the in-
Figure 112016094250348-pat00152
To create a user
Figure 112016094250348-pat00153
To a channel estimation method. The method according to claim 1,
If the RU determines that the users are subscribed to the SRS sequence cycle
Figure 112015079934237-pat00154
Receiving the SRS divided in units of a sequence period to estimate channel information and transmitting the channel information to the DU;
The RU receives the SRS using a conventional channel estimation scheme,
Figure 112015079934237-pat00155
≪ / RTI >
Figure 112015079934237-pat00156
Th sequence
Figure 112015079934237-pat00157
Channel information vector
Figure 112015079934237-pat00158
;
The RU estimates the channel information vector
Figure 112015079934237-pat00159
And transmitting the quantized signal to the DU. The method according to claim 1,
The process of finally estimating the channel information between the RU and the UE using the correlation property of the SRS from the channel estimation information transmitted by the DUs,
The DU,
Figure 112015079934237-pat00160
The terminal
Figure 112015079934237-pat00161
Lt; / RTI >
Figure 112015079934237-pat00162
The
Figure 112015079934237-pat00163
Indicated by
Figure 112015079934237-pat00164
The frequency correlation between subcarriers spaced by a predetermined distance,
Figure 112015079934237-pat00165
,
Figure 112015079934237-pat00166
The cross correlation matrix of the sounding signal,
Figure 112015079934237-pat00167
of
Figure 112015079934237-pat00168

;
The DU,
Figure 112015079934237-pat00169
Channel path attenuation,
Figure 112015079934237-pat00170
The matrix
Figure 112015079934237-pat00171
A Hermitian matrix,
Figure 112015079934237-pat00172
The matrix
Figure 112015079934237-pat00173
Inverse matrix,
Figure 112015079934237-pat00174
Is an iid complex Gaussian random variable with an average of 0 and a variance of 1,
Figure 112015079934237-pat00175
The
Figure 112015079934237-pat00176
(Covariance) matrix of a vector calculated by the following equation
Figure 112015079934237-pat00177

;
The DU calculates the channel information
Figure 112015079934237-pat00178
And channel estimation coefficient
Figure 112015079934237-pat00179
Using
Figure 112015079934237-pat00180
And finally estimating the channel information using the channel estimation method.
KR1020150116184A 2015-08-18 2015-08-18 A method for channel estimation in wireless communicatin systems with a distributed antenna structure KR101674315B1 (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108923903B (en) * 2018-06-26 2020-06-05 北京邮电大学 Pilot frequency distribution method and system for multi-antenna system and electronic equipment
WO2023249356A1 (en) * 2022-06-23 2023-12-28 삼성전자 주식회사 Device and method for fronthaul transmission in wireless communication system

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20110091394A (en) * 2010-02-05 2011-08-11 삼성전자주식회사 Apparatus and method to transmit/receive sounding signal in a wireless communication system
KR20140093554A (en) * 2013-01-18 2014-07-28 주식회사 케이티 System and method for control of load balanced transmission in wireless communication system

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20110091394A (en) * 2010-02-05 2011-08-11 삼성전자주식회사 Apparatus and method to transmit/receive sounding signal in a wireless communication system
KR20140093554A (en) * 2013-01-18 2014-07-28 주식회사 케이티 System and method for control of load balanced transmission in wireless communication system

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108923903B (en) * 2018-06-26 2020-06-05 北京邮电大学 Pilot frequency distribution method and system for multi-antenna system and electronic equipment
WO2023249356A1 (en) * 2022-06-23 2023-12-28 삼성전자 주식회사 Device and method for fronthaul transmission in wireless communication system

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