WO2010077041A2

WO2010077041A2 - Method and apparatus for transmission of sounding reference signal in uplink wireless communication system with muti-carrier transmission scheme

Info

Publication number: WO2010077041A2
Application number: PCT/KR2009/007834
Authority: WO
Inventors: Sang Min Ro; Jae Chon Yu; Joon Young Cho
Original assignee: Samsung Electronics Co., Ltd.
Priority date: 2008-12-29
Filing date: 2009-12-28
Publication date: 2010-07-08
Also published as: KR20100077401A; KR101581756B1; WO2010077041A3

Abstract

A method and apparatus are provided for transmission of a sounding reference signal (SRS) in an uplink wireless communication system with a multi-carrier transmission scheme. A user equipment terminal receives a subframe offset among component carriers of an uplink channel from a base station. Then the user equipment terminal determines a particular subframe configured for transmission of the SRS in the respective component carriers, depending on the subframe offset. The user equipment terminal assigns the SRS to the component carriers corresponding to the particular subframe, and transmits the particular subframe to the base station. Since the subframe offset among component carriers may be changed, every user equipment terminal may cope flexibly with variable conditions such as channel states and power limitations.

Description

METHOD AND APPARATUS FOR TRANSMISSION OF SOUNDING REFERENCE SIGNAL IN UPLINK WIRELESS COMMUNICATION SYSTEM WITH MUTI-CARRIER TRANSMISSION SCHEME

The present invention relates in general to a method and apparatus for transmission of a sounding reference signal (SRS) in an uplink wireless communication system with a multi-carrier transmission scheme and, more particularly, to a method and apparatus for transmitting a sounding reference signal by setting subframe indexes of a plurality of component carriers in an uplink wireless communication system with a multi-carrier transmission scheme.

A single carrier transmission technique is used as one of technologies to enhance uplink coverage in wireless communication systems. For example, Long Term Evolution (LTE), one of next generation mobile communication systems introduced in the third Generation Partnership Project (3GPP), employs a Single Carrier Frequency Division Multiple Access (SC-FDMA) based uplink so as to increase coverage and reduce power consumption in terminals.

A mobile user equipment terminal transmits a sounding reference signal (SRS) through the whole system bandwidths of uplink. A fixed base station receives SRS and acquires channel state information about uplink bandwidths. Based on such information, a base station performs frequency selective scheduling, power control, timing estimation, modulation and coding scheme (MCS) level selection, etc.

The LTE-Advanced (LTE-A) system, which is an upgrade version of the LTE, is designed to support the maximum system bandwidth reaching 100MHz. Additionally, the LTE-A system admits a multi-carrier transmission scheme to improve a bit rate and to allow a flexible allocation of uplink resources.

As a user of the LTE system coexists with a user of the LTE-A system, interoperability between both systems is being discussed in the art. One of strong proposals is to compose the LTE-A uplink system bandwidth from integration of component carriers each of which corresponds to the LTE uplink system bandwidth. This may allow LTE users to continuously use the existing LTE service in a single component carrier, and also, may allow LTE-A users to use their service through at least one component carrier. Considering that the maximum bandwidth of the LTE system is 20MHz, the LTE-A system may also set the maximum bandwidth of each component carrier up to 20MHz.

However, in case where a sounding reference signal is transmitted through all component carriers, a base station may receive sounding reference signals with low power densities from LTE-A terminals located at peripheral parts of a cell. Therefore, the reliability of channel state information on uplink obtained from such sounding reference signals may be lowered. Unfortunately, this may obstruct an efficient uplink control in a base station.

An aspect of the present invention is to address the above-mentioned problems and/or disadvantages and to provide at least the advantages described below.

Accordingly, an aspect of the present invention is to provide a sounding reference signal transmission technique which may allow a reduction in transmitting power consumption and an increase in reliability of a sounding reference signal in case where mobile user equipment transmits a sounding reference signal through a wide bandwidth composed of a plurality of component carriers in an uplink system with a multi-carrier transmission scheme.

According to one aspect of the present invention, provided is a method for transmitting a sounding reference signal (SRS) at a user equipment terminal in an uplink wireless communication system with a multi-carrier transmission scheme, the method comprising: receiving a subframe offset among component carriers of an uplink channel from a base station; determining a particular subframe configured for transmission of the SRS in the respective component carriers, depending on the subframe offset; assigning the SRS to the component carriers corresponding to the particular subframe; and transmitting the particular subframe to the base station.

According to another aspect of the present invention, provided is a method for receiving a sounding reference signal (SRS) at a base station in an uplink wireless communication system with a multi-carrier transmission scheme, the method comprising: determining a subframe offset among component carriers of an uplink channel, depending on a state of the uplink channel; transmitting the subframe offset to a user equipment terminal; receiving a subframe from the user equipment terminal; and extracting the SRS from the component carriers corresponding to the received subframe, depending on the subframe offset.

According to still another aspect of the present invention, provided is an apparatus for transmitting a sounding reference signal (SRS) in an uplink wireless communication system with a multi-carrier transmission scheme, the apparatus comprising: an SRS generator configured to create the SRS by using cyclic shift values assigned from a base station; and a frequency assignor configured to determine a particular subframe selected for transmission of the SRS in respective component carriers of an uplink channel by depending on a subframe offset among the component carriers, the subframe offset being received from the base station, and configured to assign the SRS to the component carriers corresponding to the particular subframe.

According to yet another aspect of the present invention, provided is an apparatus for receiving a sounding reference signal (SRS) in an uplink wireless communication system with a multi-carrier transmission scheme, the apparatus comprising: a means for determining a subframe offset among component carriers of an uplink channel by depending on a state of the uplink channel; a means for transmitting the subframe offset to a user equipment terminal and for receiving a subframe from the user equipment terminal; and a means for extracting the SRS from the component carriers corresponding to the received subframe, depending on the subframe offset.

Therefore, aspects of the present invention may transmit sounding reference signals suitably for channel conditions, reduce transmitting power consumption in terminals, and increase the reliability of sounding reference signals.

Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

FIG. 1 is a view which illustrates a case of LTE uplink system transmission.

FIG. 2 is a view which illustrates a case of LTE-A uplink system transmission.

FIG. 3 is a view which illustrates a case where an LTE-A user equipment terminal transmits a sounding reference signal through a plurality of component carriers.

FIG. 4 is a view which illustrates transmission of sounding reference signals in accordance with an exemplary embodiment of the present invention.

FIG. 5 is a view which illustrates transmission of sounding reference signals in accordance with another exemplary embodiment of the present invention.

FIG. 6 is a view which illustrates transmission of sounding reference signals in accordance with still another exemplary embodiment of the present invention.

FIG. 7 is a block diagram which illustrates a configuration of a user equipment terminal in accordance with an exemplary embodiment of the present invention.

FIG. 8 is a block diagram which illustrates a configuration of a base station in accordance with an exemplary embodiment of the present invention.

FIG. 9 is a flow diagram which illustrates a process of signal transmission at a user equipment terminal in accordance with an exemplary embodiment of the present invention.

FIG. 10 is a flow diagram which illustrates a process of signal reception at a base station in accordance with an exemplary embodiment of the present invention.

Exemplary, non-limiting embodiments of the present invention will now be described more fully with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, the disclosed 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. The principles and features of this invention may be employed in varied and numerous embodiments without departing from the scope of the invention.

Furthermore, well known or widely used techniques, elements, structures, and processes may not be described or illustrated in detail to avoid obscuring the essence of the present invention. Although the drawings represent exemplary embodiments of the invention, the drawings are not necessarily to scale and certain features may be exaggerated or omitted in order to better illustrate and explain the present invention.

Although the LTE-A system is exemplarily employed for the following description, the present invention is not limited thereto. It will be understood by those skilled in the art that the present invention may be favorably applied to any case where mobile user equipment transmits a sounding reference signal in a wide bandwidth composed of a plurality of component carriers in all uplink systems with a multi-carrier transmission scheme.

FIG. 1 is a view which illustrates a case of LTE uplink system transmission.

Referring to FIG. 1, a subframe 100 with 1ms duration, which is a unit of LTE uplink transmission, is composed of two slots 101 each of which is 0.5ms long. Considering generally the length of cyclic prefix (CP), each individual slot has seven symbols 102 each of which corresponds to a single SC-FDMA symbol. A resource block (RB) 103 is a resource allocation unit, which corresponds to twelve subcarriers in the frequency domain and a single slot in the time domain.

An uplink structure in the LTE is classified into a data region 104 and a control region 105. The data region 104 refers to a sequence of communication resources which include data, such as a voice and a packet, to be transmitted to respective user equipment terminals. The data region 104 coincides with the remaining resources of the subframe 100 except the control region 105. The control region 105 refers to a sequence of communication resources which include downlink channel quality indication, reception acknowledgement and non-acknowledgement (ACK/NACK) for downlink signals, uplink scheduling requests, etc. from respective user equipment terminals.

As indicated by a reference number 106, a time for transmission of a sounding reference signal (SRS) in a single subframe is defined as a block of the last SC-FDMA symbol on a time axis in a single subframe, and also, SRS transmission is made through the data region 104 on a frequency axis. Such sounding reference signals of several user equipment terminals transmitted through the last SC-FDMA of a single subframe may be distinguished from each other according to their frequency location.

A sounding reference signal is formed of a Constant Amplitude Zero Auto Correlation (CAZAC) sequence. Sounding reference signals transmitted from several user equipment terminals are different CAZAC sequences with different cyclic shift values. Each individual CAZAC sequence is created by cyclic shift from one CAZAC sequence and has a zero correlation value with the other sequences which are different in cyclic shift value. Therefore, sounding reference signals in the same frequency bandwidth can be distinguished from each other according to cyclic shift values of their CAZAC sequences. A sounding reference signal of each user equipment terminal is assigned onto the frequency domain, depending on a tree structure defined by a base station. A user equipment terminal performs a frequency hopping of a sounding reference signal so that a sounding reference signal can be transmitted through the entire uplink data transmission bandwidth within this tree structure.

FIG. 2 is a view which illustrates a case of LTE-A uplink system transmission.

Referring to FIG. 2, an uplink system bandwidth 200 is divided into five component carriers 201, also referred to as chunks, each of which has a bandwidth of 20MHz. Each component carrier 201 is composed of a data region 202 and a control region 203, just like the transmission structure of LTE uplink shown in FIG. 1. That is, in order to accept users of the existing LTE system, each component carrier 201 in the LTE-A system has the same uplink transmission structure as the LTE system has.

Although FIG. 2 exemplarily shows the control region 203 located at only both ends of the entire system bandwidth 200, it is alternatively possible to place the control region 203 at both ends of each component carrier 201 as shown in FIG. 1. Additionally, a guard band 204 may be arranged between the adjacent component carriers 201 so as to reduce interference therebetween. An SRS transmission region 205 configured for transmission of sounding reference signals in the LTE-A uplink system employs the last block on a time axis and the data region 202 on a frequency axis in a subframe. This resembles a case of the LTE uplink system shown in FIG. 1, thus maintaining interoperability with the LTE system.

Referring to FIG. 3, it is supposed that an uplink system bandwidth 300 is 100MHz and each component carrier 301 has the bandwidth of 20MHz. As shown, an LTE-A user equipment terminal performs a frequency hopping of sounding reference signals at every transmission time (i.e., 1st SRS transmission and 2nd SRS transmission in FIG. 3), and transmits sounding reference signals 306 through a

data region

302 or 305 of each component carrier 301.

As discussed above, if the LTE-A user equipment terminal follows a typical LTE configuration to transmit a sounding reference signal 306 for each component carrier 301, the LTE-A user equipment terminal comes to employ a multi-carrier transmission scheme which may invite an increase in power consumption. Furthermore, if transmission of sounding reference signals occurs at a time in all component carriers 301, a base station may receive sounding reference signals with low power densities from LTE-A user equipment terminals located at peripheral parts of a cell. The reliability of channel state information obtained from such sounding reference signals may be therefore lowered, and this may obstruct an efficient uplink control in a base station.

In order to solve the above problems, the present invention defines the offset of transmission time for sounding reference signals in respective component carriers instead of simultaneously transmitting sounding reference signals through several component carriers. Otherwise, if a user equipment terminal is located at central parts of a cell, namely, if multi-carrier transmission does not cause serious problems such as high power consumption in terminals and poor reliability of sounding reference signal reception, the present invention defines the subframe offset in respective component carriers to simultaneously transmit sounding reference signals through several component carriers.

FIG. 4 is a view which illustrates transmission of sounding reference signals in accordance with an exemplary embodiment of the present invention. In particular, FIG. 4 is a case where LTE-A user equipment terminals transmit sounding reference signals under power limitations.

Referring to FIG. 4, a system bandwidth of the LTE-A uplink is composed of five

component carriers

400, 401, 402, 403 and 404. Each component carrier has a bandwidth of 20MHz, including a guard band. In order to accept LTE users, each component carrier adopts the existing LTE configuration for SRS transmission. A subframe allowing LTE user equipment to transmit sounding reference signals (SRS) is determined according to both cell specific and UE specific signaling from base station. The cell specific configuration indicates subframes where LTE UEs in the cell can transmit SRS. The UE specific signaling informs each LTE UE the particular subframe where each LTE UE should transmit SRS among subframes configured by cell specific configuration. That is a base station notifies each user equipment terminal which subframe is selected for SRS transmission. It is supposed in this embodiment that different subframes for SRS transmission are assigned to the respective component carriers.

For example, as shown in FIG. 4, a subframe configured for SRS transmission in the first component carrier 400 is determined as first and second subframes among five subframes within the period of 5ms (i.e., subframe offset {0, 1}). Therefore, certain LTE user equipment (LTE UE) selects one offset between two subframes and performs SRS transmission, depending on the aforesaid signaling from a base station. In a case of the second component carrier 401, the LTE UE sends sounding reference signals through the second subframe between two subframes within the period of 2ms (i.e., subframe offset {1}).

On the other hand, it is further supposed that a sounding reference signal 406 from the first LTE-A user equipment (LTE-A UE 1) is transmitted through the first subframe among five subframes in every component carrier, and the subframe offset between adjacent component carriers is set to one subframe. Therefore, a sounding reference signal 406 from the LTE-A UE 1 is transmitted through the first subframe (subframe 0) in the first component carrier 400 and then through the second subframe (subframe 1) in the second component carrier 401. In the same way, a sounding reference signal 406 from the LTE-A UE 1 is transmitted in only one component carrier at each SRS transmission time.

Therefore, the LTE-A UE 1 meets a single-carrier property during SRS transmission, reducing power consumption in comparison with a case of FIG. 3. Additionally, since SRS transmission requires smaller frequency bandwidth than ever, power density of sounding reference signals on the frequency domain is relatively increased. This may allow a base station to receive sounding reference signals with enhanced reliability. Accordingly, this embodiment may be useful for SRS transmission in case where mobile user equipment terminals are under power limitations, for example, in case of being located at peripheral parts of a cell.

With regard to a sounding reference signal 407 from the second LTE-A user equipment (LTE-A UE 2), the subframe offset between adjacent component carriers is set to four subframes. That is, a sounding reference signal 407 from the LTE-A UE 2 is transmitted through the second subframe (subframe 1) in the first component carrier 400 and then through the sixth subframe (subframe 5) in the second component carrier 401. In this case as well, SRS transmission occurs in only one component carrier at a time, so favorable improvements are expected in power consumption and the reliability of SRS reception.

FIG. 5 is a view which illustrates transmission of sounding reference signals in accordance with another exemplary embodiment of the present invention. In particular, FIG. 5 is a case where LTE-A user equipment terminals transmit sounding reference signals under little power limitations.

Referring to FIG. 5, it is supposed that a sounding reference signal 506 from the LTE-A UE 1 is transmitted once every two subframes in each individual component carrier, and the subframe offset among the first to the third component carriers 500 to 502 is set to zero. In addition, it is further supposed that the fourth and the

fifth component carriers

503 and 504 are set to be transmitted one subframe later than the first to the third component carriers 500 to 502. Therefore, the LTE-A UE 1 transmits a sounding reference signal 506 through several component carriers at a time and fails to meet a single-carrier property.

Accordingly, in comparison with a case of FIG. 4, power consumption is increased and power density of sounding reference signals on the frequency domain is relatively reduced. Therefore, this embodiment may be useful for SRS transmission in case where mobile user equipment terminals are under good channel states, for example, in case of being located at central parts of a cell.

A sounding reference signal 507 from the LTE-A UE 2 is transmitted once every five subframes in each individual component carrier. In addition, the fourth and the

fifth component carriers

503 and 504 are set to be transmitted three subframes later than the first to the third component carriers 500 to 502.

Referring to FIG. 6, a sounding reference signal 606 from the LTE-A UE 1 has the same SRS transmission scheme as in a case of FIG. 5. The LTE-A UE 2 has a worse channel state than the LTE-A UE 1, but has a better channel state than in a case of FIG. 4.

In this case, a sounding reference signal 607 from the LTE-A UE 2 is transmitted through the first and the

second component carriers

600 and 601. Additionally, each of the third to the fifth component carriers 602 to 604 has the subframe offset of one subframe with the adjacent component carrier. In view of power consumption and SRS reception reliability, this case may be applied to middle conditions between cases of FIGS. 4 and 5. As discussed heretofore, the present invention may allow every LTE-A user equipment to cope flexibly with variable conditions such as channel states and power limitations by changing the subframe offset among component carriers.

Referring to FIG. 7, the mobile user equipment terminal includes a sounding reference signal (SRS) setter 700, an SRS sequence generator 701, an SRS sequence cyclic shift value storage 702, a cyclic shifter 703, an SRS frequency hopping pattern generator 704, a frequency assignor 705, an Inverse Fast Fourier Transformer (IFFT) 706, a cyclic prefix (CP) inserter 707, and an antenna 708.

The SRS setter 700 performs a cell specific setting and an UE specific setting for sounding reference signals, depending on information received from a base station. Then the SRS setter 700 determines the SRS transmission timing. In particular, the SRS setting unit 700 defines the subframe offset among component carriers to determine the SRS transmission timing. That is, the SRS setter 700 determines which component carrier is employed for SRS transmission at the corresponding transmission timing. In addition, The SRS sequence cyclic shift value storage 702 stores SRS sequence indexes and cyclic shift values assigned to user equipment terminals by a base station.

The SRS sequence generator 701 creates an SRS sequence at the SRS transmission timing which is determined by the SRS setter 700. The cyclic shifter 703 shifts SRS sequences by using SRS sequence indexes and cyclic shift values stored in the SRS sequence cyclic shift value storage 702.

The SRS frequency hopping pattern generator 704 determines a particular region of the frequency domain for SRS transmission and then creates a frequency hopping pattern. Here, the SRS frequency hopping pattern is a predefined pattern between a base station and mobile user equipment. The frequency assignor 705 assigns the frequency location of sounding reference signals to respective component carriers, based on the SRS frequency hopping pattern and initial SRS frequency assigning information received from a base station.

The IFFT 706 transforms the frequency domain of sounding reference signals into the time domain. The CP inserter 707 inserts cyclic prefixes for preventing data error into sounding reference signals and then outputs the signals through the antenna 708.

Referring to FIG. 8, the base station includes a cyclic prefix (CP) remover 800, a Fast Fourier Transformer (FFT) 801, a sounding reference signal (SRS) setter 802, an SRS frequency hopping pattern generator 803, a first SRS extractor 804, an SRS sequence cyclic shift value storage 805, a second SRS extractor 806, and an uplink channel measurer 807.

The CP remover 800 removes cyclic prefixes from sounding reference signals received from mobile user equipment. The FFT 801 transforms the time domain of sounding reference signals into the frequency domain.

The SRS setter 802 performs a cell specific setting and an UE specific setting for sounding reference signals. The SRS frequency hopping pattern generator 803 creates a frequency hopping pattern predefined between a base station and mobile user equipment. The first SRS extractor 804 extracts sounding reference signals of user equipment terminals from the frequency domain, using the cell specific setting information, the UE specific setting information, and the frequency hopping pattern.

The SRS sequence cyclic shift value storage 805 stores SRS sequence indexes and cyclic shift values assigned to user equipment terminals by a base station. The second SRS extractor 806 separates sounding reference signals multiplexed in the same frequency domain from the code domain, using SRS sequence indexes and cyclic shift values. The uplink channel measurer 807 estimates uplink channel states through sounding reference signals of each user equipment terminal and then employs it for uplink control.

Referring to FIG. 9, the user equipment (UE) terminal receives broadcast signals such as a system information block (SIB) from a base station and then acquires cell specific SRS transmission setting information contained therein (step 900). Here, each individual UE terminal in a cell recognizes a particular subframe configured for SRS transmission, depending on cell specific SRS transmission setting information. Then the UE terminal determines the SRS transmission timing, depending on the UE specific SRS transmission setting information and the subframe offset information about component carriers (step 901).

Next, the UE terminal determines whether the current subframe meets an SRS transmission timing, based on information acquired in the above steps 900 and 901 (step 902). In case of non SRS transmission timing, the UE terminal turns off the SRS sequence generator (step 903) and then sends data or control information (step 904). In case of SRS transmission timing, the UE terminal turns on the SRS sequence generator and then creates an SRS sequence based on SRS sequence indexes and cyclic shift values (step 905).

Next, the UE terminal determines which component carrier is employed for SRS transmission, depending on the subframe offset information about component carriers, and then assigns the frequency location of SRS to respective component carriers, depending on the SRS frequency hopping pattern and initial SRS frequency assigning information received from a base station (step 906). Thereafter, the UE terminal transmits SRS to a base station through the antenna (step 907).

Referring to FIG. 10, the base station determines whether an SRS transmission subframe is received from the UE terminal (step 1000). If no SRS transmission subframe is received, the base station receives data or control information (step 1001).

If an SRS transmission subframe is received, the base station further determines whether the received SRS is transmitted from the LTE terminal (step 1002). In case of being transmitted from the LTE terminal, the base station extracts SRS of every LTE UE terminal (step 1003). Specifically, the base station extracts SRS of the UE terminals from the frequency domain, depending on the frequency hopping pattern and other setting information, and then separates SRS multiplexed in the same frequency domain from the code domain, depending on UE specific cyclic shift values.

In case of being not transmitted from the LTE terminal, namely, if it is determined in the step 1002 that SRS is transmitted from the LTE-A terminal, the base station selects a specific component carrier (i.e., chunk) used for SRS transmission, depending on the UE specific SRS transmission setting information and the subframe offset information about component carriers (step 1004). Next, the base station extracts SRS of every LTE-A terminal by performing a frequency domain separation and a code domain separation in each selected component carrier, while depending on the SRS sequence indexes and the cyclic shift values (step 1005). Thereafter, the base station performs a channel estimation from the extracted SRS (step 1006), and then performs a necessary uplink channel control by using the estimated channel values (step 1007).

While this invention has been particularly shown and described with reference to an exemplary embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

A method for transmitting a sounding reference signal (SRS) at a user equipment terminal in an uplink wireless communication system with a multi-carrier transmission scheme, the method comprising:

receiving a subframe offset among component carriers of an uplink channel from a base station;

determining a particular subframe configured for transmission of the SRS in the respective component carriers, depending on the subframe offset;

assigning the SRS to the component carriers corresponding to the particular subframe; and

transmitting the SRS in the particular subframe to the base station.
The method of claim 1, wherein the base station determines the subframe offset such that each of the component carriers transmits the SRS through different subframes if a state value of the uplink channel does not exceed a predetermined value.
The method of claim 1, wherein the base station determines the subframe offset such that at least two of the component carriers transmit the SRS through the same subframe if a state value of the uplink channel exceeds a predetermined value.
The method of claim 1, wherein the subframe offset is for SRS transmission.
A method for receiving a sounding reference signal (SRS) at a base station in an uplink wireless communication system with a multi-carrier transmission scheme, the method comprising:

determining a subframe offset among component carriers of an uplink channel, depending on a state of the uplink channel;

transmitting the subframe offset to a user equipment terminal;

receiving a subframe from the user equipment terminal; and

extracting the SRS from the component carriers corresponding to the received subframe, depending on the subframe offset.
The method of claim 5, wherein the determining of the subframe offset includes determining the subframe offset such that each of the component carriers transmits the SRS through different subframes if a state value of the uplink channel does not exceed a predetermined value.
The method of claim 5, wherein the determining of the subframe offset includes determining the subframe offset such that at least two of the component carriers transmit the SRS through the same subframe if a state value of the uplink channel exceeds a predetermined value.
The method of claim 5, wherein the subframe offset is for SRS transmission.
An apparatus for transmitting a sounding reference signal (SRS) in an uplink wireless communication system with a multi-carrier transmission scheme, the apparatus comprising:

an SRS generator configured to create the SRS by using cyclic shift values assigned from a base station; and

a frequency assignor configured to determine a particular subframe selected for transmission of the SRS in respective component carriers of an uplink channel by depending on a subframe offset among the component carriers, the subframe offset being received from the base station, and configured to assign the SRS to the component carriers corresponding to the particular subframe.
The apparatus of claim 9, wherein the base station is configured to determine the subframe offset such that each of the component carriers transmits the SRS through different subframes if a state value of the uplink channel does not exceed a predetermined value.
The apparatus of claim 9, wherein the base station is configured to determine the subframe offset such that at least two of the component carriers transmit the SRS through the same subframe if a state value of the uplink channel exceeds a predetermined value.
The apparatus of claim 9, wherein the subframe offset is for SRS transmission.
An apparatus for receiving a sounding reference signal (SRS) in an uplink wireless communication system with a multi-carrier transmission scheme, the apparatus comprising:

a means for determining a subframe offset among component carriers of an uplink channel by depending on a state of the uplink channel;

a means for transmitting the subframe offset to a user equipment terminal and for receiving a subframe from the user equipment terminal; and

a means for extracting the SRS from the component carriers corresponding to the received subframe, depending on the subframe offset.
The apparatus of claim 13, wherein the determining means of the subframe offset is configured to determine the subframe offset such that each of the component carriers transmits the SRS through different subframes if a state value of the uplink channel does not exceed a predetermined value.
The apparatus of claim 13, wherein the determining means of the subframe offset is configured to determine the subframe offset such that at least two of the component carriers transmit the SRS through the same subframe if a state value of the uplink channel exceeds a predetermined value.
The apparatus of claim 13, wherein the subframe offset is for SRS transmission.