KR20080056423A - A method of configuring reference signals for cell search - Google Patents

Abstract

A method of configuring reference signals for cell search is provided to increase the number of cells to be identified by utilizing a frequency shift or a frequency hopping. In method of configuring reference signals(601,602,603,604) for cell search, a pseudo-random sequence with a first length is generated. A first sequence is generated by executing a phase rotation on respective elements of the pseudo-random sequence using an orthogonal sequence. The first sequence is mapped on the reference signals. The reference signals are transmitted using plural orthogonal sub-carriers through at least one cell included in one of cell groups that reuse a sequence for the cell search. The cell group includes plural cells corresponding to the sequence for the cell search. Another cell group reuses the sequence for the cell search.

Description

A method of configuring reference signals for cell search

1 and 2 illustrate various methods of including a P-SCH and an S-SCH in a radio frame.

3 is a block diagram illustrating a subframe and a TTI structure for cell search.

4A to 4D are block diagrams showing the configuration of reference symbols used in the present embodiment.

5A to 5D are examples of grouping cells into one group.

6A through 6K are block diagrams illustrating a method of constructing a reference symbol using a sequence of 12 to 48 lengths.

7A to 7C are block diagrams showing frequency shifts according to the second method.

8A to 8B illustrate an example in which a reference symbol is transmitted through the same frequency band in each subframe.

9A to 9C illustrate an example in which reference symbols are transmitted through different frequency bands in each subframe.

10A to 10C illustrate another example in which reference symbols are transmitted through different frequency bands in each subframe.

11 is a diagram illustrating a method for generating an orthogonal sequence using phase rotation according to the present embodiment.

12A is a block diagram illustrating a reference symbol transmitted through one antenna, and FIG. 12B is a block diagram illustrating a reference symbol transmitted through two antennas.

13A-13C are block diagrams illustrating various methods of constructing a reference symbol using a sequence of a specific length.

14 is a block diagram showing another method of configuring a reference symbol when using two transmit antennas.

15A to 15F are block diagrams illustrating an embodiment in which four transmitting antennas are used.

16A through 16C are block diagrams illustrating a method of configuring a reference symbol when using four transmit antennas.

17A to 17D illustrate a method of configuring a reference symbol when four transmission antennas are used.

The present invention relates to cell search in a wireless communication system, and more particularly, to a method of constructing a reference signal for cell search.

Hereinafter, OFDM and OFDMA and SC-FDMA techniques used in the present invention and the prior art will be described.

Recently, the demand for high-speed data transmission is increasing, and OFDM is a suitable method for such a high-speed transmission, and has been recently adopted as a transmission method of various high-speed communication systems. Hereinafter, orthogonal frequency division multiplexing (OFDM) will be described. The basic principle of OFDM is to divide a high-rate data stream into a large number of low-rate data streams, which are transmitted simultaneously using multiple carriers. Each of the plurality of carriers is called a subcarrier. Since orthogonality exists between the multiple carriers of the OFDM, the frequency components of the carriers can be detected at the receiving side even if they overlap each other. The high data rate data stream is converted into a plurality of low data rate data streams through a serial to parallel converter, and each subcarrier is included in the parallel data streams. After multiplying, the respective data strings are summed and sent to the receiving side. OFDMA is a multiple access method for allocating subcarriers according to a transmission rate required by multiple users in the OFD.

Hereinafter, the conventional Single Carrier-FDMA (SC-FDMA) method will be described. The SC-FDMA method is also called a DFT-S-OFDM method. The conventional SC-FDMA technique is a technique mainly applied to uplink. In this scheme, spreading is first applied to a DFT matrix in a frequency domain before generating an OFDM signal, and then the result is modulated by a conventional OFDM scheme and transmitted. . Several variables are defined to describe the SC-FDMA technique. N denotes the number of subcarriers transmitting the OFDM signal, Nb denotes the number of subcarriers for any user, F denotes a discrete Fourier transform matrix, or DFT matrix, s denotes a data symbol vector, x Denotes a vector in which data is distributed in the frequency domain, and y denotes an OFDM symbol vector transmitted in the time domain.

In SC-FDMA, the data symbols s are distributed using a DFT matrix before transmission. This is expressed by the following formula.

는, 데이터 심볼(s)을 분산시키기 위해서 사용된 N_b 크기의 DFT 행렬이다. 이렇게 분산된 벡터(x)에 대하여 일정한 부 반송파 할당 기법에 의해 부 반송파 매핑(subcarrier mapping)이 수행되고, IDFT 모듈에 의해 시간영역으로 변환되어 수신 측으로 전송하고자 하는 신호가 얻어진다. 상기 수신 측으로 전송되는 전송신호는 아래 식과 같다. In Equation 1

It is a DFT matrix of size N _b used to disperse the data symbol (s). Subcarrier mapping is performed on the distributed vector x by a constant subcarrier allocation scheme, and a signal to be transmitted to the receiver is obtained by converting to the time domain by the IDFT module. The transmission signal transmitted to the receiving side is as follows.

는 주파수 영역의 신호를 시간 영역의 신호로 변환하기 위해 사용되는 크기 N의 DFT 행렬이다. 상술한 방법에 의해 생성된 신호 y는, 순환 전치(cyclic prefix)가 삽입되어 전송된다. 상술한 방법에 의해 전송 신호를 생성하여 수신 측으로 전송하는 방법을 SC-FDMA 방법이라 한다. DFT 행렬의 크기는 특정한 목적을 위해 다양하게 제어될 수 있다.In Equation 2

Is a DFT matrix of size N that is used to convert a signal in the frequency domain into a signal in the time domain. The signal y generated by the above-described method is transmitted by inserting a cyclic prefix. The method of generating a transmission signal and transmitting it to the receiving side by the above-described method is called an SC-FDMA method. The size of the DFT matrix can be variously controlled for a specific purpose.

The above description is based on the DFT or IDFT operation. However, for convenience of description, the following description uses a Discrete Fourier Transform (DFT) or Fast Fourier Transform (FFT) operation. If the number of input values of the DFT operation is a power of 2, it will be apparent to those skilled in the art that the FFT operation can be performed instead of the DFT operation. Therefore, the following FFT operation is also applicable to the DFT operation.

Hereinafter, a sequence used in the latest ^{3GPP (3 rd Generation Partnership Project)} (Long Term Evolution) LTE technology newly proposed.

Various sequences are also used in LTE systems. Hereinafter, a sequence used in the channel of LTE will be described.

In general, the first thing the terminal performs to communicate with the base station is to perform synchronization with the base station in a synchronization channel (hereinafter, referred to as 'SCH') and perform a cell search.

A series of processes for synchronizing with a base station and acquiring a cell ID to which a terminal belongs is called a cell search.

The chronization channel (SCH) may have a hierarchical structure. For example, a primary SCH (P-SCH) and a secondary SCH (S-SCH) may be used.

The P-SCH and the S-SCH may be included in a radio frame by various methods.

1 and 2 illustrate various methods of including a P-SCH and an S-SCH in a radio frame. In the LTE system, the SCH may be configured according to the structure of FIG. 1 or 2 according to various situations.

The P-SCH of FIG. 1 is included in the last OFDM symbol of the first subframe. In addition, the S-SCH is included in the last OFDM symbol of the second subframe.

Meanwhile, the P-SCH of FIG. 2 is included in the last OFDM symbol of the first subframe, and the S-SCH is included in the second to second OFDM symbol of the first subframe.

The LTE system may acquire time and frequency synchronization using the P-SCH. In addition, the S-SCH may include a cell group ID, frame synchronization information, antenna configuration information, and the like.

When performing a cell search procedure in the LTE system, a cell ID is obtained using a reference symbol. The reference symbol may be generated using a pseudo-random sequence and an orthogonal sequence together. That is, the reference symbol is composed of a combination of a pseudo noise sequence and an orthogonal sequence.

The reference symbol may be a reference signal or a pilot signal or a pilot symbol or a pilot symbol or a training signal or a training symbol or a pilot. Can be called.

The pseudo noise sequence may be a Walsh code, a gold sequence, a PN sequence, a CAZAC sequence, or the like.

The LTE specification requires that a reference symbol can represent more than 510 cell IDs. In addition, the L1 (Layer 1) cell ID indicated by the reference symbol must have a one-to-one correspondence with a sequence combining a pseudo noise sequence and an orthogonal sequence. [1, 3GPP, R1-063008, Ericsson, "Downlink reference signals"]

In performing the cell search procedure, the cell ID is obtained by a reference symbol transmitted through the middle band 1.25 MHz (or 1.08 Mhz) of the transmission band.

3 is a block diagram illustrating a subframe and a TTI structure for cell search.

As shown, the left side of FIG. 3 is an example in which one subframe consists of seven OFDM symbols. An OFDM symbol represents a set of OFDM samples transmitted simultaneously for one unit time by an IFFT or IDFT operation.

The OFDM symbol 1 and the OFDM symbol 5 of the 7 OFDM symbols may include a reference symbol, the OFDM symbol 6 may include an S-SCH, and the OFDM symbol 7 may include a P-SCH. In this case, a cell ID may be obtained using only one reference symbol (for example, symbol 5) in one subframe, and two reference symbols (for example, symbol 1 and symbol 5) It is also possible to obtain a cell ID using. Coherent detection is advantageous when only a reference symbol (for example, symbol 5) adjacent to the S-SCH is used.

As shown, the right side of FIG. 3 is an example in which 14 OFDM symbols are transmitted during one TTI. In this case, a cell ID may be found using reference symbols 1 and 5 of the first subframe and reference symbols 1 and 5 of the second subframe. That is, the cell ID can be found using four reference symbols. In addition, the cell ID may be found using the reference symbol 5 of the first subframe and the reference symbol 1 of the second subframe. In addition, the cell ID may be found using only the 5th reference symbol of the first subframe. Coherent detection is possible when using only reference symbols adjacent to the S-SCH (for example, reference symbol 5 of the first subframe or reference symbol 5 of the first subframe and reference symbol 1 of the second subframe). There is this.

In summary, a cell ID may be found using at least one reference symbol among four reference symbols included in one subframe or two subframes transmitted during one TTI. In particular, the cell ID may be found using only one or two reference symbols adjacent to the S-SCH for coherent detection.

The problems of the prior art will be described below.

When performing a cell search, the reference symbol transmitted through the middle band 1.25 MHz (or 1.08 MHz) should include information for distinguishing more than 510 cells.

In the case of using a structure of a radio block of the conventional LTE standard, when reference signals are arranged at intervals of six subcarriers in a 1.25 MHz band, one OFDM symbol includes 12 reference symbols. That is, a sequence of length 12 is used to construct a reference symbol for obtaining a cell ID in one OFDM symbol.

If a cell ID is found during one subframe according to the conventional LTE standard, the cell ID is found according to the contents shown on the left side of FIG. That is, two of the OFDM symbols transmitted for 0.5 ms include a reference symbol. In this case, one OFDM symbol includes a sequence of length 12, so two OFDM symbols include a sequence of length 24. In this case, two OFDM symbols may include only 24 kinds of pseudo noise sequences in total.

Meanwhile, if a cell ID is found for two subframes (ie, for one TTI) according to the conventional LTE standard, the cell ID is found according to the contents shown on the right side of FIG. 3. That is, four of the OFDM symbols transmitted for 1 ms include a reference symbol. In this case, since one OFDM symbol includes a sequence of length 12, four OFDM symbols include a sequence of length 48. In this case, four OFDM symbols may include only 48 kinds of pseudo noise sequences in total.

As described above, the reference symbol should distinguish at least 510 cells, but the reference symbol according to the prior art does not distinguish a large number of cells.

The present invention has been proposed to solve the above-mentioned problems of the prior art, and an object of the present invention is to propose a method of designing a reference symbol for distinguishing a large number of cells.

Another object of the present invention is to propose a method of designing a reference symbol representing various information required for communication.

Summary of the Invention

The present invention to achieve the above object, generating a pseudo noise sequence of a first length; Using an orthogonal sequence, performing phase rotation on each component of the pseudo noise sequence to generate a first sequence; Mapping the first sequence to a reference signal; The reference signal is transmitted through at least one cell included in at least one cell group among cell groups reusing a sequence for discovery, and the reference signal is transmitted using a plurality of orthogonal subcarriers. And transmitting, wherein the cell group includes a plurality of cells corresponding to the type of the sequence for the cell search, and different cell groups reuse the sequence for the cell search.

The present invention also provides a method of generating a pseudo noise sequence of a first length; Using an orthogonal sequence, performing phase rotation on each component of the pseudo noise sequence to generate a first sequence; Mapping the first sequence to a reference signal by performing a frequency shift according to control information to be transmitted through the first sequence; And transmitting the reference signal using a plurality of orthogonal subcarriers.

One embodiment of the invention

This embodiment proposes a method of configuring a reference symbol for cell search. The present invention proposes to construct a reference symbol according to the following five methods.

The first method relates to increasing the number of distinguishable cells by reusing sequences through cell grouping.

The second method relates to increasing the number of distinguishable cells using frequency shift or frequency hopping.

The third method is to use the first method and the second method together.

The fourth method relates to maintaining orthogonality between cells by performing phase rotation on a reference symbol.

The fifth method relates to constructing a reference symbol in MISO (Multiple Input and Single Output) or MIMO (Multiple Input and Multiple Output).

One of the five methods described above may be used or at least two methods may be used at the same time.

In applying the present embodiment, there is no limitation on the type of sequence included in the reference symbol. In addition, there is no limitation on the spacing between reference symbols.

4A to 4D are block diagrams showing the configuration of reference symbols used in the present embodiment. The patterns of FIGS. 4A-4D may vary for each subframe or for each TTI.

As shown, a subframe transmitted for 0.5 ms consists of seven OFDM symbols. Each OFDM symbol also consists of a plurality of samples.

For example, referring to the first OFDM symbol of FIG. 4A, a sample mapped to a subcarrier corresponding to the first frequency index includes a 'R ₁ ' symbol. In addition, arbitrary data 'D' is included in the second to sixth samples. The seventh sample includes the 'R ₁ ' symbol again, and the random data 'D' is included in the eighth to twelfth samples. Only the arbitrary data 'D' is included in the second to fourth OFDM symbols, and the 'R ₂ ' symbol is included in the fifth OFDM symbol. Each reference symbol (R ₁ , R ₂ symbol) is arranged at six frequency index intervals.

According to the LTE standard, the number of reference symbols for obtaining a cell ID included in one OFDM symbol is 12. That is, all 12 reference symbols are indicated by the leader line 401. In addition, all the reference symbols indicated by the leader line 402 are also twelve. Therefore, by constructing a reference symbol using a pseudo noise sequence, twelve cells can be identified.

4B to 4C illustrate an example of identifying a cell using all reference symbols included in one subframe. That is, 24 reference symbols are constructed using a pseudo noise sequence of 24 lengths.

If there are 24 pseudo noise sequences (c ₀ , c ₁ ,..., C ₂₃ ), the method of mapping 24 components to 24 reference symbols may vary. 4B illustrates a method of corresponding c ₀ to the first reference symbol of the first OFDM symbol and c ₁ to the first reference symbol of the fifth OFDM symbol.

4C and 4D show another method of generating all reference symbols included in one subframe using one pseudo noise sequence.

4B to 4D, reference symbols may be generated using a sequence having a long length. In general, the longer the pseudo noise sequence, the more kinds of information can be represented. Therefore, it is preferable to use the method shown in Figs. 4B to 4D so that a long pseudo noise sequence can be used.

4B to 4D are only examples of the present invention, and the present invention is not limited thereto.

First way

The first method relates to sequence reuse through cell grouping. The first method proposes to group a plurality of cells into one group and to use different reference signals in the same group, but different groups reuse the already used reference signals.

5A illustrates an example in which 21 cells are grouped into one group. For convenience of explanation, assume that each cell is a hexagonal grid.

That is, 21 cells are included in 501 and 502 groups. For example, if 21 sequences (s ₀ , s ₁ to s ₂₀ ) capable of identifying 21 cells are prepared, 21 cells belonging to the 501 group form a reference symbol using s ₀ to s ₂₀ sequences. In this case, 21 cells belonging to the 502 group form a reference symbol by reusing the s ₀ to s ₂₀ sequences.

Since the groups are separated by distance, the sequence can be reused without using a separate technique to distinguish each group. By grouping cells and reusing sequences in each cell, you can identify the desired number of cells.

Hereinafter, it is an example for explaining the number of cells that can be distinguished according to the first method.

Example 1.1.1.1

When using a pseudo-noise sequence having a length of 12, a pseudo-random sequence (hereinafter referred to as 'PRS') as long as the sequence length can be generated. That is, the maximum number of information (hereinafter, referred to as 'N _PRS ') represented by the pseudo noise sequence is '12'. In this case, it is assumed that the number of information (hereinafter, referred to as 'N _OS ') that can be represented by an orthogonal sequence (hereinafter, referred to as 'OS') is '3'. Then, the number of identifiable cells (hereinafter, referred to as 'N _cell ') becomes '36' (= 12 * 3). N _cell is determined by the product of N _PRS and N _OS .

In this case, it is preferable to group 36 cells into one group. That is, it is preferable to distinguish the cells by reusing a sequence (that is, a combination of PRS and OS) constituting a reference symbol for each 36 cells or less.

There is no limitation on how to generate a PRS of length 12. For example, a PAZ having a length of 12 may be generated by generating a CAZAC sequence having a length of 13 or more and removing some components therefrom.

Example 1.1.1.2

Using CAZAC sequence among various PRS is as follows. When using a CAZAC sequence having a length of 12, N _PRS becomes '4' due to the characteristics of the CAZAC sequence. The reason why N _PRS is '4' even though the length is '12' is because when the variable n is input to a generation formula for generating a CAZAC sequence, the CAZAC sequence is generated by the number of natural numbers less than n among the natural numbers smaller than n. to be.

In this case, when N _OS is '3', N _cell is '12'. Therefore, it is preferable to distinguish the cells by reusing a sequence constituting a reference symbol (that is, a combination of PRS and OS) for every 12 cells or less.

Example 1.1.1.3

Decimal using a CAZAC sequence of length 11 (Prime number) it can be assumed that as the NPRS = 10, and N _OS '3'.

In this case, N _cell is '30'. Therefore, it is desirable to distinguish the cells by reusing a sequence constituting a reference symbol (that is, a combination of PRS and OS) for every 30 cells or less. In this case, '0' is inserted, '1' is inserted or a random sequence is inserted in the 30th last pilot position.

Example 1.1.1.4

After generating a CAZAC sequence of length 13 with a prime number, one component is removed and a sequence of length 12 is used, resulting in N _PRS = 12.

In this case, when N _OS is '3', N _cell is '36'. Therefore, it is desirable to distinguish the cells by reusing a sequence constituting a reference symbol (that is, a combination of the PRS and the OS) every 36 cells or less.

As described above, examples of 1.1.1.1 to 1.1.1.4 are examples of generating one reference symbol through a sequence of length 12 according to FIG. 4A. Using the example of FIGS. 4B-4D, one reference symbol may be generated through a sequence of length 24. Hereinafter, an example of using a sequence of length 24 will be described.

Example 1.1.2.1

If you use a sequence of length 24, you can create a PRS as long as the sequence. Therefore, since N _PRS is '24', when N _OS is '3', N _CELL is '72'. Therefore, it is desirable to distinguish the cells by reusing a sequence constituting a reference symbol (that is, a combination of PRS and OS) for every 72 cells or less.

Example 1.1.2.2

Using a 24 length CAZAC sequence, eight PRSs can be created. Since N _PRS is '8', when N _OS is '3', N _CELL is '24'. Therefore, it is desirable to distinguish cells by reusing a sequence constituting a reference symbol (that is, a combination of PRS and OS) for every 24 cells or less.

Example 1.1.2.3

Using a sequence of length 22 that produces a prime number 23 CAZAC sequence yields N _PRS = 22.

In this case, when N _OS is '3', N _cell is '66'. Therefore, it is desirable to classify cells by reusing a sequence constituting a reference symbol (ie, a sequence combining PRS and OS) for every 66 cells or less. At this time, '0', '1' or random sequence is inserted into the 24th last pilot position.

Example 1.1.2.4

After generating a CAZAC sequence of length 29 with a prime number, removing the components and using the sequence of length 24 results in N _PRS = 28. In this case, when N _OS is '3', N _cell is '84'. Therefore, it is preferable to distinguish the cells by reusing a sequence constituting a reference symbol (that is, a combination of the PRS and the OS) for every 84 cells or less.

5B is a block diagram showing 57 cells in one group. 5C is a block diagram showing 111 cells in one group. 5D is a block diagram showing 183 cells in one group. 5E is a block diagram showing 273 cells in one group.

Therefore, using the structure of FIG. 5B, a sequence (that is, a combination of PRS and OS) constituting a reference symbol may be reused for every 57 cells, and 111 sequences may be reused using the structure of FIG. 5C. In FIG. 5D, 183 sequences may be reused, and in FIG. 5E, 273 sequences may be reused.

For example, according to the example of 1.1.2.4, PRS should be reused for every 84 cells or less. Therefore, the example of FIG. 5A or 5B can be used.

In the first method, each group generated by grouping cells may be distinguished by scrambling. That is, the first group may be assigned a scrambling code of a specific first scheme, and the second group may be assigned a scrambling code of a specific second scheme to distinguish each group.

6A through 6K are block diagrams illustrating a method of constructing a reference symbol using a sequence of 12 to 48 lengths. The patterns of FIGS. 6A-6K may vary for each subframe or for each TTI.

When a cell search is performed during one TTI and a reference symbol is inserted at six frequency index intervals, the reference symbol may be configured according to the method of FIGS. 6A to 6K.

In the case of FIG. 6A, up to four sequences having a length of 12 (a sequence generated with a length of 12 from the beginning or a sequence in which 13 or more sequences are removed to remove some components) may be used. That is, twelve reference symbols indicated by the leader line 601 may be configured using the first sequence of length 12 (a sequence generated by the combination of the PRS and the OS), and the leader line 602 using the second sequence of length 12. Twelve reference symbols indicated by. In addition, twelve reference symbols indicated by the leader lines 603 and 604 may be configured using the third and fourth sequences having a length of 12, respectively.

In the case of FIG. 6B, 24 reference symbols represented by the leader lines 611 and 612 are constructed using a sequence of length 24 (a sequence generated from the beginning 24 or a sequence having 25 or more sequences and some components removed). can do.

FIG. 6C is a method of constructing a sequence having the same length as that of FIG. 6B, but using a modified method.

FIG. 6D may configure 48 reference symbols indicated by the leader line 630 using a sequence of length 48 (a sequence generated with a length of 48 from the beginning or a sequence in which 49 or more sequences are removed to remove some components).

Various methods are possible in addition to the method of FIG. 6D, and FIGS. 6E-6K are examples of such various methods.

The examples of 1.1.1.1 to 1.1.2.4 described above can be applied to the examples of FIGS. 6A to 6C as they are.

Hereinafter, a method applicable to the example of FIGS. 6D to 6K will be described. The example described below is basically based on the example of 1.1.1.1-1.1.2.4 mentioned above, and only a specific numerical value differs.

Example 1.2.3.1

In the case of using a sequence of length 36, a PRS as long as the sequence length can be made. In this case, if N _OS = 3, N _PRS = 36, so N _cell = 108. Therefore, it is preferable to distinguish the cells by reusing a sequence constituting a reference symbol (that is, a combination of PRS and OS) for every 108 cells or less.

Example 1.2.3.2

Using a CAZAC sequence of length 36 and assuming N _OS = 3, N _PRS = 12 and N _cell = 36. Therefore, it is desirable to distinguish the cells by reusing a sequence constituting a reference symbol (that is, a combination of the PRS and the OS) every 36 cells or less.

Example 1.2.3.3

If a CAZAC sequence having a length of prime number 31 is used and N _OS = 3, N _PRS = 31 and N _cell = 93. Therefore, it is desirable to distinguish the cells by reusing a sequence constituting a reference symbol (that is, a combination of the PRS and the OS) every 36 cells or less. Insert a '0' or insert a '1' or a random sequence at the position of the last pilot that is insufficient because the generated sequence is short in length.

Example 1.2.3.4

A prime number 37 length CAZAC sequence was generated to remove some components, followed by a 24 length sequence, and if N _OS = 3, then N _PRS = 36. That is, N _cell = 108. Therefore, it is preferable to distinguish the cells by reusing a sequence constituting a reference symbol (that is, a combination of PRS and OS) for every 108 cells or less.

Hereinafter, examples of 1.2.4.1 to 1.2.4.4 relate to a method of constructing 48 reference signals transmitted during one TTI.

Example 1.2.4.1

If a sequence of length 48 is used, PRS can be made as long as the sequence length. If N _OS = 3, N _PRS = 48. Therefore, since N _cell = 144, it is preferable to distinguish cells by reusing a sequence (that is, a combination of PRSs and OSs) constituting a reference symbol for every 144 cells or less.

Example 1.2.4.2

When using a CAZAC sequence of length 48, assuming N _OS = 3, N _PRS = 16. In addition, since N _cell = 48, it is preferable to distinguish cells by reusing a sequence (that is, a combination of PRS and OS) constituting a reference symbol for every 48 cells or less.

Example 1.2.4.3

Assuming 47 prime length CAZAC sequences and N _OS = 3, N _PRS = 46 and N _cell = 138. In such a case, it is desirable to distinguish the cells by reusing a sequence constituting a reference symbol (that is, a combination of the PRS and the OS) for each of 138 or less cells. In this case, '0' is inserted, '1' is inserted or a random sequence is used at the position of the pilot shortened due to the short length of the generated sequence.

Example 1.2.4.4

When a 53-length CAZAC sequence is generated by removing a few components, a 48-length sequence is used after removing some components, and if N _OS = 3, N _PRS = 52 and N _cell = 156. In such a case, it is preferable to distinguish cells by reusing a sequence constituting a reference symbol (that is, a sequence combining PRS and OS) for every 156 or less cells.

As described above, each group grouped by the present embodiment may be divided by a scrambling technique.

Second way

The second method relates to a method of displaying more information using frequency shift. The frequency shift is a technique of sending different frequency domains in which a reference symbol is transmitted for a subframe or TTI. The frequency shift may be referred to as frequency hopping.

7A to 7C are block diagrams showing frequency shifts according to the second method. In the case of FIG. 7A, the frequency domain in which the 701 or 702 reference symbol is transmitted is as shown. Meanwhile, the frequency domain in which the reference symbols are transmitted in FIG. 7A is different from the frequency domain in which the reference symbols 711 and 712 are transmitted in FIG. 7B. That is, in FIG. 7B, frequency shift or frequency hopping is performed according to a preset rule.

7A, 7B, and 7C, it can be seen that the frequency domains in which the reference symbols are transmitted are different from each other. Since the cell IDs can be distinguished through different frequency domains, six additional pieces of information can be represented.

In FIG. 7A to FIG. 7C, the time-frequency domain in which the reference symbol is transmitted may be different for each cell or for each base station (Node B). In addition, even in the same cell or the same base station (Node B) may be different for each subframe.

Hereinafter, for convenience of explanation, it is assumed that the start position of the pilot is the 0 th subcarrier and there is no change in the subframe.

An example of using the sequence of length 12 or the sequence of length 24 as in the example of FIGS. 4A to 4D described above will be described. Since the second method of this embodiment uses frequency shift, the following example relates to a method of identifying cell ID according to the frequency shift.

Example 2.1.1.1

In case of using a sequence of length 12, PRS as long as the length of the sequence can be made, and if N _OS = 3, N _PRS = 12. In this case, six types of information may be additionally classified according to the frequency shifting technique. When the number of additionally distinguishable information according to the frequency shifting technique is called 'N _shift ', N _cell = N _OS * N _PRS * N _shift = 216. Of course, 510 cells cannot be identified, but the first method can be used together to reuse the sequence in units of 216 cells.

Example 2.1.1.2

When using a length 12 CAZAC sequence, assuming N _OS = 3, N _PRS = 4 and N _shift = 6. Therefore, N _cell = 72. Although up to 72 cells can be distinguished, 510 cells cannot be distinguished. In this case, the first method can be used together to reuse the sequence in 72 cell units.

Example 2.1.1.3

If a small 11 length CAZAC sequence is used and N _OS = 3, then N _PRS = 10. Therefore, N _cell = 180. That is, up to 180 cells can be distinguished. Of course, 510 cells cannot be identified, but the first method can be used together to reuse the sequence in units of 180 cells.

Example 2.1.1.4

After generating a fractional 13-length CAZAC sequence to remove some components, using a 48-length sequence and N _OS = 3, N _PRS = 12. In this case, since N _cell = 216, it is possible to distinguish a maximum of 216 cells. Of course, 510 cells cannot be identified, but the first method can be used together to reuse the sequence in units of 216 cells.

Example 2.1.2.1

In case of using a sequence of length 24, PRS as long as the length of the sequence can be made, and assuming that N _OS = 3, N _PRS = 24. Therefore, N _cell = 432. Of course, 510 cells are not identified, but the first method can be used together to reuse the sequence in units of 432 cells.

Example 2.1.2.2

When using a CAZAC sequence of length 24, assuming N _OS = 3, N _PRS = 8. Therefore, since N _cell = 144, 144 cells can be distinguished. Of course, 510 cells cannot be identified, but the first method can be used together to reuse the sequence in units of 144 cells.

Example 2.1.2.3

If a small 23-length CAZAC sequence is used and N _OS = 3, N _cell = 396 when N _PRS = 22. That is, up to 396 cells can be distinguished. In this case, of course, 510 cells cannot be identified, but the first method can be used together to reuse the sequence in units of 396 cells.

Example 2.1.2.4

If a small 29-length CAZAC sequence is generated to remove some components and a 28-length sequence is used, and N _OS = 3, N _PRS = 28, so N _cell = 504. In this case, of course, 510 cells are not identified, but the first method can be used together to reuse the sequence in units of 504 cells.

8A to 8B illustrate an example in which a reference symbol is transmitted through the same frequency band in each subframe. That is, the 801 reference symbol and the 802 reference symbol of FIG. 8A are transmitted by the same subcarrier, and the 811 reference symbol of FIG. 8B is transmitted by the same subcarrier as the 812 reference symbol.

In FIG. 8A and FIG. 8B, since the frequency domain in which the reference symbols are transmitted are different, they may represent different cell IDs.

9A to 9C illustrate an example in which reference symbols are transmitted through different frequency bands in each subframe. That is, reference symbols 901 and 911 of FIG. 9A are transmitted through different subcarriers, and reference symbols 921 and 222 of FIG. 9B are transmitted through different subcarriers. Also, reference symbols 931 and 932 of FIG. 9C are transmitted through different subcarriers.

9A to 9C may be used as information representing specific cell IDs, respectively.

10A to 10C illustrate another example in which reference symbols are transmitted through different frequency bands in each subframe. As shown, reference symbols may be transmitted through various frequency rentals.

An example of performing cell search during one TTI may be based on FIGS. 8 to 10. That is, the position of the reference symbol within one TTI may be according to FIGS. 8 to 10. According to the example of FIGS. 8 to 10, reference symbols may be constructed using sequences of 12, 24, 36, and 48 lengths.

When the length is 12 or 24, the description is the same as in Examples 2.1.1.1 to 2.1.1.4 described above, and thus description thereof is omitted.

Hereinafter, a method of constructing a reference symbol using a sequence of length 36 or more will be described.

Example 2.1.3.1

In the case of using a sequence of length 36, a PRS corresponding to the length of the sequence can be made, and assuming that N _OS = 3, N _PRS = 36. In this case, since N _shift = 6, N _cell = 3 * 36 * 6 = 648 cells can be distinguished. That is, the number of cells required by the LTE standard can be distinguished.

Example 2.1.3.2

When using a CAZAC sequence of length 36, assuming N _OS = 3, N _PRS = 12. Therefore, N _cell = 3 * 12 * N _sfhit = 216. That is, up to 216 cells can be distinguished. In this case, the basic number of cells, 510, is not satisfied. In this case, the first method can be used together to increase the number of distinguishable cells.

Example 2.1.3.3

Using a 31-length CAZAC sequence with a prime number and assuming N _OS = 3, N _PRS = 30. In this case, Ncell = 3 * 30 * N _shift = 540. That is, cells required by the LTE standard can be distinguished. In this case, since the generated sequence has a short length, the last pilot position that is insufficient is inserted by inserting '0', inserting '1', or inserting a random sequence.

Example 2.1.3.4

If you create a 37-length CAZAC sequence with a small number, remove some components, and then use a 48-length sequence and assume that N _OS = 3, then N _PRS = 36. N _cell = 3 * 36 * N _shift = 648. That is, the number of cells required by the LTE standard can be distinguished.

Example 2.1.4.1

If a sequence of length 48 is used, PRS can be made as long as the sequence length, and assuming that N _OS = 3, N _PRS = 48. N _cell = 3 * 48 * N _shift = 864. That is, the number of cells required by the LTE standard can be distinguished.

Example 2.1.4.2

When using a CAZAC sequence of length 48, N _PRS = 16, assuming N _OS = 3. N _cell = 3 * 16 * N _shift = 288.

Example 2.1.4.3

Using a 47-length CAZAC sequence with a prime number, assuming N _OS = 3, N _PRS = 46. In this case, Ncell = 3 * 46 * N _shift = 828. That is, cells required by the LTE standard can be distinguished. In this case, since the generated sequence has a short length, the last pilot position that is insufficient is inserted by inserting '0', inserting '1', or inserting a random sequence.

Example 2.1.4.4

If we create a 53-length CAZAC sequence that is a prime number, remove some components, use a 48-length sequence, and assume that N _OS = 3, then Ncell = 3 * 52 * N _shift = 936. That is, cells required by the LTE standard can be distinguished.

When the cell ID is identified through the frequency shift as described above, information on how the frequency shift is performed may be known through the Node B ID or the cell group ID.

For example, through grouping for Node B, Node B ID or cell group ID 1 to 144 should be used from the first subcarrier, ID 145 to 288 from the second subcarrier, and ID 289 to 432 for the third subcarrier. From the carrier, ID 433 to 576 can be used from the fourth subcarrier, ID 577 to 750 from the fifth subcarrier, and ID 751 to 864 from the sixth subcarrier.

Since the Node B ID or the cell group ID can be obtained in advance through the S-SCH, the receiving end can know which subcarrier includes the reference symbol by the above-described method. Using the above method, there is an advantage that does not increase the complexity and overhead that occurs during cell search. As such, when frequency shift is performed on the reference symbol, pilot power boosting may be performed to improve power of the reference symbol.

Third way

The first method and the second method described above are used in combination. Even if the second method cannot distinguish 510 cells, the first method can be used together to adjust the number of distinguishable cells.

Fourth way

Hereinafter, a method of indicating cell ID information using an orthogonal sequence for reference symbols used in the present embodiment will be described.

When the phase rotation is performed according to the fourth method, the receiving end may acquire information according to the phase rotation because of orthogonality caused by the phase rotation.

Reference symbols transmitted over a 1.25 MHz band for cell search may generate three or six orthogonal sequences (OSs) as follows according to phase rotation.

The case where N _OS = 3 is described below.

11 is a diagram illustrating a method for generating an orthogonal sequence using phase rotation according to the present embodiment.

In FIG. 11, phase rotation is performed in the time domain and the frequency domain, respectively. In FIG. 11, phase rotation by 'θ' is performed between the 1101 reference sample and the 1103 reference sample. Phase rotation is performed in the frequency domain between the 1101 reference sample and the 1103 reference sample. In addition, a phase rotation of 'Φ' is performed between the 1101 reference sample and the 1102 reference sample. Phase rotation is performed in the time domain between the 1101 reference sample and the 1102 reference sample.

More specifically, 'θ' and 'Φ' are preferably determined by the following equation.

For example, in the case of indicating information of a specific sector 1 or cell 1, 'θ' and 'Φ' are set to '0'. That is, phase rotation of '0' degrees is performed between the 1101 reference sample and the 1103 reference sample, and phase rotation of '0' degrees is also performed between the 1101 reference sample and the 1102 reference sample. As a result, phase rotation of '0' degrees is performed between the reference samples included in one subframe.

If information indicating that the first sector or the first cell is information, 'θ' and 'Φ' are defined as '2π / 3' and '4π / 3'. That is, phase rotation by 2π / 3 is performed between the 1101 reference sample and the 1103 reference sample. In addition, phase rotation of 'θ' is performed again between the reference sample located on the right side of the 1103 reference sample and the 1103 reference sample. That is, phase rotation by 2π / 3 is performed, and phase rotation by 'θ' is continuously performed in the right direction. In addition, a phase rotation of 4π / 3 is performed between the 1101 reference sample and the 1102 reference sample. In addition, a phase rotation of 'θ' is performed between the 1102 reference sample and the sample positioned to the right of the 1102 reference sample. That is, phase rotation by 2π / 3 is performed, and phase rotation by 'θ' is continuously performed in the right direction.

If information indicating that the second sector or the second cell is specific, 'θ' and 'Φ' are determined as '4π / 3' and '2π / 3'. That is, phase rotation by 4π / 3 is performed between the 1101 reference sample and the 1103 reference sample. In addition, phase rotation of 'θ' is performed again between the reference sample located on the right side of the 1103 reference sample and the 1103 reference sample. That is, phase rotation by 4π / 3 is performed, and phase rotation by 'θ' is continuously performed in the right direction. In addition, a phase rotation of 2π / 3 is performed between the 1101 reference sample and the 1102 reference sample. In addition, a phase rotation of 'θ' is performed between the 1102 reference sample and the sample positioned to the right of the 1102 reference sample. That is, phase rotation by 4π / 3 is performed, and phase rotation by 'θ' is continuously performed in the right direction.

When the phase shift is performed according to Equation 3, the transmitter can additionally transmit three types of information. In addition, when the receiving end obtains a sum by rotating in the opposite direction to Equation 3 with respect to the received sequence, the receiving end can know which of the three types of information corresponds to the information transmitted from the transmitting end.

In the same way as above, N _OS = 3 can be set.

The case where N _OS = 6 is described below.

Six pieces of information may be represented by the following equation (4) or (5). Equation 4 displays six pieces of information by reusing a phase rotation value, and Equation 5 displays six pieces of information by determining six types of phase rotation values.

Fifth way

The fifth method relates to a method applied to an MISO or MIMO system. When using multiple transmit antennas, the particular first transmit antenna uses the first to fourth methods described above, and the particular second transmit antenna also uses the first to fourth methods described above. In this case, the method used by the first transmit antenna and the method used by the second transmit antenna may be the same or different from each other.

12A is a block diagram illustrating a reference symbol transmitted through one antenna, and FIG. 12B is a block diagram illustrating a reference symbol transmitted through two antennas.

In the case of MISO or MIMO, the reference symbol transmitted through any one of the plurality of antennas is preferably transmitted through the same frequency-time as the reference symbol transmitted in the SISO. In the case of MISO or MIMO, since the structure of the SISO is used, an increase in overhead and complexity can be avoided.

The frequency-time resource of the reference symbols transmitted through the first transmit antenna Tx 1 in FIG. 12B is the same as the frequency-time resource of the reference symbols transmitted in FIG. 12A. Therefore, regardless of whether the receiver supports the MIMO mode, the cell ID may be found using only the reference symbols of the first transmission antenna during cell search. In addition, if the receiving end knows whether the MIMO mode is present, the RS of the second antenna may be additionally used for cell search.

As described above, the first transmission antenna may use any one of the examples of FIGS. 4 and 6, and the second transmission antenna Tx 2 may use any one of the examples of FIGS. 4 and 6.

Each transmit antenna is created by a sequence of the same or different lengths. That is, the first transmit antenna may be generated by a pseudo orthogonal sequence of length 12 and the second transmit antenna may be generated by a pseudo orthogonal sequence of length 24.

Furthermore, which sequence is mapped to which reference symbol is determined equally or differently for each transmit antenna.

In addition, the above-described phase rotation (rotation by OS) is also performed to each transmission antenna equally or differently.

13A-13C are block diagrams illustrating various methods of constructing a reference symbol using a sequence of a specific length.

Referring to FIG. 13A, the reference symbol indicated by the leader line 1301 is for the first transmit antenna, and the reference symbol indicated by the leader line 1302 is for the second transmit antenna. The length of the sequence used for the reference symbol indicated by 1301 and the length of the sequence used for the reference symbol indicated by 1302 are the same. In addition, the correspondence between each component of the sequence and the reference symbol is equally applied to the first transmission antenna and the second transmission antenna.

13B, the reference symbol indicated by the leader line 1311 is for the first transmit antenna, and the reference symbol indicated by the leader line 1312 is for the second transmit antenna. The length of the sequence used for the reference symbol indicated by 1311 and the length of the sequence used for the reference symbol indicated by 1312 are the same. However, the correspondence between each component of the sequence and the reference symbol is applied differently to the first transmit antenna and the second transmit antenna.

Referring to FIG. 13C, the reference symbol indicated by the leader line 1323 is for the first transmit antenna, and the reference symbol indicated by the leader lines 1321 and 1322 is for the second transmit antenna. The length of the sequence used for the reference symbol indicated by 1323 and the length of the sequence used for the reference symbol indicated by 1321 or 1322 are different from each other. Also, the correspondence between each component of the sequence and the reference symbol is applied differently to the first transmit antenna and the second transmit antenna.

14 is a block diagram showing another method of configuring a reference symbol when using two transmit antennas. For example, when the reference symbol of the first transmit antenna is used for cell search, the reference symbol of the second transmit antenna is generated only within a specific frequency band (for example, 1.25 Mhz or 1.08 Mhz) for cell search, or the entirety. Can be created in the system band.

Referring to FIG. 14, reference symbols displayed on the 1401, 1402, 1406 leader lines, and the like are not limited to a specific band (BW for cell search) but are generated over the entire system band. That is, reference symbols transmitted from the second transmit antenna may be generated over the entire system band.

Even when the reference symbol of each transmit antenna is generated in the entire system band, mapping methods such as FIGS. 4 and 6 may be used in combination.

15A to 15F are block diagrams illustrating an embodiment in which four transmitting antennas are used. Indicated. 15A to 15F, all reference symbols transmitted by the first transmit antenna Tx 1 are transmitted on the same frequency-time resource. Therefore, regardless of the MIMO mode, the cell search may be performed using only the reference symbol of the first transmit antenna during cell search. If the MIMO mode is known, the RS of another antenna may be additionally used for cell search.

The method of configuring a reference symbol for each transmission antenna may be based on the example of FIGS. 4 and 6. In this case, as described above, the length of a sequence and a method of constructing a sequence may be differently applied to each transmit antenna. In addition, phase rotation according to the OS may be applied to each transmitting antenna.

16A through 16C are block diagrams illustrating a method of configuring a reference symbol when using four transmit antennas.

In the case of FIG. 16A, a leader line 1601 indicates a reference symbol transmitted through a first transmit antenna, a leader line 1602 indicates a reference symbol transmitted through a second transmit antenna, and a leader line 1603 indicates a reference symbol transmitted through a third transmit antenna. Leader 1604 indicates a reference symbol transmitted through the fourth transmit antenna. As shown, the reference symbols transmitted through the four antennas are generated by a sequence of equal lengths to each other, and the method in which each reference symbol is configured is equally applied to all antennas.

In the case of FIG. 16B, reference symbols transmitted through four antennas are generated by sequences having the same length. However, the method of configuring the reference symbols of the first and second transmission antennas and the method of configuring the reference symbols of the third and fourth transmission antennas are different from each other.

In the case of FIG. 16C, reference symbols of the first and second transmission antennas and reference symbols of the third and fourth transmission antennas are generated by sequences having different lengths. In addition, the method of configuring the reference symbols of the first and second transmission antennas and the method of configuring the reference symbols of the third and fourth transmission antennas are different from each other.

17A to 17D illustrate a method of configuring a reference symbol when four transmission antennas are used.

If only the reference symbol of the nth transmit antenna is used for cell search, the reference symbol of the other transmit antenna is generated within the band for the cell search (for example, 1.25MHz or 1.08Mhz) and the entire system band Consideration can be given to cases made within.

Even when the reference symbols of the individual transmit antennas are configured in the entire system band, configuration methods such as FIGS. 4 and 6 may be used in combination.

In the case of FIG. 17A, a reference symbol of the first transmit antenna indicated by the 1704 leader line is generated within a band (eg, 1.25 MHz or 1.08 Mhz) for cell search. Meanwhile, reference symbols of the remaining transmit antennas indicated by the 1701, 1702, and 1703 leader lines are configured in the entire system band. In addition, the reference symbol of each transmit antenna is configured by various methods.

In the case of FIG. 17B, a reference symbol of the first transmit antenna indicated by the 1714 leader line is generated in a band for cell search. Meanwhile, reference symbols of the remaining transmit antennas indicated by the 1711, 1712, and 1713 leader lines are configured in the entire system band. In addition, the reference symbol of each transmission antenna is constructed by various methods different from the example of FIG. 17A.

In the case of FIG. 17C, a reference symbol of the first transmit antenna indicated by the 1724 leader is made in band for cell search. In addition, the reference symbol of each transmission antenna is comprised by various methods different from the example of FIG. 17A, 17B.

In the case of FIG. 17D, a reference symbol of the first transmit antenna indicated by the 1734 leader line is generated in a band for cell search. In addition, the reference symbol of each transmission antenna is comprised by various methods different from an example of FIG. 17A, 17B, 17C.

In the case of a multiple transmit antenna system, compared to a single transmit antenna system, the position and length of a reference symbol within a cell search band of a specific antenna do not change. In addition, cell searching can be performed using reference symbols without increasing any overhead and complexity.

In the case of cell searching using only one particular antenna, there is no change in the method and number of sequence reuse, which is the first method described above. However, a difference occurs when cell IDs are distinguished by frequency shift. If one transmit antenna is used, six frequency separations are possible, while using two or four transmit antennas is different. For example, as shown in FIGS. 12 and 15, when the first antenna is used for cell search, only three frequency separations are possible. Accordingly, the number of distinguishable cells when using the frequency shifting technique with two or four transmission antennas is reduced by 50% from the number available when using a single transmission antenna. in this case. If the number of sequences is insufficient, the problem can be solved through a combination of sequence reuse and frequency shift.

Those skilled in the art through the above description can be seen that various changes and modifications can be made without departing from the spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

According to the present invention, there is an effect of generating a reference symbol for identifying a desired number of cells within a specific band.

Claims (17)

A method of configuring a reference signal for cell search, the method comprising: Generating a pseudo noise sequence of a first length; Using an orthogonal sequence, performing phase rotation on each component of the pseudo noise sequence to generate a first sequence; Mapping the first sequence to a reference signal; The reference signal is transmitted through at least one cell included in at least one cell group among cell groups reusing a sequence for cell discovery, and the reference signal is transmitted using a plurality of orthogonal subcarriers. Sending Including The cell group includes a plurality of cells corresponding to the type of the sequence for the cell search, and different cell groups reuse the sequence for the cell search. A method of constructing a reference signal for cell search. The method of claim 1, The cell ID is identified according to the type of the pseudo noise sequence of the specific length. A method of constructing a reference signal for cell search. The method of claim 1, The pseudo noise sequence of the first length is An orthogonal sequence generated according to the variable corresponding to the first length A method of constructing a reference signal for cell search. The method of claim 1, The pseudo noise sequence of the first length is A sequence in which some components of an orthogonal sequence generated according to a variable corresponding to the second length are removed A method of constructing a reference signal for cell search. The method of claim 1, Cell ID is identified according to the phase rotation value A method of constructing a reference signal for cell search. The method of claim 1, The pseudo noise sequence is a constant amplitude & zero autocorrelation (CAZAC) sequence. A method of constructing a reference signal for cell search. The method of claim 1, The reference signal is included in a subframe consisting of a specific number of OFDM symbols, The subframe includes two of the reference signals. A method of constructing a reference signal for cell search. The method of claim 7, wherein The first sequence is mapped to a reference signal included in one or two subframes. A method of constructing a reference signal for cell search. The method of claim 1, Performing a frequency shift according to control information to be transmitted through the first sequence Containing more A method of constructing a reference signal for cell search. The method of claim 1, The step of transmitting the reference signal, Transmitting through any one of a plurality of transmit antennas A method of constructing a reference signal for cell search. A method of configuring a reference signal for cell search, the method comprising: Generating a pseudo noise sequence of a first length; Using an orthogonal sequence, performing phase rotation on each component of the pseudo noise sequence to generate a first sequence; Mapping the first sequence to a reference signal by performing a frequency shift according to control information to be transmitted through the first sequence; Transmitting the reference signal using a plurality of orthogonal subcarriers How to configure a reference signal for cell search (cell search) comprising a. The method of claim 11, The cell ID is identified according to the type of the pseudo noise sequence of the specific length. A method of constructing a reference signal for cell search. The method of claim 11, The pseudo noise sequence of the first length is An orthogonal sequence generated according to the variable corresponding to the first length A method of constructing a reference signal for cell search. The method of claim 11, The pseudo noise sequence of the first length is A sequence in which some components of an orthogonal sequence generated according to a variable corresponding to the second length are removed A method of constructing a reference signal for cell search. The method of claim 11, Cell ID is identified according to the phase rotation value A method of constructing a reference signal for cell search. The method of claim 11, The pseudo noise sequence is a constant amplitude & zero autocorrelation (CAZAC) sequence. A method of constructing a reference signal for cell search. The method of claim 11, The step of transmitting the reference signal, Transmitting through any one of a plurality of transmit antennas A method of constructing a reference signal for cell search.

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