KR100597835B1 - Cellular orthogonal frequency division multiple access system to distinguish signals of each cell by using midamble - Google Patents

Abstract

The present invention facilitates channel estimation by a mobile terminal located in each cell using a midamble of a downlink frame, and cellular orthogonality for distinguishing a signal of a cell in which the cell is located. The present invention relates to a frequency orthogonal frequency division multiple access system.

In the cellular orthogonal frequency division multiple access system of the present invention, mobile stations located in a plurality of cells each include a midamble having information of the cell from a base station of the cell in which the cell is located. The received downlink frame, the downlink frame has a different form of the midamble pattern (Pattern) for each cell, the base station transmits the midamble pattern information of its downlink frame to the mobile terminal of the cell.

Channel Estimation, Midamble, Symbol, Subcarrier, Cellular, OFDM

Description

CELLULAR ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS SYSTEM TO DISTINGUISH SIGNALS OF EACH CELL BY USING MIDAMBLE}

1 is a diagram illustrating a cell arrangement in case of frequency reuse in a conventional time division multiple access or frequency division multiple access cellular system.

2 is a frame diagram of a conventional cellular orthogonal frequency division multiple access system for distinguishing adjacent cells using a midamble symbol disclosed in IEEE 802.16.

FIG. 3 is a diagram illustrating a configuration of a frame having midamble symbols at different positions for each cell or sector in the time domain in the cellular orthogonal frequency division multiple access system according to the present invention.

FIG. 4 is a diagram illustrating an embodiment of a cell arrangement plan for each midamble symbol index when the midamble symbol interval of a downlink frame is 4 as shown in FIG. 3.

FIG. 5 is a diagram illustrating another downlink frame corresponding to each cell when differentiating each cell using subcarriers of different frequencies with respect to the midamble symbol at a specific position according to another embodiment of the present invention.

FIG. 6 is a diagram illustrating an embodiment of a cell allocation plan for each midamble subcarrier index when the interval between midamble subcarriers is 3 in a downlink frame as shown in FIG. 5.

The present invention relates to a cellular orthogonal frequency division multiple access (OFDMA) system. In particular, mobile terminals located in each cell can transmit their own cell signals using a midamble. A cellular orthogonal frequency division multiple access system is provided.

In a mobile communication environment, a cell refers to an area where a call can be made using radio waves generated by one base station. In addition, a system implemented by dividing the area into cell units is called a cellular system. In a cellular system, since users receive signals from one base station on a cell basis, performance degradation of the system may occur due to signal interference by base stations of adjacent cells at a cell edge. If each cell uses a different frequency signal to communicate with each other, the performance degradation of the system due to signal interference between adjacent cells may be improved. However, due to the limited frequency band available, it is practically impossible to use different frequencies for all cells. Therefore, frequency reuse for efficiently placing inter-cell frequencies using a limited frequency band is essential.

1 is a diagram illustrating a cell arrangement in case of frequency reuse in a conventional time division multiple access or frequency division multiple access cellular system. 1 is a cell arrangement in the case of reusing the frequency in seven cell units (that is, frequency reuse coefficient = 7). As shown in FIG. 1, in a conventional time division multiple access (TDMA) or frequency division multiple access (FDMA) cellular system that reuses frequencies, different frequencies are used between adjacent cells. In the next cell where interference is canceled, the same frequency is reused again to distinguish signals between adjacent cells under a limited frequency resource. That is, cells are repeatedly arranged in units of seven cells using different frequencies. However, the signal interference of adjacent cells appearing at the edges of each cell still exists, and the lower the frequency reuse coefficient (frequency reuse coefficient = "1"), the worse the performance degradation of the cellular system due to signal interference.

On the other hand, in a cellular system of code division multiple access (CDMA), all cells share a frequency with one wide bandwidth. That is, in the code division multiple access scheme, the frequency reuse factor is "1". Instead, the cellular system of the code division multiple access method uses a spread spectrum method, and the processing gain of the system due to signal interference between adjacent cells through the processing gain obtained in the process of spreading the band and then despreading again. Improve performance deterioration On the other hand, in the orthogonal frequency division multiple access cellular system, the performance of the system by the signal interference between adjacent cells using the coding gain and the average effect of the signal interference between adjacent cells obtained during the encoding / decoding process for the signal channel Improve deterioration However, this method is not as effective as the code division multiple access method. Recently, the method of distinguishing signals between adjacent cells using a midamble symbol having a unique value for each cell or sector has been used. Electronics Engineers).

2 is a frame diagram of a conventional cellular orthogonal frequency division multiple access system for separating signals between adjacent cells using a midamble symbol disclosed in IEEE 802.16d.

As shown in FIG. 2, the frame proposed by IEEE 802.16 divides a downlink frame into a preamble 20, data symbols 22, and midamble symbols 24 in the time domain. The preamble 20 includes control information of the corresponding base station and is located at the front of the downlink frame. The data symbols 22 contain actual data transmitted from the base station to each mobile terminal. The midamble symbols 24 include base station information and unique information of the corresponding cell or sector for each cell or sector, and the midamble symbols use amplified signals rather than general data symbols. In IEEE 802.16, the midamble symbols 24 are fixedly arranged at the same position on each downlink frame for all cells or sectors at fixed intervals. The mobile terminals located in a specific cell or sector refer to the information included in the midamble symbol 24 of the received downlink frame to determine a signal from the corresponding base station in which the mobile station is located. That is, each of the mobile terminals uses the unique information included in the midamble symbol 24 to determine the downlink frame of the base station in which the corresponding base station is located among the received downlink frames. However, this method also uses the same midamble pattern so that mobile terminals located in each cell or sector at the edge of each cell or sector do not completely distinguish signals of the corresponding cell in which they are located.

SUMMARY OF THE INVENTION An object of the present invention is a cellular orthogonal frequency division multiple access system in which mobile terminals located in each cell or sector distinguish signals of corresponding cells in which they are located by using midamble symbols of different positions in the time domain for each cell or sector. To provide.

It is still another object of the present invention to provide a cellular orthogonal frequency division multiple access system using cellular orthogonal frequency division multiplexing that separates signals between adjacent cells using subcarriers of different frequencies for each cell or sector for a midamble symbol at a specific location. To provide a connection system.

In the cellular orthogonal frequency division multiple access system of the present invention, mobile terminals located in a plurality of cells receive a downlink frame including a midamble having information of the corresponding cell from a base station of the corresponding cell in which the cell is located. In this case, the received downlink frames have different types of midamble patterns for each cell, and the base station transmits midamble pattern information of the downlink frame allocated to the cell to which the mobile station belongs.

(Example)

FIG. 3 is a diagram illustrating a configuration of a frame having midamble symbols at different positions for each cell or sector in the time domain in the cellular orthogonal frequency division multiple access system according to the present invention. Referring to FIG. 3, a frame transmitted between a base station and a mobile terminal is classified into a downlink frame transmitted from a base station to mobile terminals and an uplink frame transmitted from a mobile terminal to a base station. A guard band (TTG: Transmit / receive Transition Gap) is provided between the downlink frame and the uplink frame to prevent crosstalk of the signal.

The downlink frame includes a predetermined interval between the preambles 300a, 300b, 300c, and 300d including the control information of the corresponding base station and the data symbols 301a and the data symbols 301a transmitted from the actual base station to the respective mobile terminals. The midamble symbols 302, 304, 306, and 308 arranged as are included. The midamble symbols 302, 304, 306, and 308 include unique information of a corresponding cell or sector and base station information.

In the present invention shown in FIG. 3, the midamble symbols 302, 304, 306, and 308 are configured at different positions of the downlink frame for each cell or sector. As shown in FIG. 3, when the interval between the midamble symbol and the next midamble symbol is 4 (k = 4) in a downlink frame used in one cell or sector, up to four distinct downlinks may be distinguished. Frame configuration is possible. That is, up to four cell or sector units having different downlink frames can be distinguished.

FIG. 4 is a diagram illustrating an embodiment of a cell arrangement plan for each midamble symbol index y when the midamble symbol interval k of the downlink frame is 4 as shown in FIG. 3. The midamble symbol index y is an index corresponding to the positions of the first midamble symbols 302a, 302b, 302c, and 302d in each downlink frame in FIG. 3. That is, the position of the midamble symbol in each downlink frame varies according to the value of the midamble symbol index y. As shown in the embodiment of cell planning of FIG. 4, different midamble symbol indices y are assigned to immediately adjacent cells. In other words, adjacent cells use downlink frames having different positions of the midamble symbol.

3 and 4, (a) of FIG. 3 is a downlink frame used in cells corresponding to the case where the midamble symbol index y is 4 in FIG. 4, and FIG. A downlink frame used in cells corresponding to the case where the amble symbol index y is three. In addition, (c) of FIG. 3 is a downlink frame used in cells corresponding to the case where the midamble symbol index y is 2, and (d) of FIG. 3 is cells having the midamble symbol index y of 1. Downlink frame used in.

As described above, in the embodiments of the present invention shown in FIGS. 3 and 4, downlink frames having the same type, that is, downlink frames having the same position of the midamble symbol, are not used for adjacent cells. Maximum signal separation effect can be obtained.

Meanwhile, in the embodiments of FIG. 3 and FIG. 4, the corresponding base station of each cell controls the mobile station located in its cell to control the location information midamble_symbol _y of the midamble symbol used in the downlink frame of the corresponding cell. Channel). Each mobile station performs channel estimation using the midamble symbol position information (midamble_symbol _y ) of the cell in which it is received from the base station through the midamble symbol of the corresponding position.

The midamble symbol position information midamble_symbol _y in each downlink frame according to the midamble symbol index y may be obtained by Equation 1 below.

midamble_symbol _y = k × n + y

Where k is the midamble interval, n is the symbol coefficient, y is the midamble symbol index, and the symbol coefficient n = {0, 1, ..., m}, and m is the total number of symbols (T). ) / Maximum integer less than -1 midamble spacing (k))

In (a) of FIG. 3, that is, when the midamble symbol index y is 4, the position information midamble_symbol ₄ of the midamble symbol is calculated as shown in Equation 2 using Equation 1 above. (The midamble spacing k is 4 and the total number of symbols T is 16 in FIG. 3. In Equation 1 above, k = 4 and m = 3.)

midamble_symbol ₄ = 4 × n + 4

Substituting 0, 1, 2, 3 into n in the above Equation 2, position information (midamble_symbol ₄ ) of the midamble symbols 302a, 304a, 306a, and 308a corresponding to (a) of FIG. ) Is calculated as 4, 8, 12, 16.

Similarly, (b) of FIG. 3 having a midamble symbol index y of 3, (c) of FIG. 3 having a midamble symbol index y of 2, and of FIG. 3 of FIG. Also for d), the position information (midamble_symbol ₃ , midamble_symbol ₂ , midamble_symbol ₁ ) of each midamble symbol may be calculated using Equation 1 above.

FIG. 5 shows another downlink frame corresponding to each cell when different cells are identified using subcarriers of different frequencies with respect to midamble symbols at specific positions arranged at regular intervals. Drawing. In the embodiment of FIG. 5, unlike the embodiment of FIG. 3 in which the positions of the midamble symbols are changed according to the midamble symbol index y assigned to each cell, they are located at the same position of the downlink frame for all cells and sectors. The symbol is used as the midamble symbols 502, 504, 506, and 508. In addition, the division of each cell uses a combination of subcarriers included in the midamble symbols 502, 504, 506, and 508. Hereinafter, subcarriers used as midambles are referred to as midamble subcarriers. As shown in FIG. 5, the midamble subcarriers may be freely allocated and used within a range not overlapping each other for each cell. FIG. 5 specifically shows that each symbol consists of 10 subcarriers, the interval between midamble symbols used in each cell is 4, and the interval between midamble subcarriers used as actual midambles in each midamble symbol (Ψ). If it is constantly allocated to 3, it is a downlink frame used for each cell. When the interval Ψ between the midamble subcarriers is 3 as shown in FIG. 5, up to three different downlink frames may be configured as shown in (a), (b), and (c).

FIG. 6 is a diagram illustrating an embodiment of a cell arrangement plan for each midamble subcarrier index y ′ when the interval Ψ between midamble subcarriers is 3 in a downlink frame as shown in FIG. 5. In the embodiment of FIG. 6, similarly to FIG. 4, by providing different midamble subcarrier indexes y ′ to adjacent cells, channel estimation is performed on the adjacent cells by using midamble subcarriers of different positions. .

5 and 6, FIG. 5A illustrates a downlink frame when the midamble subcarrier index y ′ is 1, and FIGS. 5B and 5C illustrate midamble subcarrier indexes y ') is a downlink frame when 2 and 3, respectively.

Meanwhile, in the embodiments of FIG. 5 and FIG. 6, the corresponding base station of each cell transmits the position information (midamble_subcarrier _{y ′} ) of the midamble subcarrier used in the downlink frame of the cell to mobile terminals located in the cell. Transmission through Control Channel Each mobile terminal performs channel estimation using the midamble subcarrier position information (midamble_subcarrier _{y ′} ) of the cell in which the mobile station is received from the base station through the midamble subcarrier of the corresponding position.

The midamble subcarrier position information midamble_subcarrier _{y '} in each downlink frame according to the midamble subcarrier index y' may be obtained by Equation 3 below.

midamble_subcarrier _y´ = ψ × △ f + y´

(Where ψ is midamble subcarrier spacing, Δf is subcarrier coefficient, y´ is midamble subcarrier index, and subcarrier coefficient Δf = {0, 1, ..., m´}, and m´ is ( Total subcarriers (N) / maximum integer less than midamble subcarrier spacing (ψ))

In the above [Equation 3] (a) of Figure 5 using i.e., midamble sub-carrier index (y') the position information (midamble_subcarrier ₁₎ of the midamble sub-carriers when the first is expressed as the following formula 4; (In FIG. 5, since the midamble subcarrier spacing (ψ) is 3 and the total subcarrier number (N) is 10. In Equation 3, ψ = 3 and m ′ = 3.) The value of the amble subcarrier position information midamble_subcarrier _y 'does not exceed the total number of subcarriers (N).

midamble_subcarrier ₁ = 3 × Δf + 1

Substituting 0, 1, 2, and 3 into Δf in Equation 4 above, the position information midamble_subcarrier ₁ of the midamble subcarrier corresponding to (a) of FIG. 5 is 1, 4, 7, and 10. Is calculated.

Similarly, the position information (midamble_subcarrier) of each midamble subcarrier also applies to (b) of FIG. 5 having a midamble subcarrier index y 'and to (c) of FIG. 5 having a midamble subcarrier index y' 3. ₂ , midamble_subcarrier ₃ ) may be calculated using Equation 3 above.

In the above, the midamble configuration of the cellular orthogonal frequency division multiple access system according to the present invention has been described above with reference to the above drawings, but this is merely exemplary and various applications and modifications can be made without departing from the technical spirit of the present invention. Do. That is, the configuration of the midamble using the combination of the two embodiments of the present invention described above is possible, and not only the cell unit but also the sector unit.

As described above, the cellular orthogonal frequency division multiple access system of the present invention uses different unique midamble patterns for each of adjacent cells or sectors, thereby distinguishing signals between adjacent cells at both the inside and the edge of the cell or sector. Can be. In addition, through this, each mobile terminal can easily estimate its own channel.

Claims (26)

A plurality of cells; A plurality of base stations, each downlink frame having a midamble pattern corresponding to a respective cell, which generates a plurality of downlink frames, the midamble pattern having a plurality of midambles arranged regularly at regular intervals; ; And A mobile orthogonal frequency division multiple access system comprising a mobile terminal for receiving a downlink frame from one base station and detecting the midamble pattern from the received downlink frame to track the location of a cell. The method of claim 1, And a midamble pattern of adjacent cells among the plurality of cells is different from each other. The method of claim 1, Cellular orthogonal frequency division multiple access system, characterized in that the midamble pattern of the non-adjacent cells of the plurality of cells are the same. The method of claim 1, The midamble pattern includes a plurality of midambles having equal intervals in the time domain of the downlink frame, wherein the interval between the plurality of midambles and the preamble is provided as position information of a cell. system. The method of claim 4, wherein And the interval with the preamble is the interval with the midamble closest to the preamble in the time domain. The method of claim 5, The mobile terminal measures a distance between the preamble and the midamble and tracks the position of the cell. delete The method of claim 4, wherein And a downlink frame of non-adjacent cells among the plurality of cells has the same temporal position of the midamble. The method of claim 4, wherein And a downlink frame of adjacent cells among the plurality of cells has different temporal positions of the midambles. The method of claim 1, Each of the plurality of midamble patterns has the midamble located at the same position in the time domain on the downlink frame, and the midamble has a pilot subcarrier pattern corresponding to each cell in the frequency domain, wherein the pilot subcarrier pattern has a frequency interval. A cellular orthogonal frequency division multiple access system comprising the same plurality of pilot subcarriers. The method of claim 10, A cellular orthogonal frequency division multiple access system, wherein pilot subcarrier patterns of adjacent cells among the plurality of cells are different from each other. The method of claim 10, And a pilot subcarrier pattern of non-adjacent cells among the plurality of cells is the same cellular orthogonal frequency division multiple access system. delete The method of claim 10, And the base station transmits position information of a cell corresponding to the pilot subcarrier pattern. The method of claim 14, The mobile terminal performs channel tracking of the corresponding location by using the received location information of the cell. A plurality of cells; Each downlink frame, which generates a plurality of downlink frames, includes a plurality of midambles, the plurality of midambles comprising: a plurality of base stations constituting a plurality of midamble patterns corresponding to respective cells in a time domain; And A mobile orthogonal frequency division multiple access system comprising a mobile terminal for receiving a downlink frame from one base station and detecting the midamble pattern from the received downlink frame to track the location of a cell. The method of claim 16, And the mobile terminal tracks the position of the cell by measuring a distance between the midamble closest to the preamble in the received downlink frame. The method of claim 16, And wherein said midamble is repeated at equal time intervals on said downlink frame. The method of claim 16, A cellular orthogonal frequency division multiple access system, wherein the midamble patterns of adjacent cells among the plurality of cells are different from each other. The method of claim 16, A cellular orthogonal frequency division multiple access system, wherein the midamble patterns of non-adjacent cells among the plurality of cells are the same. A plurality of cells; The midamble includes a plurality of pilot subcarriers having the same midamble pattern in the time domain, but having a same frequency interval in the frequency domain, which generates a downlink frame including a plurality of midambles. A plurality of base stations constituting a corresponding plurality of pilot subcarrier patterns; And And a mobile terminal for receiving a downlink frame from any one base station and detecting the pilot subcarrier pattern from the received downlink frame to track the location of the cell. delete The method of claim 21, And the mobile station performs channel estimation using the position information of the pilot subcarrier of the minimum frequency. delete The method of claim 21, And the pilot subcarrier patterns of adjacent cells among the plurality of cells are different from each other. The method of claim 21, And the pilot subcarrier patterns corresponding to non-adjacent cells of the plurality of cells are identical to each other.

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