KR20100138126A - Method for selecting data transmission mode in distributed antenna system - Google Patents

Abstract

PURPOSE: A method for selecting a data transmission mode in a distributed antenna system is provided to give the feedback of the information corresponding to a data transfer mode by selecting the data transfer mode having a large value among calculated cell capacitance expectation values. CONSTITUTION: When receiving a pilot signal from a base station, an MS(Mobile Station) uses the received pilot signal to calculate a cell capacitance expectation value depending on a data transfer mode. The MS selects a data transfer mode having a large value among the calculated cell capacitance expectation values. The MS gives to the base station the feedback of the information corresponding to the data transfer mode, and receives the data from the base station at the selected data transfer mode.

Description

METHODO FOR SELECTING DATA TRANSMISSION MODE IN DISTRIBUTED ANTENNA SYSTEM}

The present invention relates to a data transmission mode selection method in a distributed antenna system, and more particularly, after a terminal receiving a pilot signal from a base station calculates an expected cell capacity according to a data transmission mode using the received pilot signal. In the method of selecting a data transmission mode in a distributed antenna system to ensure a high cell capacity irrespective of the position of a terminal in a cell by selecting a data transmission mode having a large value among the calculated cell capacity expected values and feeding it back to the base station. It is about.

Multiple Input Multiple Output (MIMO) systems, which can support multiple users, are well known for increasing frequency efficiency.

Among the MIMO systems, a distributed antenna system means that each transmit antenna is spread in a cell. For smooth communication, each distributed antenna is connected by a backbone that enables high-speed communication, and the synchronization of each antenna is all aligned.

This distributed antenna system is a macro for large scale fading because the position between each transmit antenna and the receive antenna of the terminal is different from the conventional cellular system where the base station at the center of the cell has all transmit antennas. Scoscopic diversity can be obtained.

In addition, the distributed antenna system may increase the channel capacity because the distance between the users located at the boundary of the cell and the transmission antenna is shorter.

In general, a transmission scheme applied to a distributed antenna system includes a spatial multiplexing transmission (SMT) and a single antenna transmission (SAT).

First, the spatial multiplexing transmission (SMT) method using a linear receiver can obtain a multiplexing gain because it has multiple receiving antennas, but in a multi-cell environment, the vicinity of a cell boundary is an interference from an adjacent cell. Since the effect of other cell interference (OCI) increases, the cell capacity of the terminal is sharply lowered near the cell boundary.

In addition, the antenna selection transmission method using the maximum ratio combining (MRC) receiver has better cell capacity than the spatial multiplexing transmission method because the influence of OCI is relatively small near the cell boundary, but the multiplexing gain is close to the cell center. ) To support low cell capacity.

As a result, each transmission scheme has a large and small relationship between cell capacity expectations depending on the location of the terminal. For example, when in the center of a cell, the effect of OCI is negligibly small regardless of the number, so that the SMT scheme which can obtain multiplexing gain is more than the antenna selective transmission (SAT) scheme. The cell capacity can be obtained.

On the contrary, when the terminal is located in the boundary area of the cell, the distance between the various transmitting antennas and the terminal in the cell increases, so that the antenna selective transmission (SAT) method using one transmitting antenna rather than the spatial multiplexing transmission (SMT) method This is likely to have greater spectral efficiency.

Therefore, there is a demand for a method capable of guaranteeing a constant cell capacity at any location.

It is a problem of the present invention to meet the above requirements.

Accordingly, the present invention calculates a cell capacity expected value according to the data transmission mode by the terminal receiving the pilot signal from the base station, and then selects a data transmission mode having a large value from the calculated cell capacity expected values. It is an object of the present invention to provide a method for selecting a data transmission mode in a distributed antenna system for ensuring a high cell capacity regardless of the position of a terminal in a cell.

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention which are not mentioned can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

In the method of the present invention for achieving the above object, in the method of selecting a data transmission mode, as the terminal receives a pilot signal from the base station, using the received pilot signal to calculate the cell capacity expected according to the data transmission mode ; Selecting, by the terminal, a data transmission mode having a large value among the calculated cell capacity expected values and feeding back to the base station; And receiving, by the terminal, data from the base station in the selected data transmission mode.

The present invention can increase the cell capacity through the switching of the data transmission mode when using a distributed antenna system (Distributed Antenna System).

In the present invention as described above, the terminal receiving the pilot signal from the base station calculates the cell capacity expected value according to the data transmission mode by using the received pilot signal, the data transmission mode having a larger value among the calculated cell capacity expected value By selecting the feedback to the base station, it is possible to ensure a high cell capacity regardless of the position of the terminal in the cell.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, It can be easily carried out. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is an exemplary diagram for a multi-cell environment-based distributed antenna system to which the present invention is applied.

As shown in FIG. 1, circles indicated by dotted lines represent each cell 10, and circles indicated by solid lines represent communication areas 20 of respective distributed antennas.

Therefore, the distributed antenna system has a multi-cell structure having six cells adjacent to the center cell, and each cell has a total of seven transmit antennas (one center antenna and six distributed antennas 40 owned by the base station 30). ) Is located.

Since such a distributed antenna system has a structure different from that of a conventional cellular system, some conditions must be satisfied.

First, each cell 10 uses the same frequency. This increases the frequency efficiency.

In addition, the distributed antenna 40 is connected to each base station 30 in the cell center by a cable. At this time, the cable ensures high-speed and reliable communication, and does not adversely affect synchronization between distributed antennas, and performs all functions of the antennas easily.

In addition, the present invention assumes a single user scenario for ease of understanding. In this case, the transmitting antenna selects the path loss in the order of the smallest pathloss.

In addition, since each distributed antenna 40 includes an amplifier, it has a maximum power constraint.

를 송신할 때, 홈 셀(j = 0)에 속한 특정 단말에서 관찰되는 수신신호는 하기의 [수학식 1]과 같이 나타낼 수 있다.Under this assumption, through the transmit antenna k in the peripheral cells (j = 1,2,3,4,5,6)

When transmitting, the received signal observed in a specific terminal belonging to the home cell (j = 0) may be represented by Equation 1 below.

로서 홈 셀(j = 0)의 각 송신 안테나를 통해 송신된 신호를 나타내며, 우변 첫째 항은 원하는 신호를 나타내고, 둘째 항은 OCI(Other Cell Interference)를 나타내며, 셋째 항은 AWGN(Additive White Gaussian Noise)를 나타낸다.here,

As a signal transmitted through each transmit antenna of the home cell (j = 0), the first term on the right side represents the desired signal, the second term represents Other Cell Interference (OCI), and the third term is AWGN (Additive White Gaussian Noise). ).

는

널(Null) 행렬을 나타내고, 대규모 페이딩(large scale fading)(

)과 소규모 페이딩(small scale fading)(

)을 모두 포함하며, 각 열을 구성하는

는 0 번째 셀(home cell)의 m_i 번째 송신 안테나와 수신 안테나 간의 채널을 나타낸다.Also,

Is

Represents a null matrix and uses large scale fading (

) And small scale fading (

), And make up each column

Denotes a channel between the m _i th transmit antenna and the receive antenna of the 0 th cell.

은 크게 그림자 효과(shadowing effect)와 경로손실 효과(pathloss effect)가 고려된 마크로스코픽 페이딩(macroscopic fading)을 나타낸다.Here, since there may be several receiving antennas, the receiving antennas are represented in a vector form. Also,

Shows macroscopic fading, which considers the shadowing effect and the pathloss effect.

In addition, in the case where n cells of six cells adjacent to the home cell transmit signals through only one antenna, and m (6-n) cells transmit signals using a plurality of antennas, the equation The second and third terms of 1] can be expressed as Equation 2 below.

Here, the dispersion of Equation 2 may be expressed as Equation 3 below.

는 셀 j의 송신 안테나 k의 송신전력을 나타낸다.In Equations 2 and 3, q _j represents an index of a transmission antenna selected from n cells.

Denotes the transmit power of the transmit antenna k of cell j.

2 is a flowchart illustrating a method of selecting a data transmission mode in a distributed antenna system according to the present invention.

First, a distributed antenna system to which the present invention is applied includes a linear receiver for transmitting data in a spatial multiplexed transmission (SMT) scheme and a maximum ratio combining receiver (MRC) for transmitting data in an antenna selective transmission scheme. Doing.

Thereafter, the base station transmits a pilot signal to the terminal (201).

Then, the terminal calculates a cell capacity expectation value for each data transmission mode using the received pilot signal (202).

At this time, the cell capacity expectation of the spatial multiplexing transmission method is equal to the average of the maximum data rate sum of each antenna calculated for a predetermined time.

This is calculated using Equation 4 below.

는 각 m번째 송신 안테나로부터 받은 신호의 신호대간섭잡음비(SINR: Signal to Interference Noise Ratio)를 나타낸다. 이때, N_R은 단말기의 전체 안테나의 수이고, N_T는 송신 안테나의 수이다.Here, M represents min (N _T , N _R ), which is the rank of the channel,

Denotes a Signal to Interference Noise Ratio (SINR) of a signal received from each m-th transmit antenna. In this case, N _R is the total number of antennas of the terminal and N _T is the number of transmit antennas.

In addition, the expected cell capacity of the Single Antenna Transmission (SAT) method for obtaining a reception diversity gain through one transmission antenna and a plurality of reception antennas is equal to the average of the maximum transmission rates calculated for a predetermined time period.

This is calculated using Equation 5 below.

는 'Frobenius norm'을 나타내며,

은 선택된 하나의 송신 안테나 전력을 의미한다.here,

Represents 'Frobenius norm',

Denotes the power of one selected transmit antenna.

In Equations 4 and 5, E means an average, C _E means an averaged cell capacity, and C _I means an instantaneous cell capacity.

Thereafter, a data transmission mode having a large value is selected from the calculated cell capacity expected values, and corresponding information is transmitted to the base station (203). At this time, the instantaneous cell capacity expectation and the average cell capacity expectation are as follows.

)은 하기의 [수학식 6]을 통해 선택한다.Expected instantaneous capacity: The calculated value of instantaneous cell capacity each time each symbol is transmitted, which is a criterion for selecting a data transmission mode. At this time, the instantaneous cell capacity having a large value among the instantaneous cell capacity expectations for each data transmission mode (

) Is selected through Equation 6 below.

Here, since Equation 6 selects a transmission technique having a large cell capacity each time, more cell capacity can be obtained than an algorithm based on averaged cell capacity, but there is too much information to be fed back.

)은 하기의 [수학식 7]을 통해 선택한다.Expected average cell capacity (ergodic capacity): The average cell capacity of a symbol is calculated for each data transmission mode, which is a criterion for selecting a data transmission mode. In this case, the averaged cell capacity having a larger value among the averaged cell capacity expectations for each data transmission mode (

) Is selected through Equation 7 below.

[Equation 7] has the advantage that the overall cell capacity is smaller than when selecting the data transmission mode by comparing the instantaneous cell capacity expectation, but the amount of feedback data is much easier to implement.

Then, the base station transmits data in the data transmission mode received from the terminal (204).

Hereinafter, a simulation result of a data transmission mode selection method in the distributed antenna system according to the present invention will be described with reference to FIGS. 3 and 4.

First, in order to verify the performance of the present invention, a simulation was performed using the parameters shown in Table 1 below.

In addition, in the embodiment of the present invention, a minimum mean squared error (MMSE) receiver having a good performance among linear receivers whose decoding is relatively simple is used.

라고 할 때, MMSE 수신기의 정합 필터(matched filter)의 행렬은 하기의 [수학식 8]과 같이 나타낼 수 있다.Therefore, the detected signal

In this case, the matrix of the matched filter (matched filter) of the MMSE receiver can be expressed as Equation 8 below.

는 각 송신 안테나의 전력을 나타낸다. 이러한 환경에서, 정합 필터(matched filter)를 곱한 후 얻을 수 있는 'post-processing SINR' 값은 하기의 [수학식 9]와 같다.here,

Denotes the power of each transmit antenna. In this environment, the 'post-processing SINR' value obtained after multiplying a matched filter is expressed by Equation 9 below.

는 MMSE 수신기를 이용한 공간 다중화 전송(SMT) 방식의 m번째 송신신호의 SINR값을 나타낸다.here,

Denotes the SINR value of the m th transmission signal of the SMT scheme using the MMSE receiver.

FIG. 3 is a simulation result diagram of a method for selecting a data transmission mode in a distributed antenna system according to the present invention, wherein an expected value of a cell capacity according to each data transmission mode is a distance between a terminal and a cell center base station, that is, 'normalized' change according to 'distance'.

As shown in Figure 3, it can be seen that the method proposed in the present invention can obtain a higher cell capacity compared to the conventional methods.

에 따라 변화하는 모습을 나타낸다.FIG. 4 is a simulation result diagram of another embodiment of a data transmission mode selection method in a distributed antenna system according to the present invention.

The appearance changes according to.

값에서 종래의 방법들보다 높은 셀 용량을 얻을 수 있음을 알 수 있다.As shown in Figure 4, the method proposed in the present invention is

It can be seen from the value that a higher cell capacity can be obtained than conventional methods.

On the other hand, the method of the present invention as described above can be written in a computer program. And the code and code segments constituting the program can be easily inferred by a computer programmer in the art. In addition, the written program is stored in a computer-readable recording medium (information storage medium), and read and executed by a computer to implement the method of the present invention. The recording medium may include any type of computer readable recording medium.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

The present invention can be used for distributed antenna MIMO system.

1 is an exemplary view of a distributed antenna system based on a multi-cell environment to which the present invention is applied;

2 is a flowchart illustrating a method of selecting a data transmission mode in a distributed antenna system according to the present invention;

3 is a simulation result diagram of an embodiment of a data transmission mode selection method in a distributed antenna system according to the present invention;

4 is a simulation result diagram of another embodiment of a data transmission mode selection method in a distributed antenna system according to the present invention.

* Explanation of symbols for the main parts of the drawings

10: cell 20: communication area of a distributed antenna

30: base station 40: distributed antenna

Claims (7)

In the data transmission mode selection method, Calculating a cell capacity expectation according to a data transmission mode using the received pilot signal as the terminal receives a pilot signal from a base station; Selecting, by the terminal, a data transmission mode having a large value among the calculated cell capacity expected values and feeding back to the base station; And The terminal receiving data from the base station in the selected data transmission mode Data transmission mode selection method comprising a. The method of claim 1, The cell capacity expectation, A data transmission mode selection method comprising a cell capacity expectation of a spatial multiplexing transmission scheme and a cell capacity expectation of an antenna selection transmission scheme. The method of claim 2, The expected cell capacity of the spatial multiplexing transmission scheme is A method of selecting a data transmission mode, characterized in that the average of the maximum transmission rate sum for each antenna calculated for a predetermined time. The method of claim 3, wherein The expected cell capacity of the spatial multiplexing transmission scheme is A method of selecting a data transmission mode calculated by using Equation A below. Equation A

(Where M represents min (N _T , N _R ), which is the rank of the channel,

Denotes the signal-to-interference noise ratio of the signal received from each mth transmit antenna.) The method of claim 2, The expected cell capacity of the antenna selective transmission scheme is Method for selecting a data transmission mode, characterized in that the average of the maximum transmission rate calculated for a certain time. The method of claim 5, The expected cell capacity of the antenna selective transmission scheme is A method of selecting a data transmission mode calculated by using Equation B below. Equation B

(here,

Represents 'Frobenius norm',

Denotes the power of one transmit antenna selected.) 7. The method according to any one of claims 1 to 6, The terminal, A method for selecting a data transmission mode comprising a linear receiver for transmitting data in a spatial multiplexing transmission scheme and an MRC receiver for transmitting data in an antenna selection transmission scheme.

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