KR102177054B1 - LTE Inter-Cell Interference mitigation method - Google Patents

Abstract

The present invention relates to an apparatus and method for avoiding interference between LTE cells, which can improve quality degradation due to inter-cell interference in an LTE system.
In addition, according to the present invention, a cell coverage checker that checks the cell coverage of a serving cell and selects a line of sight (LOS) cell when the cell coverage exceeds a first threshold; A pollution cell determiner for determining whether the wide area line of sight cell selected by the cell coverage checker is a PCI pollution cell; A target cell selector for selecting a frequency shift target cell by checking a cut rate among PCI pollutant cells determined by the pollutant cell determiner; And a shift frequency selector for selecting a shift frequency in consideration of a frequency raster and a guard band available in LTE for the frequency shift target cell selected by the target cell selector. An avoidance device and method can be provided to improve the signal-to-noise ratio.

Description

LTE inter-cell interference avoidance apparatus and method {LTE Inter-Cell Interference mitigation method}

The present invention relates to an apparatus and method for avoiding interference between LTE cells, which can improve quality degradation due to inter-cell interference in an LTE system.

In the case of LTE (Long Term Evolution), intra-cell interference does not occur by using DL OFDMA & UL SC-FDMA. However, interference occurs between cells of the same frequency.

3GPP is providing a function to minimize inter-cell interference through functions such as ICIC or eICIC, but if the function is actively used to separate the inter-cell used frequency (FFR), the cell capacity decreases and the game is dynamically played. In the case of trying to avoid cell interference, there is a problem in that the interference avoidance performance is degraded due to the ICIC signal delay of the X2 interface.

As another method, in the case of forward inter-cell interference, base station output adjustment, sector separation and ISD (Inter Site Distance) design optimization, base station antenna tilting and swing optimization. , It is possible to overcome to some extent through the selection of vertical/horizontal beam-width & gain. In the case of the reverse direction, interference avoidance between cells can be expected through an appropriate ISD design.

However, even this method is difficult to expect a great effect in suburbs or seas having a large LOS (Line Of Sight) when transmitting radio waves in an open space.

Particularly, in the sea where the radio wave reach is longer than on the ground, the quality of the maritime service cell is frequently deteriorated by the radio wave of the terrestrial service cell.

That is, in the case of radio waves transmitted by base stations or terminals in dense urban or sub urban, LOS (Line Of Sight) is limited by various structures.

However, in an environment where a relatively long LOS is guaranteed, such as in suburbs or sea, the reach of radio waves increases, causing PCI (Physical Cell ID) pollution easily, and forward and reverse quality deterioration due to inter-cell interference may occur.

Korean Publication No. 10-2010-0115653 Korean Publication No. 10-2011-0077663 Japanese Patent Registration No. 5632456 International Publication No. WO2016/064247

Accordingly, the present invention has been devised to solve the above problems, and to improve the signal-to-noise ratio (SINR) of a cell with extreme forward or reverse inter-cell interference by shifting the center frequency to reduce inter-cell interference. It is to provide an apparatus and method for avoiding interference between LTE cells.

An apparatus according to an aspect of the present invention is a cell coverage checker that checks the cell coverage of a serving cell and selects a line of sight (LOS) cell when the cell coverage exceeds a first threshold. ; A pollution cell determiner for determining whether the wide area line of sight cell selected by the cell coverage checker is a PCI pollution cell; A target cell selector for selecting a frequency shift target cell by checking a cut rate among PCI polluted cells determined by the pollutant cell determiner; And a shift frequency selector for selecting a shift frequency in consideration of a frequency raster and a guard band available in LTE for the frequency shift target cell selected by the target cell selector.

In addition, the cell coverage checker of the device according to an aspect of the present invention checks the cell coverage of the serving cell by using timing advance (TA) statistics included in a random access response (RAR) message to determine cell coverage. When is over the first threshold, a line of sight (LOS) cell is selected.

In addition, the pollutant cell determiner of the device according to an aspect of the present invention calculates the number of intra-frequency neighbor cells of the wide-area line of sight cells selected by the cell coverage checker to determine whether or not a PCI pollutant cell is present. When it checks and exceeds the second threshold, it is determined as a PCI pollution cell.

In addition, the shift frequency selector of the apparatus according to an aspect of the present invention shifts a frequency of 200 kHz with respect to a center frequency for the frequency shift target cell selected by the target cell selector.

On the other hand, the method according to an aspect of the present invention is (A) the cell coverage checker checks the cell coverage of the serving cell, and when the cell coverage exceeds a first threshold, a line of sight (LOS) Sight) selecting a cell; (B) the pollutant cell determiner determining whether the wide area line of sight cell selected by the cell coverage checker is a PCI pollutant cell; (C) a target cell selector selecting a frequency shift target cell by checking a call disconnection rate among PCI polluted cells determined by the pollutant cell determiner; And (D) the shifted frequency selector selecting a shift frequency in consideration of a frequency raster and a guard band available in LTE for the frequency shift target cell selected by the target cell selector. Includes.

In addition, step (A) of the method according to an aspect of the present invention includes (A-1) the cell coverage checker of the serving cell by using timing advance (TA) statistics included in a random access response (RAR) message. Checking cell coverage; And (A-2) selecting, by the cell coverage checker, as a line of sight (LOS) cell when the confirmed cell coverage exceeds a first threshold.

In addition, step (B) of the method according to an aspect of the present invention includes (B-1) an intra-frequency neighbor cell of a wide-area line of sight cell selected by the cell coverage checker by the pollution cell determiner. Checking the number of; And (B-2) determining, by the pollutant cell determiner, that the number of adjacent cells in the frequency exceeds a second threshold as a result of the determination as a PCI pollutant cell.

In addition, in step (D) of the method according to an aspect of the present invention, the shift frequency selector shifts a frequency of 200 kHz with respect to a center frequency with respect to the frequency shift target cell selected by the target cell selector.

According to the present invention, the forward and reverse signal-to-noise ratio (SINR) can be improved by shifting the center frequency to minimize inter-cell interference.

1 is an exemplary diagram for a degree of inter-cell interference according to a general LOS and ISD.
FIG. 2 is a diagram illustrating a cell in which a center frequency is shifted and one sub-carrier of each cell using a conventional center frequency in a frequency domain according to an embodiment of the present invention.
FIG. 3 shows a difference in signal-to-noise ratio (SINR) due to inter-cell interference in the case of applying a 200 kHz shift and in the case of a normal cell.
4 is a block diagram of an LTE intercell interference avoiding apparatus according to a preferred embodiment of the present invention.
5 is a flowchart of a method of avoiding LTE intercell interference according to an exemplary embodiment of the present invention.
6 is a conceptual diagram of a method of avoiding interference between LTE cells according to a preferred embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily implement the embodiments of the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and similar reference numerals are assigned to similar parts throughout the specification.

Throughout the specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

In this specification, the terminal is a mobile station (MS), a mobile terminal (MT), a subscriber station (SS), a portable subscriber station (PSS), and a user device (User Equipment, UE), an access terminal (AT), and the like, and may include all or part of functions such as a mobile terminal, a subscriber station, a mobile subscriber station, and a user device.

In the present specification, a base station (BS) is an access point (AP), a radio access station (RAS), a node B (Node B), a base transceiver station (BTS), and an MMR ( Mobile Multihop Relay)-BS, or the like, and may include all or part of functions such as an access point, a radio access station, a node B, a base station for transmission and reception, and an MMR-BS.

Hereinafter, an apparatus and method for avoiding LTE intercell interference according to an embodiment of the present invention will be described with reference to the drawings.

1 is an exemplary diagram for a degree of inter-cell interference according to a general LOS and ISD.

FIG. 1(a) shows a case where the LOS of the radio wave radiated from each cell is short, and FIG. 1(b) shows a case where the LOS of the radio wave radiated from each cell is long.

As can be seen in (a) and (b) of FIG. 1, LTE cells provide interference to each other. When the LOS of radio waves radiated from each cell is long, greater interference is provided to neighboring cells.

Moreover, as can be seen from (b) of FIG. 1, in an environment where a long LOS is guaranteed, the reach of radio waves increases, causing PCI (Physical Cell ID) pollution easily, and forward and reverse quality due to inter-cell interference. Deterioration can occur.

FIG. 2 is a diagram illustrating a cell in which a center frequency is shifted and one sub-carrier of each cell using a conventional center frequency in a frequency domain according to an embodiment of the present invention.

Intra-Frequency cells, which are the same normal cell of the LTE system, use the same center frequency and sub-carrier spacing of 15 kHz, and in this case, each sub-carrier (sub-carrier) in the radio coverage where signals of several cells overlap. -carrier) has the same center frequency.

In LTE OFDMA, since the modulated symbol is transmitted using the center frequency of each sub-carrier, the signal-to-noise ratio (SINR) decreases in the PCI pollution region.

At this time, when using the center frequency shifted by 7.5 kHz from the frequency of the normal cell as shown in FIG. 2, the signal-to-noise ratio (SINR) is improved by avoiding interference occurring in the normal cell. I can make it.

However, since the frequency raster available in LTE is 100 kHz, it is not possible to accurately select the center frequency that fits 7.5 kHz, and the use of a guard band beyond the existing band is related to frequency regulation. Since there may be, it is not desirable to select a shift frequency that is too large.

Considering these points, it can be seen that 200 kHz is the most suitable shift value as shown below.

For Freq _shift =100kHz, 100kHz mod15kHz = 10kHz,

For 200 kHz, 200 kHz mod 15 kHz = 5 kHz,

300kHz mod15kHz = 0kHz for 300kHz,

400kHz mod15kHz = 10kHz for 400kHz.

FIG. 3 shows a difference in signal-to-noise ratio (SINR) due to inter-cell interference in the case of applying a 200 kHz shift and in the case of a normal cell.

When the frequency separation between the two cells is 7.5kHz and 5kHz, the SINR gain is 3dB and 1.6dB, respectively.

At this time, the parameters are shown in Table 1 below.

Parameters Value Freqeuncy 900 MHz Subcarrier Spacing 15 kHz Ant gain of Type 1/ Type 2 OTHAD 14/23 dBi UE Noise Figure 5 dB Reference Signal Power 15 dBm Thermal Noise Density -174 dBm/Hz Antenna Height for OTHAD cell 1650 m Antenna Height for normal cell 50 m

4 is a block diagram of an LTE intercell interference avoiding apparatus according to a preferred embodiment of the present invention.

Referring to FIG. 4, the LTE intercell interference avoiding apparatus according to a preferred embodiment of the present invention includes a cell coverage checker 100, a pollutant cell determiner 200, a target cell selector 300, and a shift frequency selector 400. Includes.

In this configuration, the cell coverage checker 100 checks the cell coverage of the serving cell by using the timing advance statistics included in the RAR (Random Access Response) (hereinafter referred to as RACH MSG2). When the coverage (Cell coverage) exceeds the first threshold (for example, 50 km), a line of sight (LOS) cell is selected.

As such, when the cell coverage checker 100 checks the cell coverage and selects a wide-area line of sight (LOS) cell with a large LOS, the pollutant cell determiner 200 determines whether a PCI pollutant cell is adjacent within the frequency range of the selected cell. If the number of cells (Intra-Frequency neighbor cells) exceeds the second threshold (10 for example), it is determined as a PCI pollution cell.

Then, the target cell selector 300 selects a frequency shift target cell by checking the call cut rate among PCI pollutant cells.

Next, the shift frequency selector 400 selects a shift frequency in consideration of a frequency raster and a guard band usable in LTE.

5 is a flowchart of a method of avoiding LTE intercell interference according to an embodiment of the present invention.

5, in the LTE intercell interference avoidance method according to a preferred embodiment of the present invention, a cell coverage checker checks the cell coverage of a serving cell using TA (Timing Advance) statistics included in RACH MSG2 (S100). When (Cell coverage) exceeds a first threshold, for example, 50 km, a wide area line of sight (LOS) cell is selected (S110).

In addition, the pollutant cell determiner checks the number of intra-frequency neighbor cells of the wide-area line of sight cells selected by the cell coverage checker (S120) and exceeds a second threshold (10 for example). If so, it is determined as a PCI pollution cell (S130).

Thereafter, the target cell selector checks the call disconnection rate among the PCI contaminated cells (S150), and selects a frequency shift target cell (S140).

Next, the shift frequency selector selects a shift frequency in consideration of a frequency raster and a guard band usable in LTE (S160).

6 is a conceptual diagram of a method of avoiding interference between LTE cells according to a preferred embodiment of the present invention.

6A, in the LTE intercell interference avoidance method according to a preferred embodiment of the present invention, the cell coverage checker checks the cell coverage of the serving cell by using Timing Advance (TA) statistics included in the RACH MSG2. When the coverage (Cell coverage) exceeds a first threshold, for example, 50 km, a wide area line of sight (LOS) cell is selected.

And, referring to (b) and (c) of Figure 6, the pollution cell determiner checks the number of intra-frequency neighbor cells of the wide-area line of sight cells selected by the cell coverage checker, and a second threshold ( Threshold) (10 for example) is considered as a PCI pollution cell.

Thereafter, the target cell selector checks the call disconnection rate among the PCI contaminated cells, and selects a frequency shift target cell.

Next, the shift frequency selector selects a shift frequency in consideration of a frequency raster and a guard band usable in LTE.

According to the present invention, the forward and reverse signal-to-noise ratio (SINR) can be improved by shifting the center frequency to minimize inter-cell interference.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

100: cell coverage checker 200: pollution cell determiner
300: target cell selector 400: shift frequency selector

Claims (8)

A cell coverage checker that checks the cell coverage of the serving cell and selects it as a line of sight (LOS) cell when the cell coverage exceeds a first threshold;
A pollution cell determiner for determining whether the wide area line of sight cell selected by the cell coverage checker is a PCI pollution cell;
A target cell selector for selecting a frequency shift target cell by checking a cut rate among PCI pollutant cells determined by the pollutant cell determiner; And
LTE inter-cell interference avoidance including a shift frequency selector for selecting a shift frequency in consideration of a frequency raster and a guard band available in LTE for the frequency shift target cell selected by the target cell selector Device. The method of claim 1,
When the cell coverage checker checks the cell coverage of the serving cell by using timing advance (TA) statistics included in a random access response (RAR) message, and the cell coverage exceeds a first threshold An LTE inter-cell interference avoidance device that is selected as a line of sight (LOS) cell. The method of claim 1,
The pollutant cell determiner exceeds a second threshold by checking the number of intra-frequency neighbor cells of the wide-area line of sight cells selected by the cell coverage checker to determine whether a PCI pollutant cell is present. In the case of a PCI pollution cell (pollution cell), the LTE inter-cell interference avoidance device that determines. The method of claim 1,
The shift frequency selector, LTE inter-cell interference avoidance apparatus for selecting a frequency of 200 kHz as the shift frequency with respect to the center frequency of the frequency shift target cell. (A) the cell coverage checker checks the cell coverage of the serving cell, and selects a line of sight (LOS) cell when the cell coverage exceeds a first threshold;
(B) a pollutant cell determiner determining whether the wide area line of sight cell selected by the cell coverage checker is a PCI pollutant cell;
(C) a target cell selector selecting a frequency shift target cell by checking a call disconnection rate among PCI polluted cells determined by the pollutant cell determiner; And
(D) the shift frequency selector includes the step of selecting a shift frequency in consideration of a frequency raster and a guard band available in LTE for the frequency shift target cell selected by the target cell selector. LTE inter-cell interference avoidance method. The method of claim 5,
Step (A)
(A-1) checking, by the cell coverage checker, the cell coverage of the serving cell by using timing advance (TA) statistics included in a random access response (RAR) message; And
(A-2) LTE inter-cell interference avoidance method comprising the step of selecting a line of sight (LOS) cell when the cell coverage checker has a confirmed cell coverage exceeds a first threshold . The method of claim 5,
Step (B)
(B-1) checking, by the pollutant cell determiner, the number of intra-frequency neighbor cells of the wide-area line of sight cells selected by the cell coverage checker; And
(B-2) LTE inter-cell interference avoidance method comprising the step of determining, as a result of the pollutant cell determiner as a PCI pollution cell (pollution cell) when the number of adjacent cells in the frequency exceeds a second threshold value (Threshold). The method of claim 5,
In the step (D), the shift frequency selector selects a frequency of 200 kHz as the shift frequency with respect to the center frequency of the target cell for frequency shifting.

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