KR101265304B1 - method for changing cell coverage in mobile communication system - Google Patents

Abstract

The present invention relates to a method of changing cell coverage in a mobile communication system.

In a mobile communication system, the radius of a given cell is checked. The size of the cyclic prefix is changed in a data symbol composed of a cyclic prefix (CP) to avoid interference between the data interval and the symbol according to the identified cell radius. In particular, the smaller the radius of the cell, the smaller the cyclic prefix size, and the larger the radius of the cell, the larger the cyclic prefix size.

Therefore, by dynamically allocating the size of the cyclic prefix according to the cell environment, it is possible to obtain an effect such as cell area expansion while minimizing additional hardware change.

Circulating prefix, cell coverage, cell radius

Description

Method for changing cell coverage in mobile communication system

1 is a diagram illustrating a network environment of a mobile communication system according to an exemplary embodiment of the present invention.

2 is a frame structure diagram according to an embodiment of the present invention.

3 is a flowchart illustrating a cell coverage change method according to an embodiment of the present invention.

4 is a structural diagram of a transmitter according to an embodiment of the present invention.

The present invention relates to a mobile communication system, and more particularly, to a method of changing cell coverage of a base station in a mobile communication system.

In general, an area serviced by one base station in a mobile communication system is called a cell, and when a cell is divided into a plurality of areas, each area is called a sector. In designing the cell of the base station, the process of optimizing the location and the number of the base station is very important in terms of cost and radio wave use. The basis of this is the cell coverage occupied by each base station. Each cell may be classified into a picocell, a microcell, a macrocell, and the like according to its size.

In an orthogonal frequency division multiplexing (OFDM) system such as a mobile Internet system, a cyclic prefix (CP: Cyclic Prefix) considering a frame radius, transmission delay, and multipath delay in consideration of the maximum cell rate Set the system parameters such as the length of). In mobile Internet systems, the cell radius is fixed at a maximum of 1 km.

However, a change such as dividing a cell according to a predetermined variable such as the distribution, density, and traffic volume of a user using the cell should be made. When using a fixed system parameter, the cell size is fixed regardless of the change of the variable. There is this. In this case, the efficiency is reduced in the installation and operation of the system.

Conventional techniques for extending cell coverage include "Orthogonal Frequency Division Multiple Communication Methods and Apparatuses Adaptive to Channel Characteristics" described in Korean Patent Application Publication No. 10-2004-0011653. This technique discloses a method of expanding or reducing the area of a cell by adjusting the number of carriers of the IFFT / FFT to various numbers, for example, 2048, 1024, 512, and the like. However, as the number of carriers of the IFFT / FFT in the OFDM system is adjusted, a change in the frequency band is involved, and as a result, the structure and operation control of the demodulator for data demodulation in the mobile terminal are complicated. In addition, it is not applicable to a system in which the number of carriers of the IFFT / FFT is fixed.

Therefore, the present invention is to provide a method of changing the coverage of a cell according to a cell environment while maintaining a constant number of carriers in a mobile communication system.

According to another aspect of the present invention, there is provided a method of changing a cell coverage in a mobile communication system, the method comprising: checking a radius of a cell; And changing the size of the cyclic prefix in a data symbol consisting of a cyclic prefix to avoid interference between the data interval and the symbol, in accordance with the identified cell radius.

In the present invention having such characteristics, the smaller the radius of the cell, the smaller the cyclic prefix size, and the larger the radius of the cell, the larger the cyclic prefix size. In this case, the size of the cyclic prefix may be a cyclic prefix time indicating a temporal ratio of the cyclic prefix size to the data interval. In addition, the method of changing the cell coverage of the present invention may be performed in a control station controlling base stations in a mobile communication system.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

In addition, when a part is said to "include" a certain component, this means that it may further include other components, except to exclude other components unless otherwise stated.

1 is a diagram schematically illustrating a structure of a mobile communication system according to an exemplary embodiment of the present invention.

1 is a view illustrating a structure of a mobile communication system according to an exemplary embodiment of the present invention. Basically, a subscriber station 200 is connected to a base station 100, 100 ′, and the base station 100, 100 ′ is a control station 300. It is connected to other network through. In a mobile communication system such as a wireless portable Internet, the subscriber station 200 and the base stations 100 and 100 ′ may communicate by using orthogonal frequency division multiple access (OFDMA). It is not limited to.

In an embodiment of the present invention, the size of a cyclic prefix (CP) is set as a system parameter according to the size of cell coverage while maintaining a fixed number of carriers. In this case, a variable representing the size of the cell coverage, that is, the cyclic prefix size that is changed according to the cell radius, is used, but the cyclic prefix time (CP_IND) representing the temporal ratio of the cyclic prefix size to the data interval is used. Or, for example, the cyclic prefix size itself may be used.

The setting of the system parameter is performed at the control station managing the mobile communication system. The system parameters set at the control station are transferred to the apparatus for performing demodulation of the base station and used for data modulation and demodulation. The control station also transmits system parameters to all subscriber stations 200 in the base station via the broadcast channel. Therefore, the subscriber station 200 uses the received system parameter as a parameter for data modulation and demodulation.

2 shows a frame structure according to an embodiment of the present invention.

A frame according to an embodiment of the present invention includes a preamble symbol, a control symbol, and a data symbol for channel estimation, as shown in FIG. 2. In the TDD system, a TTG (Transmit / Receive Transition Gap) and a RTG (Receive / Transmit Transition Gap) are included for switching from the forward link to the reverse link and from the reverse link to the forward link.

In order for various cell coverage to coexist, the preamble symbol and the control symbol must have a common symbol size. One data symbol consists of a cyclic prefix to avoid interference between data intervals and symbols. In FIG. 2, Example 1) shows a case in which the cyclic prefix is set to 12.5usec according to cell coverage, and Example 2) shows a case in which the cyclic prefix is set to 25.0usec in the embodiment of the present invention. This cyclic prefix is a minimum section for preventing the previous symbol signal from affecting the next symbol due to transmission delay and multipath delay.

The cyclic prefix is determined in the following manner.

As described above, the cyclic prefix is determined by the sum of the maximum round trip delay time (RTDelay) according to the cell radius and the maximum multipath delay time (MPDelay) that can be generated by the multipath.

Currently, the wireless portable Internet system has 1024 carriers, the cell radius is set to 1Km, and the maximum transmission rate of the system is set to about 30Mbps in the 10MHz band. Table 1 is an exemplary diagram showing values of parameters used in the wireless portable Internet system.

According to these variables, the maximum round trip delay time is 6.6 usec, and the multipath delay time is set to about 6usec. According to Equation 1 above, the cyclic prefix is 12.8usec. In this case, 12.8usec, which is one eighth of the data interval of about 102.4usec, is allocated as a cyclic prefix.

In the embodiment of the present invention, the maximum round trip delay time and the maximum multipath delay time vary according to the detected cell radius, and as a result, the cyclic prefix size varies. Table 2 below shows an example of a cyclic prefix that is set differently according to a cell size in an embodiment of the present invention, and particularly shows a cyclic prefix time CP_IND set differently according to a cell radius.

In the embodiment of the present invention, the length of the entire symbol is changed according to the cyclic prefix time, that is, the cyclic prefix size, so that the TTG and RTG values are also set separately according to the changed length, so that the forward link and the reverse link overlap. The synchronization of the uplink and the synchronization of the downlink are aligned so that there is no interval.

Next, a method of changing cell coverage according to an embodiment of the present invention will be described.

3 is a flowchart illustrating a cell coverage change method according to an embodiment of the present invention. In the embodiment of the present invention, the cell coverage change is performed by the control station 300, but is not necessarily limited thereto.

In order to set system parameters for all cells or specific cells in the waiting process, as shown in FIG. 3, first, reference parameters that are most preferred or most commonly used in the system area are set. Most base stations set system parameters as reference parameters (S100 to S110). For example, the radius of a cell is set to a reference radius (R _REF , for example 1 Km), the reference data symbol (DataSYM _REF , for example 100usec), the reference cyclic prefix size (CP _REF , for example 12.5usec). ), The reference parameters of the reference cyclic prefix time CP_IND _REF , for example 1/8, are set as system parameters.

However, if cell coverage needs to be expanded or cell coverage needs to be reduced, the following process is performed.

First, make the radius of the cell (R _new) (S120). And compared to the number of the set range is set to a radius (R _new) of the identified cell is determined are included in a range, and rotate at a set range including the radius (R _new) of the identified cells according to the determination result in contact Determine tofu time. In an embodiment of the present invention, as the radius of the cell becomes narrower, the cyclic prefix time is set to be shorter than the reference cyclic prefix time, and as the radius of the cell is wider, the cyclic prefix time is set to be longer than the cyclic prefix time.

Specifically, the radius R _new of the identified cell is included in the first setting range (where the first setting range is less than 1/4 × R _REF of the reference cell radius, for example, 0.25 km or less). In the case of S130, the cyclic prefix time CP_IND _NEW of the cell radius R _new is set to 1/4 times CP_IND _REFE of the reference cyclic prefix time (S140).

In addition, the radius R _new of the identified cell represents a second setting range (where the second setting range is larger than 1/4 × R _REF of the reference cell radius and less than 1/2 × R _REF , for example, 0.25 km). Larger than 0.5 km or less) (S150), the cyclic prefix time CP_IND _NEW of the cell radius R _new is 1/2 times the reference cyclic prefix time (1/4 × CP_IND _REFE ). Set to (S160).

Also, the radius R _new of the identified cell represents a third setting range (where the third setting range is larger than 1/2 × R _REF of the reference cell radius and less than or equal to R _REF , for example, greater than 0.5 km and less than 1 km). Case), the cyclic prefix time CP_IND _NEW of the cell radius R _new is set as the reference cyclic prefix time CP_IND _REFE (S180).

In addition, the radius (R _new) of the identified cell, the fourth set range including (where the fourth setting range is based shows a cell radius R _REF, if larger than 2 × R _REF, for example, if large or less 2km than 1km) In step S190, the cyclic prefix time CP_IND _NEW of the cell radius R _new is set to twice the reference cyclic prefix time (2 × CP_IND _REFE ) (S200).

In addition, when the confirmed radius of the cell (R _new ) is included in the fifth set range (where the fifth set range is larger than the reference cell radius 2 × R _REF , for example, larger than 2 km) (S210). The cyclic prefix time CP_IND _NEW of the cell radius R _new is set to four times the reference cyclic prefix time (4 × CP_IND _REFE ) (S220).

As described above, the control station 300 determines the cyclic prefix time differently according to the radius of the cell, and the system parameters including the determined cyclic prefix time are transmitted to the base station 100 (S230).

Where lKm is the maximum radius and 0,5km is the minimum radius. However, it is not limited thereto.

Meanwhile, in the above embodiment, the cyclic prefix time is directly changed according to the cell radius, but, for example, the cyclic prefix size is set differently according to the cell radius, and the cyclic prefix size for the data interval according to the set cyclic prefix size. You can change the cyclic prefix time that represents the ratio of.

Subsequently, the base station 100 processes a signal to be transmitted or a received signal according to a system parameter, and also transmits a message including a system parameter to all subscriber stations in the base station through a broadcast channel. Accordingly, the subscriber station operates the modulation / demodulation device based on the transmitted system parameter to process the transmitted and received signal. This allows all systems to operate with the same parameters.

Meanwhile, the transmission apparatus according to an embodiment of the present invention modulates a signal according to a system parameter including a cyclic prefix size set according to the cell coverage change method as described above.

4 shows a schematic structure of a transmitting device in a mobile communication system according to an embodiment of the present invention. In particular, FIG. 4 illustrates an element mainly performing a modulation function for data transmission in a transmission apparatus.

As shown in FIG. 4, a transmission apparatus according to an embodiment of the present invention includes a data receiver 10 for receiving and storing a complex number of data, and an IFFT unit 20 for outputting the stored data by performing inverse fast fourier transform (IFFT) processing. ), A cyclic prefix storage unit 30, a modulation control unit 40, a signal converter (D / A, 50) and a radio signal processor (60).

The data receiving unit 10 receives and stores a predetermined number (eg, 1024) of complex numbers in symbol units, and the IFFT unit 20 performs IFFT processing on the stored data. The radio signal processor 60 processes the symbol signal into a radio signal and transmits the symbol signal over the radio section.

The modulation control unit 40 controls data modulation based on the system parameters as described above provided from the control station 300. Specifically, after the completion of IFFT, one symbol is formed by adding a cyclic prefix for maintaining orthogonality to the IFFT processed data while preventing interference between symbols. For this purpose, the modulation control unit 40 stores data corresponding to the size of the cyclic prefix included in the system parameter (for example, the cyclic prefix time, which has a value dynamically changed according to the cell radius) in the second half of the IFFT processed data. Stored in the CP storage unit 30, or immediately transmitted to the signal conversion unit 40 sequentially first. After the data transfer corresponding to the cyclic prefix size is completed, the IFFT-processed data is transferred to the signal converter 40 sequentially from the first half to the second half, thereby forming one symbol. Accordingly, a cyclic prefix consisting of data corresponding to the size of the cyclic prefix is formed, followed by a symbol having a form in which data is arranged.

The above-described embodiments of the present invention are not only implemented through the apparatus and the method, but may also be implemented through a program or a recording medium on which the program is recorded to realize a function corresponding to the configuration of the embodiments of the present invention. From the description of the embodiments described above can be easily implemented by those skilled in the art.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

According to the embodiment of the present invention described above, it is possible to easily change the cell coverage in the mobile communication system. In particular, it is possible to extend or reduce the coverage of the cell according to the cell environment while keeping the number of carriers constant.

Claims (8)

In a method of changing cell coverage in a mobile communication system, Checking the radius of the cell; And Changing the size of the cyclic prefix in a data symbol consisting of a cyclic prefix for avoiding interference between data intervals and symbols according to the identified cell radius Including, The step of changing the size of the cyclic prefix changes the cyclic prefix time representing the temporal ratio of the cyclic prefix size and the data interval according to the radius of the cell. The method of claim 1 Setting a system parameter including a size of the modified cyclic prefix; And Transferring the set system parameter to a corresponding base station in a mobile communication system. Further comprising the devices of the base station operating in accordance with the system parameters. The method according to claim 2, wherein And the base station transmits a message including the set system parameter to subscriber stations and the devices of the subscriber station operate according to the system parameters, so that the base station and the terminals use the same system parameter. The method according to any one of claims 1 to 3 And narrowing the cyclic prefix size as the radius of the cell decreases, and setting the cyclic prefix size as the radius of the cell increases. The method according to any one of claims 1 to 3 One frame including the data symbol includes a transmit / receive transition gap (TGT) and a receive / transmit transition gap (RTG) for switching from a forward link to a reverse link and a reverse link to a forward link. And the values of the TTG and RTG are changed according to the radius of the cell. delete The method of claim 1 Changing the size of the cyclic prefix Identifying a range that includes the radius of the cell; Setting a cyclic prefix time of the radius of the cell as a reference cyclic prefix time if the radius of the cell is within the maximum and minimum radius set by the system; If the radius of the cell exceeds the maximum radius set by the system, setting the cyclic prefix time of the radius of the cell as an incremental multiple of the reference cyclic prefix time to increase the cyclic prefix time; And If the radius of the cell is smaller than the minimum radius set by the system, setting the cyclic prefix time of the radius of the cell as a reduced multiple of the reference cyclic prefix time, thereby reducing the cyclic prefix time. Cell coverage change method comprising a. The method according to any one of claims 1 to 3 And the cell coverage changing method is performed at a control station controlling base stations.

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