KR20060056212A - Method and system for a wireless communication system using ofdma - Google Patents

Abstract

The present invention relates to a handover method and system in a wireless communication system, and more particularly, to a method and system for stable communication in a wireless communication system.

The present invention provides a method and system that can reduce call cut-off rate, reduce signal-to-noise ratio, improve communication quality, and reduce the effects of interference on adjacent cells in a wireless communication system using an OFDMA scheme.

The system according to the present invention is to provide a system for providing a stable communication function of the terminal in a wireless communication system including an OFDMA terminal and a base station communicating with the terminal. The system sets subchannels in a distributed subcarrier allocation scheme in a specific region configured for allocating to the terminal among downlink and uplink data transmission regions when the terminal and the terminal are located in a specific region. The subchannels are allocated to the terminal within an assignable subchannel ratio among the subchannels set in the region.

OFDMA, Frequency Reuse Factor

Description

TECHNICAL AND SYSTEM FOR A WIRELESS COMMUNICATION SYSTEM USING OFDMA             

1 is a view for explaining a frequency reuse scheme in a cellular mobile communication system using the OFDMA scheme;

2 illustrates an example of configuring one subchannel using a plurality of orthogonal frequencies in different base stations;

3 is a diagram illustrating a configuration of a downlink frame in an OFDMA communication system according to the present invention;

4 is a view for explaining a subchannel allocation method of an uplink in an OFDMA system according to an embodiment of the present invention;

5 is a system configuration diagram for applying the present invention in an OFDMA system;

6 is a control flowchart for subchannel allocation of uplink and downlink from a base station to terminals according to an embodiment of the present invention.

The present invention relates to a wireless communication method and system in a wireless communication system, and more particularly, to a wireless communication method and system in a broadband wireless communication system.

In general, a wireless communication system refers to a method of providing a user to perform communication regardless of a specific place using a terminal. Such a wireless communication system has been developed to accommodate a large number of users using various multiple access schemes. A typical method of the wireless communication system is a code division multiple access (CDMA) scheme. The code division multiple access scheme has been developed to process data at a relatively high speed, beginning with voice communication. As such, the development of code division multiple access is caused by the rapid development of technology with the demand for faster data transmission by users. The code division multiple access method has been commercialized due to the development of technology, and most standards of 3G mobile communication systems have been decided.

However, due to the limited resources used in the code division multiple access scheme, there is a problem that the limit for transmitting data at high speed is reached. Nevertheless, the transmission rate of data required by users continues to increase. Therefore, in the field of wireless communication, various researches and attempts have been made to transmit data at a higher speed.

In one direction of the above-described research, research has been conducted on a method of performing communication using an Orthogonal Frequency Division Multiple Access (hereinafter, referred to as "OFDMA") scheme. In the OFDMA scheme, a plurality of channels are formed using frequencies having orthogonality, and at least one or more channels are allocated to each user to transmit data. Next, the process of communication in the OFDMA scheme will be briefly described.

In the OFDMA scheme, communication uses a scheme of allocating subchannels of uplink and downlink. That is, the communication is performed by dividing the uplink time and the downlink time within a specific time and allocating the channel for each user within the time. In addition, in the cellular mobile communication system based on the OFDMA, two types of operation methods may be largely classified according to an operation method of available frequencies. The available frequency operating method means a method according to a frequency reuse factor. Let's look first at the first and most common way. The first method uses a frequency reuse factor greater than 1, such as 3 or 7. The reason why the frequency reuse coefficient should be used as above will be briefly described with reference to FIG. 1.

1 is a diagram for describing a frequency reuse scheme in a cellular mobile communication system using the OFDMA scheme.

The base stations 100, 110, 120, 130, 140, 150, and 160 form one cell and use different frequencies. That is, one base station uses only 1/3 of all available frequencies. In FIG. 1, each base station uses 1/3 of a carrier index. That is, assuming that all carrier indices are n ₁ + n ₂ + n ₃ , only one region of the carrier indices is configured to be used. Looking at this together with the adjacent base stations (110, 120, 130, 140, 150, 160) of the base station 100, adjacent base stations (110, 120, 130, 140, 150, 160) is the base station 100 Use frequencies of unused carrier index.

As such, by using a frequency having a different carrier index in each base station, interference between each base station can be effectively reduced. As shown in FIG. 1, the frequency reuse factor is 3 when the total usable frequency is divided by 1/3. That is, in the case of configuring a cellular system based on the above method, the frequency reuse coefficient generally has a value greater than three. This is because, as shown in FIG. 1, it is difficult for all base stations to have a theoretical cell structure. Therefore, in general, the frequency reuse coefficient has a value of 3 to 7.

As such, when the frequency reuse factor has a value of 3 to 7, there is a problem that all frequencies cannot be used. The number of carrier indices that can be used in a given base station means the number of users or transmission rate that can be accommodated. Therefore, when the number of carrier indexes decreases, there is a problem in that the number of users that can be accommodated or the transmission rate are limited. On the other hand, when the frequency reuse coefficient has a value of 3 to 7, there is an advantage that the signal-to-noise ratio is excellent even at the cell edge.                         

Next, a method of using the frequency reuse coefficient as 1 will be described. When the frequency reuse factor is 1, each base station in FIG. 1 may use frequencies of all carrier indexes. As described above, using the frequency reuse factor of 1 has an advantage of efficiently using frequency resources. However, when the frequency reuse coefficient is used as 1, the terminals located at the edge of the cell have a disadvantage in that the signal-to-noise ratio is significantly lowered. That is, when the frequency reuse coefficient is used as 1, terminals close to the cell may not be a big problem for communication. However, performance may be deteriorated or communication may not be possible at the cell edge.

Due to this problem, in the conventional OFDMA system, the case where the frequency reuse coefficient has a value of 3 or more has been mostly discussed. However, a lot of discussions have recently been made on how to use the frequency reuse factor as 1 in the IEEE 802.16 standard conference.

On the other hand, the mobile communication system adopts the concept of handover (Handover) to secure the mobility of the terminal. This handover refers to a mobile station (MS) that performs communication so that communication can continue to be maintained even when moving between the base station and the base station. Such handovers can be classified into three types: soft handover, softer handover, and hard handover.

The soft handover refers to a method in which a terminal in communication connects a call to a target target BS through an intermediate process of simultaneously receiving signals of both base stations when moving between base stations. Softer handover is also similar to the soft handover described above, but with the difference that it is within the same base station. That is, softer handover is a method in which a base station provides a soft handover to a terminal when moving in sectors within the base station. Softer handover is therefore possible if the base station is a sector type base station.

Hard handover, on the other hand, when a terminal in communication moves between base stations, it instantaneously disconnects the call of the source BS maintaining the communication and makes a call to the target BS to perform the communication as soon as possible. It means reconnecting in time.

As described above, the current research direction is a method of using a frequency reuse factor of 1. In addition, in the OFDMA system, a hard handover method has been considered during handover. Therefore, when the communication is performed in this manner, terminals located near the edge of the cell have a low signal-to-noise ratio (SINR) during hard handover, and thus suffer from performance degradation or a high call drop rate. It can act as a factor of deterioration in stability. This will be described with reference to FIG. 2.

FIG. 2 illustrates an example of configuring one subchannel using a plurality of orthogonal frequencies in different base stations.

2 illustrates orthogonal frequencies for allocating one subchannel in a cell of a specific base station A and orthogonal frequencies for allocating one subchannel in a cell of another base station B.

The portion indicated in the cell of the base station A shows a plurality of orthogonal frequencies for allocating one subchannel among all orthogonal frequencies. In the OFDMA system, when allocating one subchannel, orthogonal frequencies may be sequentially allocated. However, in general, a plurality of orthogonal frequencies are allocated to one subchannel at random or based on information reported by the UE. Accordingly, orthogonal frequencies form one subchannel in the same manner in the cell of base station B. However, when the subchannels are configured and assigned to the respective terminals as described above, when the two terminals are located in the edge region of the base station and are in close proximity to each other, the two orthogonal frequencies are allocated to each other as shown by reference numerals 210 and 220. . Then, very serious interference occurs between the matching orthogonal frequencies, which may result in deterioration of communication quality or inability to communicate.

In addition, when the power control (Power Control) is used in the above system, the user at the edge of the cell transmits data with high power, thereby causing a large interference signal to users of other cells in the vicinity.

As described above, the biggest problem in the case of hard handover is the low signal-to-interference power ratio (SIR) caused by the interference by the same frequency assigned to the neighbor cell user. The easiest way to solve this problem is to set the frequency reuse factor to a value greater than 1, that is, 3 or 7. Then, as described above, interference from adjacent cells can be reduced. However, this approach requires special cell planning to ensure that adjacent cells or sectors use different frequencies. In addition, frequency efficiency is significantly reduced because the same frequency cannot be used between adjacent cells. Therefore, there is a problem that it acts as a very big burden even when establishing or expanding a base station.

Therefore, there is a need for a system capable of increasing frequency reuse rate without requiring a large cell deployment plan, and a method for performing voice & data communication in such a system is required.

Accordingly, an object of the present invention is to provide a method and system for improving data transmission efficiency in a wireless communication system using an OFDMA scheme.

Another object of the present invention is to provide a method and system for reducing a signal-to-noise ratio during data transmission in a wireless communication system using an OFDMA scheme.

Another object of the present invention is to provide a method and system for improving communication quality in a wireless communication system using an OFDMA scheme.

It is still another object of the present invention to provide a method and system for reducing the influence of interference and the like on adjacent cells in a wireless communication system using the OFDMA scheme.

A method of the present invention for achieving the above object, as a method for providing a handover of the terminal in a base station of a wireless communication system comprising a base station and a base station controller communicating with the terminal and the OFDMA scheme, Setting, by the terminal, subchannels to be allocated to the handover terminal in a distributed subcarrier allocation scheme in a specific subregion allocated to the handover terminal among downlink and uplink data transmission regions; And allocating the subchannels to the handover terminal within an assignable subchannel ratio among subchannels set in an area to be allocated to the handover terminal.

In addition, the method performed in the system according to the present invention comprises the steps of setting the sub-channels in the distributed subcarrier allocation scheme for the remaining areas of the data transmission area for the terminal not located in the handover area of the terminal, and the handover The method may further include allocating the subchannels to a terminal that does not perform the operation.

The system of the present invention for achieving the above objects, the base station of the system for providing a handover of the terminal in a wireless communication system comprising a base station communicating with the terminal and the OFDMA scheme, the base station, the communication with the terminal When the UE is located in the handover area during the execution of the UE, subchannels are set by using a distributed subcarrier allocation scheme in a specific area set for allocating to the handover terminal in each of the downlink and uplink data transmission areas. The subchannels are allocated to a terminal performing the handover within an assignable subchannel ratio among the set subchannels.

Further, the base station sets subchannels in a distributed subcarrier allocation scheme for the remaining areas of the data transmission area for a terminal not located in the handover area among the terminals, and provides the subchannels to the terminal that does not perform the handover. The process of allocating them is further performed.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals have the same reference numerals as much as possible even if displayed on different drawings.

In addition, in the following description, there are many specific details such as specific messages or signals, which are provided to aid the overall understanding of the present invention, and it is understood that the present invention may be practiced without these specific details. It will be self-evident to those of ordinary knowledge. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

The present invention provides a method for smoothly performing hard handoff without cell planning and reducing call blocking rate. The present invention proposes a method for achieving the above objects by using a frequency reuse factor of more than 1 in a part of downlink and uplink data transmission regions.

Before describing the present invention, a system using the OFDMA scheme will be described, and terms used in the present invention will be defined.

The OFDMA communication system allocates resources in units of subchannels, which are sets of specific subcarriers, to each user in uplink and downlink. In this case, there may be various ways of configuring the subchannels. For example, a method of configuring a subchannel in the downlink of the IEEE 802.16 OFDMA scheme includes a method such as PUSC, FUSC, optional-FUSC, AMC permutation, and the like. In the uplink, there are methods such as PUSC, optional-PUSC, and AMC permutation. All other subchannel allocation methods except AMC permutation basically allocate subcarriers randomly distributed in the entire frequency domain to one subchannel to give frequency diversity gain to each user who is allocated the subchannel. In case of uplink, subcarriers are grouped into specific units when subchannels are configured for ease of channel estimation, and then subchannels are configured based on the units. For example, in the uplink of the IEEE 802.16 OFDMA scheme, the PUSC subcarrier allocation scheme divides all subcarriers into tiles consisting of 4 carriers x 3 symbols on the frequency-time axis and randomly selects these tiles to configure a subchannel. In the following description of the subchannel, it will be apparent that the subcarrier can be replaced with a block of the subcarrier.

In addition, a method of dividing all subcarriers into subchannels is performed through a formula determined according to each subchannel configuration method. In this case, the formula includes a parameter for generating different subchannels for each cell. This parameter may have various names, but in the present invention, it is referred to as "cell ID". In addition, subchannel configuration methods as described above will be referred to collectively as "distributed subcarrier allocation method."

FIG. 2 described in the prior art shows an example of arrangement of subcarriers constituting a subchannel allocated by such a distributed subcarrier allocation scheme. In FIG. 2, cells A and B of two base stations have different cell IDs. In addition, as described above with reference to FIG. 2, collisions occur in two subcarriers among subcarriers allocated to one subchannel.

The interference from the neighboring cell is determined by the number of collisions between the subcarriers of the subchannels assigned to a user and the subcarriers of the total subchannels allocated in the neighboring cell from the subchannel point of view. In the distributed subcarrier allocation method, since subcarriers constituting subchannels are randomly distributed in the entire frequency domain, collisions or interferences between subchannels in different cells depend on the number of subchannels allocated regardless of a specific subchannel on average. .

Therefore, in the present invention, when the subchannels are allocated to UEs for handover using a distributed subcarrier allocation method, the amount of interference power from neighbor cells is controlled by limiting the total number of subchannels allocated. This will be described as an example.

Assume that I is the interference power from neighboring cells experienced by each subchannel when all subchannels are allocated. Then, an area to be allocated to UEs to perform hard handover is determined in advance among all subchannels, and the interference power from neighbor cells when only 1 / M is allocated in this area is approximately equal to I in all subchannels. / M Therefore, if hard handover users of neighboring cells are allocated a common region using the distributed subcarrier allocation method as described above and adjust the total number of subchannel allocations in this region, the signal-to-interference noise power ratio for stable hard handover can be achieved. However, even if the channel is allocated in this way, subcarrier overlap may occur. The reason for this is that all subcarriers are allocated using a distributed subcarrier allocation scheme. Therefore, we propose a way to improve this more effectively. The present invention proposes a method for dividing a subcarrier band into several predetermined bands. That is, as shown in FIG. 2B, the entire subcarriers are divided into three predetermined bands. If the subcarrier band is divided into three bands, the subcarrier band may be configured differently from the method of using a subchannel using all subcarriers. First, subcarriers that exist in a handover situation or have a high handover probability or are located at a long distance and are allocated to terminals having a bad channel situation are received from a higher level to a specific region. If the specific area is composed of three as shown in Fig. 2B, it is the same as the case where the three areas use the frequency reuse coefficient of three. Therefore, the subchannel is configured only in the selected area among the three divided areas 230A, 230B, and 230C. In FIG. 2B, it is assumed that the 230A region is selected. When the area 230A is selected as such, the base station combines subchannels in the selected area. That is, as described with reference to FIG. 1, the frequency reuse factor is 3 in the far region and the frequency reuse factor is 1 in the short range. This may be classified by the probability of handover, not divided into the far and near regions, and may be determined in consideration of the situation of the received channel or the reception error rate.

As shown in FIG. 2B, when configuring one channel using subcarriers of the first region 230A, a subchannel may be configured using a distributed subcarrier allocation method within the selected subcarriers. However, if the configuration as shown in Figure 2b it may not necessarily need to use this method. This is because, in an adjacent base station, a subchannel allocated to UEs located in a far-field region or performing a handover or having a high probability of performing a handover on the same subcarrier uses subcarriers of other regions 230B and 230C. Because it transmits. Therefore, one subchannel may be configured by successive subcarriers. However, in the case of using adjacent subcarriers, a restriction due to a channel environment may occur in general, and thus, a distributed subcarrier allocation method may be used as described above. As shown in FIG. 2B, in the case of using the distributed subcarrier allocation method, one subchannel includes 230A-a, 230A-b,... It can be configured as 230A-n.

If the subchannel allocated to the UEs located in the remote area, performing handover, or having a high probability of performing a handover is configured as 1 / n, the fraud-configured channel is also allocated to the remaining terminals. Should be used equally. Therefore, the channel configuration method of the area for transmitting general data is different. This will be described with reference to FIG. 2C.

2C illustrates an example in which one channel is configured using subcarriers for allocating to a general terminal or a terminal in a short range region. As shown in FIG. 2C, subcarriers allocated to a general terminal or a terminal in a short range region configure a subchannel using subcarriers in a region not allocated to the remote region or a terminal performing handover. When a subchannel is configured using the remaining subcarriers, a distributed subcarrier allocation scheme is more preferable. Accordingly, FIG. 2C illustrates a case of configuring a channel using a distributed subcarrier allocation scheme.

As another example, when the number of adjacent base stations is large and the number of terminals performing handover between the base stations is large, the subcarriers may be configured to overlap slightly. This case will be described with reference to FIG. 2D.

As shown in FIG. 2D, assuming that the total number of subcarriers is n + 1, the subcarriers allocated to the first base station are indicated by the reference numeral 240. As shown in FIG. In addition, the subcarriers allocated to the second base station are shown by reference numeral 241, the subcarriers allocated to the third base station are shown by 242, and the subcarriers allocated to the n base station are shown by reference numeral 24n. As shown in FIG. 2D, each subcarrier has a portion overlapping with a predetermined portion. Even though the subcarriers overlap slightly, the number of neighboring base stations is large, so that a large problem does not occur unless a channel having subcarriers in the overlapping region is allocated only to a terminal adjacent to the base station that is actually overlapping. In this configuration, the subcarriers that are not allocated to the handover region, the remote region, or the terminals with high handover possibility configure the subchannels in the same manner as described with reference to FIG. 2C. In addition, when configuring a subchannel using subcarriers allocated to a handover region, a remote region, or a terminal having a high probability of handover, the subchannel may be configured using a distributed subcarrier allocation method. In addition, subchannels may be configured using adjacent subcarriers.

This method will be described in more detail with reference to the accompanying drawings.

3 is a diagram illustrating a configuration of a downlink frame in an OFDMA communication system according to the present invention. Hereinafter, a configuration and allocation method of a downlink frame in an OFDMA communication system according to the present invention will be described in detail.

As shown in FIG. 3, the downlink channel has a preamble 301, MAP information 302, and data transmission regions 310 and 320. The first symbol of the downlink frame usually begins with the preamble 301. Accordingly, each terminal (user) obtains downlink synchronization from the preamble. In addition, MAP information 302 for transmitting uplink and downlink subchannel allocation information to each user equipment is transmitted for several symbols following the preamble. Thereafter, data transmission areas 310 and 320 exist. 3 illustrates an example in which X symbols are set to the handover region subchannels 310 after the MAP information 302 is transmitted. That is, as described above, the present invention includes handover region subchannels 310 for allocating only to terminals located in a handover region, a remote region, or a region having a high handover probability. In the handover region subchannels 310, a frequency reuse factor greater than 1 is used according to the present invention. After the handover area subchannels 310, the mobile station subchannels 310 have general user area subchannels 320 to be allocated to terminals that do not perform handover. The general user region subchannels 320 use a frequency reuse factor of one. Accordingly, the resources of the general user area subchannels 320 constitute subchannels with a frequency reuse factor of 1, and resources are allocated to the respective terminals.                     

On the other hand, since the handover region subchannels 310 have a frequency reuse coefficient greater than 1, there are subchannels 311 used for handover and subchannels 312 not used for handover. . The handover region subchannels 310 allocate only a portion of all assignable subchannels. In addition, in FIG. 3, each of the subchannels may configure a subchannel through the method described with reference to FIGS. 2B and 2D. In addition, one subchannel may be configured using the method described previously.

As such, the ratio R of the number of symbols M of the handover region subchannels 310 and the subchannels 311 that can be allocated to the handover terminal among the handover region subchannels 310 is determined when the system is operated. Can be determined statistically. That is, the ratio is a method used when the method is configured as shown in FIG. 2D. The ratio of the handover user's ratio and the signal and interference noise ratio at the cell edge may be accumulated for a predetermined period and determined using the same. .

In FIG. 3, the general user area subchannels 320 are included after the handover area subchannels 310. However, this order does not matter much if changed. However, if the subchannels of two regions are provided as in the present invention, the object of the present invention can be achieved.

Next, an uplink subchannel allocation method will be described. 4 is a diagram illustrating a method for allocating subchannels of an uplink in an OFDMA system according to an embodiment of the present invention. Hereinafter, an uplink subchannel allocation method in an OFDMA system according to an embodiment of the present invention will be described in detail with reference to FIG. 4.

The uplink includes a control symbol region starting from the first symbol. The control symbol region includes a symbol for ranging, an region for transmitting a response signal of HARQ, and the like. Thereafter, there are general user area subchannels 410 in the area. As described above with reference to FIG. 3, the general user region subchannels 410 are subchannels allocated to users who do not perform a handover with a frequency reuse factor of 1. Accordingly, terminals that do not perform handover are allocated general user area subchannels 410 and transmit on the uplink. On the other hand, the handover region subchannels 420 located after the general user region subchannels 410 do not use the entire subchannel, and only some of them are used as described with reference to FIG. 3.

As such, by allocating some subchannels to the handover terminals, it is possible to reduce the probability of allocating the same frequency resource from an overall perspective. In addition, there is an advantage that the entire band can be utilized without significantly increasing the frequency reuse factor.

5 is a conceptual diagram of an OFDMA system including a base station and a base station controller to which the present invention is applied. Hereinafter, the operation of the base station and the base station controller to which the present invention is applied and the configuration and operation of the entire OFDMA system will be described with reference to FIG. 5.

 The OFDMA system includes base stations 511, 521, and 531 having predetermined regions 510, 520, and 530 that communicate with the terminal. In addition, each of the base stations 511, 521, and 531 is connected to a base station controller 500, and transmits / receives a control signal and serviced data with the base station controller 500. In this case, the control signal may include the above-mentioned restriction channel factors, and the determination of the channel factor will be described below. In addition, the base stations 511, 521, and 531 may deliver statistical values of terminals to be handed over to the base station controller 500.

Accordingly, the base station controller 500 generates the restricted channel factor by using the values according to the present invention, classifies the respective services provided to each terminal, and selects from the upper or lower base stations 511, 521, and 531. Switch incoming traffic. The base station controller 500 performs handover control if necessary. In addition, a packet data service node (PDSN) may be connected to the base station controller 500 to be connected to a wired network. In FIG. 5, the PDNS is not illustrated, but is collectively configured as a wired network 540. The wired network 540 may be connected to a data server 550 providing a data service, and may be connected to a VoIP providing server 560 for providing voice communication.

The data server 550 may be a general Internet server, and may be a server capable of providing various data services such as movies, music, or broadcasting. Of course, it could also be a server for searching and gaming. In addition, the VoIP providing server 560 is a server for converting and providing a voice service into packet data. The VoIP providing server 560 may have a different name or different configuration depending on service providers, but may provide a server capable of transmitting data in an IP type packet. All are generic. It may also include a PTT server that provides a PTT service being developed in the 3G system.                     

Therefore, the base station controller 500 transmits and receives data in accordance with the standard of the wired network 540, and performs a communication function through a communication path with the base station. The base station controller 500 manages a subcarrier set in a specific region of an OFDMA frame. Since the specific subcarrier should be able to be used separately from adjacent base stations for the movement included in a specific area, the subcarrier allocation and management functions can be integrated and performed by the base station controller 500. In the system configuration, when the base station controller 500 includes one or more base stations and different base station controllers are configured, different subcarriers may be allocated to base stations managed by each base station controller through communication between the base station controllers. Adjust it so that it is not shown.

A base station communicates with the base station controller 500. In addition, the base station performs a connection in accordance with the physical terminal and the mobile terminal through a transmission device provided in the base station (not shown in the figure), and transmits and receives data with the terminal. In this case, each base station configures a subchannel according to the method described with reference to FIGS. 2b to 2d when allocating a subchannel to a terminal located in an area of the base station, and allocates the subchannel.

The system management terminal 501 performs a function for system change or state management. In the present invention, the system management terminal 501 is connected to the base station controller 500 and monitors the state of the base station controller 500 and transmits and receives system control commands. The system operator may transmit a subcarrier allocation command through the system management terminal and receive a result of the execution. The wired network 540 is connected to a base station controller or an upper switch (not shown) to perform call setup and data transmission / reception. The upper circuit switch (PSTN) and data communication network (IP network).

FIG. 6 is a control flowchart of generating and transmitting a restricted channel factor to terminals performing handover in a base station controller according to an embodiment of the present invention. Hereinafter, referring to FIG. 6, a control process for generating and transmitting a restricted channel factor to terminals performing a handover in a base station controller will be described in detail with reference to FIG. 6.

The base station controller 500 collects handover data from the base stations in step 610. The collection of such data may be at predetermined intervals or may be required if the base station controller 500 is required. When the handover data is collected from each base station as described above, the process proceeds to step 620 to generate the restricted channel factor for each base station. The limiting channel factor for each base station may be configured according to the number of handover terminals and the amount of data to be transmitted, and is also dependent on the types of neighboring base stations. That is, if the number of neighboring base stations is small and the number of terminals performing handover is small, the limited channel factor has a small value. That is, the frequency reuse coefficient can be used as a small value. However, in the opposite case, a value with a large frequency reuse factor should be used.

After generating the restriction channel factor for each base station as described above, the generated value is transmitted for each base station. Through this, the channel is set in the same manner as in FIGS. 2B to 2D, and the channels to be allocated to the downlink and the uplink can be generated as shown in FIGS. 3 and 4. After that, the base station controller 500 proceeds to step 630 to perform the base station control mode.

Here, the base station control mode includes a process of providing a service through the data server 550 or the VoIP providing server 560 through the wired network 540 of the data provided to the serviced terminal in each base station. In addition, the base station control mode includes a control process for making the most efficient use of the aforementioned frequency resources. The process of performing these two operations together is called a base station control mode.

As described above, the present invention has an advantage of providing various services while efficiently using frequency resources when providing hard handover in an OFDMA communication system.

Claims (2)

In a mobile communication system comprising a plurality of base stations and base station controller, The base station controller transmits and receives control information to and from a plurality of base stations, at least some of the base stations use the same frequency between adjacent base stations, each base station provides a service according to a communicating terminal, and the terminal is located in a specific area. The system of claim 1, wherein the at least one subcarrier allocates another subchannel to reduce collisions between signals transmitted to terminals in the specific region. A method of providing a service in a base station controller of a mobile communication system including a plurality of base stations and a base station controller, Transmitting and receiving control information with a plurality of base stations; And providing a service according to a terminal in which each of the base stations adjacent to each other and using the same frequency are communicating with each other, When providing the above service, Here, the transmission power is distinguished from when the terminal is in a specific region and when it is not, so that at least one subcarrier allocates another subchannel to reduce collisions between signals transmitted to the terminals in the specific region. Said method.

Images