KR101075684B1 - Method for allocating channel in a mobile communication system using ofdma - Google Patents

Abstract

The present invention relates to a method for allocating channels in an OFDMA mobile communication system. The present invention provides a method for reducing inter-cell interference in an OFDMA system and allocating a safety channel / subchannel to an actually required terminal.

In a method for allocating a safety channel in an OFDMA mobile communication system according to an embodiment of the present invention, a base station broadcasts location information and service radius information for notifying its location, and is required to allocate the safety channel from a terminal. Allocating the safety channel according to the presence or absence of channel resources, and the terminal receives and stores the location information and the service radius information of the base station from the base station and measures the distance with the base station during communication with the base station If the probability of leaving the service radius of the base station is higher than the set threshold value, the step of requesting the allocation of the safety channel to the base station.

OFDMA, safety channel, channel assignment.

Description

Channel Allocation Method in Orthogonal Frequency Division Multiple Access Mobile Communication System {METHOD FOR ALLOCATING CHANNEL IN A MOBILE COMMUNICATION SYSTEM USING OFDMA}             

1 is a conceptual diagram between a base station and a terminal for explaining a channel allocation method to which the present invention is applied in an OFDMA system;

2 is a control flowchart for requesting an SA-CH allocation in a terminal of an OFDMA system according to an embodiment of the present invention.

The present invention relates to a channel assignment method in a mobile communication system, and more particularly, to a channel assignment method in an orthogonal frequency division multiple access (OFMDA) mobile communication system.

In general, a mobile communication system is a system that enables communication regardless of a user's location using one of various wireless multiple access schemes. A typical method of such a mobile communication system is a code division multiple access (CDMA) mobile communication system. The code division multiple access mobile communication system is generally focused on voice services, and has been developed to transmit data at various speeds according to system specifications.

However, in the modern society, the speed of development of technology is rapidly increasing, and accordingly, users need to transmit more information quickly. Therefore, many researches and developments have been made to transmit data in a faster and larger amount in the code division multiple access mobile communication system. However, in the code division multiple access scheme, there is a problem that the amount of data that can be transmitted using limited resources does not match the amount of data already required by users. In addition, in the code division multiple access method, since a voice service is basically provided, all resources cannot be allocated to data users.

Due to this, a system for transmitting a larger amount of data faster is required, and a mobile communication system using a broadband wireless communication system based on IEEE 802.16d / e has been proposed. The IEEE 802.16d / e broadband wireless communication system enables high-speed data transmission of up to 30-50 Mbps per sector using time division multiplexing (TDD) OFDMA transmission technology in indoor and outdoor radio environments of 2 to 6 GHz frequency band. . In addition, it is being developed to provide packet-based voice service based on the quality of the existing mobile communication network, and is designed to provide high-speed wireless data service in an extended coverage environment compared to the existing wireless LAN system. Is the next generation wireless access system. The extended area provided by this next generation wireless access system is designed to communicate at 1km / urban, 5km / rural and 60km / hour when moving. In addition, a system has been proposed to use a frequency reuse rate of 1, which is the biggest problem in OFDMA systems.

Next, a mobile communication system of the OFDMA method proposed up to now will be described. In the currently proposed OFDM / TDMA mobile communication system, resource allocation is performed by varying the number of OFDM symbols allocated in each frame according to a transmission rate required by a user. Occupies the entire band alone for a certain period of time, making it inefficient in terms of efficiency for a limited radio frequency. In order to improve this, a method called OFDMA has been proposed. OFDMA can efficiently distribute resources by varying the number of subcarriers allocated according to transmission rates required by each user. Therefore, there is no intra-cell interference because different users are assigned different subcarriers. As such, by ensuring orthogonality among data users in the same cell, multiple users can transmit data for a specific time. This in turn has the effect of causing system capacity increase.

Meanwhile, in order to increase system capacity in a mobile cellular system, it is necessary to minimize interference between cells as well as interference within a cell. However, for efficient frequency use, the OFDMA system aims at a system capable of using a frequency reuse ratio of "1" in multiple cells. Therefore, in order to use the frequency reuse ratio as "1" in an OFDMA system, inter-cell interference may be reduced by using techniques in the form of interference averaging / avoidance. This method can optimize the channel capacity for multiple users, in particular by adaptively determining the frequency bands and number of bits that are good for each user, depending on the channel conditions and transmission rates between each user.

As proposed in the domestic TTA portable Internet standard and IEEE 802.16d / e standard until July 2004, "safe mode operation" is defined to support the above-described method. Such a safe mode operation defines a safety channel left without using a specific subcarrier for each base station and a safety sub-channel used only in its own base station. Now, the safety channel / safety subchannel generation algorithm in the safe mode operation is proposed.

<Safety channel request method prescribed in TTA 2.3GHz mobile Internet standard>

"Based on the reference parameters included in the Uplink Channel Descriptor (UCD) message, the UE transmits a REP-RSP message containing the measurement result to the base station when the quality measurement result for a particular bin exceeds a threshold. To request a safety channel assignment.

Upon receiving the REP-RSP message, the base station determines whether the safety subchannel can be allocated according to the reported channel quality measurement and resource allocation status. If the resource allocation for the safety channel is successful, the allocated safety channel is notified to the terminal through the MAP, and in this case, downlink and uplink subchannels may be allocated together.

When the safety subchannel is allocated, all MAC PDUs for the downlink and uplink should be transmitted through the assigned safety subchannel until the corresponding safety subchannel is released.

If the resource allocation for the safety channel fails, the normal diversity sub-channel is allocated to the channel to be used instead of the safety subchannel. If the channel allocated by the request message is not a safety channel, the terminal considers the request to use the safety channel to be rejected. "

As described above, a safety channel is allocated by performing a safety mode operation. The method for allocating the safety channel / safety subchannel established in the standard is to provide a user at a cell boundary to provide a stable service while minimizing inter-cell interference. However, the assignment of the safety channel as enacted in the standard does not fully satisfy the above purpose. This is because the case described in the above standard may occur in other cases than the case where the inter-cell interference actually occurs. In other words, the terminal mentioned in the TTA 2.3 GHz portable Internet standard and IEEE 802.16d / e, when a quality measurement result for a particular bin exceeds a threshold, sends a safety channel by sending a REP-RSP message containing the measurement result to the base station. "Assignment can be requested." May cause a case in which a user in a cell having a poor channel environment requires a safety channel. If such a case occurs, there is a problem that the service to the user in the cell boundary region that should be allocated as a result of the actual safety channel / subchannel allocation can be disabled.

Accordingly, an object of the present invention is to provide a method for allocating a safety channel so as to reduce intercell interference in an OFDMA system.

Another object of the present invention is to provide a method for allocating a safety channel / subchannel to a terminal actually required in an OFDMA system.

Another object of the present invention is to provide a method for efficiently using safety channel / subchannel resources in an OFDMA system.

It is another object of the present invention to provide a method for efficiently utilizing resources in an OFDMA system.

In a method for allocating a safety channel in an OFDMA mobile communication system according to an embodiment of the present invention, a base station broadcasts location information and service radius information for notifying its location, and is required to allocate the safety channel from a terminal. Allocating the safety channel according to the presence or absence of channel resources, and the terminal receives and stores the location information and the service radius information of the base station from the base station and measures the distance with the base station during communication with the base station If the probability of leaving the service radius of the base station is higher than the set threshold value, the step of requesting the allocation of the safety channel to the base station.

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In addition, the base station allocates the safety channel in an orthogonal frequency division multiple access (OFDMA) mobile communication system which communicates with a plurality of terminals according to the present invention and has a safety channel to be used during handoff. The method comprises the steps of including the latitude and longitude information for indicating the location of the base station and the service radius information in a MAC Management message to configure and broadcast the broadcast information periodically broadcasted by the base station, and Receiving a request for the assignment of the safety channel from the terminal when the probability of leaving the service radius of the base station is higher than a set threshold; and receiving the request for the assignment of the safety channel from the terminal. Allocating the safety channel according to the presence or absence.

In addition, in the mobile communication system of Orthogonal Frequency Division Multiple Access (OFDMA), which communicates with a plurality of terminals according to the present invention and has a safety channel to be used during handoff, the terminal assigns the safety channel. The method may include receiving and storing location information and service radius information of a base station broadcast from a base station, and measuring a distance from the base station when communicating with the base station, thereby leaving the service radius of the base station. If it is higher than the set threshold value, the step of requesting the allocation of the safety channel to the base station.

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DETAILED DESCRIPTION A detailed description of preferred embodiments of the present invention will now be described with reference to the accompanying drawings. It should be noted that reference numerals and like elements among the drawings are denoted by the same reference numerals and symbols as much as possible even though they are shown in different drawings. 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.

1 is a conceptual diagram between a base station and a terminal for explaining a channel allocation method to which the present invention is applied in an OFDMA system. Hereinafter, a concept between a base station and a terminal for explaining a channel allocation method to which the present invention is applied in an OFDMA system will be described.

1 illustrates three different terminals 111, 112, and 113a communicating with two different base stations 110 and 120 and a first base station 110. The base stations 110 and 120 should include the following contents in broadcast information periodically broadcasted by the base station. That is, the present invention means that the following information should be further included in addition to the current standard specification. Information to be included in the broadcast information broadcasted periodically by the base station becomes the following information.

<Fields to be additionally included in broadcast information periodically broadcasted by a base station according to the present invention>

1. Latitude field: Latitude information of the base station (RAS). -90 degrees to +90 degrees

2. Longitude field: Longitude information of the base station (RAS). -180 degrees to +180 degrees

3. Service Radius field (RouteUpdateRadius field): Service radius of the RAS to enable the terminal to update the location.

Of the above fields, the latitude field and the longitude field provide location information of the base station. In addition, the service radius field is information indicating how far the service area of the base station currently communicating with the terminal. As such, the terminal should receive location information and service radius information of the base station from the base stations 110 and 120 and store it in the memory. This information must be updated in at least two cases.

First, the terminal is powered on (power on). When the power is turned on, the terminal needs to acquire the above information while checking which base station it is in and store it in a memory provided therein.

 Secondly, when the terminal moves and the area of the base station is changed, that is, a handoff occurs. In this case, the handoff may be divided into two types. The first case is that the terminal moves without changing the area of the base station is changed. This case is generally referred to as "child handoff" in a mobile communication system. In contrast, this is a case where the area of the base station is changed while actually performing communication. The case where the base station is changed while performing communication is generally called " handoff " in the mobile communication system.

Then, each of the terminals 111, 112, and 113a receives and stores the above information, and then grasps its location to determine the location of the safety channel (safety channel: hereinafter referred to as "SA-CH"). Requires allocation. Therefore, the terminals 111, 112, and 113a according to the present invention need an apparatus capable of determining their location.

Next, the situation illustrated in FIG. 1 will be briefly described. The base stations 110 and 120 illustrated in FIG. 1 are base stations capable of periodically transmitting a broadcast information message according to the present invention. In addition, the terminals 111, 112, and 113a receive and store a broadcast information message periodically broadcasted by the base station according to the present invention in a memory, and calculate a distance between the base station and the terminal.

In addition, it is assumed that the distances between the terminals 111, 112, and 113a shown in FIG. 1 and the base station are different from each other. In addition, it is assumed that channels set to each other are different from each other. It is assumed that the first terminal 111 communicates with the first base station 110 in the state where the channel is the best, and the distance is also the closest. In addition, it is assumed that the second terminal 112 does not have a good channel state with the first base station 110, and the distance is relatively close. That is, the second terminal 112 is not spaced apart from the first base station 110 to perform a handoff. Finally, the third terminal 113a is the terminal farthest from the first base station 110 and is moving to the area of the second base station 120 as shown by reference numeral 130. Accordingly, the third terminal 113a shows a case in which the third terminal 113a soon performs a handoff to communicate with the second base station 120. In FIG. 1, the case where the third terminal communicates with the first base station 110 is indicated by the reference numeral 113a and the case where the second base station 120 communicates with the 113b is illustrated.

This will be described in contrast to the present invention and the prior art. First, the prior art will be described under the above assumption.

As assumed in the foregoing, the second terminal 112 may request allocation of the SA-CH because the channel situation is not good. In this case, the first base station 110 will allocate the SA-CH to the second terminal 112 if the channel resources allow. Thereafter, a handoff situation occurs in the third terminal 113a communicating with the first base station 110. The third terminal 113a then requests the first base station 110 to allocate the SA-CH. However, the SA-CH resource has already been allocated to the second terminal 112. Therefore, if there is no remaining SA-CH resource, the first base station 110 has no resource to allocate to the third terminal 113a which performs the handoff. That is, there is a problem described in the prior art.

Next, a case in which the present invention is applied will be described.

As assumed above, the second terminal 112 has a bad channel situation. However, the second terminal 112 according to the present invention receives and stores broadcast information periodically broadcasted by the base station from the first base station 110, and the distance between the base station and the terminal or the distance between the base station and the terminal from its own location information. Information can be known. Therefore, the second terminal 112 does not require the assignment of the SA-CH to the first base station 110. On the other hand, the third terminal 113a communicating with the first base station 110 also receives and stores broadcast information periodically broadcasted by the base station from the first base station 110, and the distance between the base station and the terminal or its location. The distance information between the base station and the terminal can be known from the information. Therefore, it can be seen that the third terminal 113a is in a handoff situation. Accordingly, the third terminal 113a requests the first base station 110 to allocate the SA-CH. Then, the first base station 110 can perform smooth communication by allocating SA-CH resources to the third terminal 113a.

That is, according to the present invention, the assignment of the safety channel / sub-channel (SA-CH) is assigned at the cell boundary (ie, to the terminal of the handoff area) so that the user of this area avoids interference by other cells and is reliable. You can get services. The terminal may request the safety channel allocation by transmitting a REP-RSP message to the base station.

That is, based on the distance between the terminal and the base station measured by the terminal based on the information broadcast by the system and the reference parameters included in the UCD message provided by the system, the quality measurement result for the particular bin exceeds a threshold. If so, the safety subchannel allocation request is made. To this end, fields must be added on the MAC Management message defined in the existing TTA 2.3GHz portable Internet standard, IEEE 802.16d / e standard. In addition, an operation to be added in the terminal will be described with reference to the control flowchart of FIG. 2 described below.

2 is a control flowchart for requesting an SA-CH allocation in a terminal of an OFDMA system according to an embodiment of the present invention. Hereinafter, a control process for an allocation request for SA-CH in a terminal according to the present invention will be described in detail with reference to FIG. 2.

In step 200, the terminal receives and stores broadcast information periodically broadcasted by the base station. The time point at which the base station periodically receives and stores broadcast information is the same as described above. That is, when the terminal is powered on or when the handoff. After the base station periodically receives and stores broadcast information, the terminal proceeds to step 210 to check whether communication is required. If communication result of the check of step 210 is required, the process proceeds to step 220 and maintains the standby state not shown in FIG. The standby state is generally a state waiting for the start of communication or waiting for a request for a specific function added to the terminal. The waiting for the communication includes both incoming and outgoing calls.

When the communication proceeds to step 220, that is, when the communication is requested, the terminal sets a timer to perform the distance measurement and measures the distance between the base station and the terminal. After the terminal sets a timer and calculates the distance between the base station and the terminal, the terminal proceeds to step 230 and checks whether the terminal is in a handoff state by using information included in the broadcast information periodically broadcasted by the base station. do. That is, it is checked whether the allocation of SA-CH is necessary.

Then, a case in which SA-CH allocation is required will be described in more detail. The terminal grasps the location information of the base station by using the broadcast information broadcasted periodically by the base station. In addition, the terminal according to the present invention may obtain the distance information with the base station from its location information or may know the distance information by using a specific communication method with the base station. As such, when the distance information with the base station is obtained, the service radius information of the base station may be obtained from the broadcast information periodically broadcasted by the base station. Therefore, it is to check whether the distance between the base station and the terminal is located in the change of the service radius.

In general, the base stations do not all have the same service radius. Therefore, the base station may include a threshold to perform the handoff in the above-described service radius information to transmit. In this case, the terminal may use only the distance between the base station and the terminal and broadcast information periodically broadcasted by the stored base station when checking whether the SA-CH is necessary. However, when the base station transmits a signal including a threshold to perform handoff, there is a problem in that the reception characteristics and channel environment of each terminal cannot be sufficiently reflected. Therefore, the terminals may use a predetermined threshold such as whether the distance from the base station corresponds to 90% or 95% of the service radius included in the broadcast information message periodically broadcast by the base station, or is out of the service radius or located outside the service radius. Can be used to set the method. Alternatively, the strength of the received signal may be used. Since the method using the strength of the received signal belongs to the general handoff method, it will not be described in detail here. In the present invention, any of the above three methods may be used.

In step 230, the UE checks whether SA-CH allocation is necessary by using one of the above-described methods, or two or all three methods. If it is necessary to allocate the SA-CH, the procedure proceeds to step 240 to generate a REP-RSP message, request the SA-CH, and perform communication through the currently allocated channel. However, if the allocation of the SA-CH is not necessary, the terminal proceeds to step 260 to perform communication using a channel allocated from the base station. In FIG. 2, the process of channel allocation is not illustrated and will not be described. This is because the allocation of these channels is a general process.

The terminal performs step 240 or step 260 and checks whether the distance measuring time of step 250 has arrived. In this way, the inspection whether the distance measurement time has arrived is when the timer time set in step 220 has elapsed. When the distance measurement time arrives as a result of the test, the terminal proceeds to step 220 and performs operations 220 to below. On the other hand, if the distance measurement time has not arrived, the process proceeds to step 260 to continue communication with the current base station through the assigned channel.

As described above, the present invention can prevent unnecessary allocation of SA-CH in the OFDMA system, so that the use of the channel can be more smoothly performed.

Claims (10)

A method for allocating a safety channel in an orthogonal frequency division multiple access (OFDMA) mobile communication system, The base station broadcasts the location information and service radius information for indicating its location, and when the allocation of the safety channel from the terminal is required to allocate the safety channel according to the presence or absence of channel resources, The terminal receives and stores the location information and the service radius information of the base station from the base station and when the probability of leaving the service radius of the base station by measuring the distance with the base station during communication with the base station is higher than the set threshold value And requesting assignment of the safety channel to the base station. The method of claim 1, wherein the location information and service radius information of the base station, The safety channel allocation method, characterized in that it is periodically broadcast from the base station included in the MAC Management message. delete The method of claim 1, wherein the distance measurement with the base station, The safety channel allocation method, characterized in that made based on the location information of the terminal and the location information of the base station. The method of claim 1, wherein the distance measurement with the base station during the communication, Safety channel assignment method characterized in that the set period. A method for allocating a safety channel by a base station in an orthogonal frequency division multiple access (OFDMA) mobile communication system that communicates with a plurality of terminals and has a safety channel to use during handoff, Including the latitude and longitude information and the service radius information for indicating the location of the base station in a MAC management message and configuring and broadcasting the broadcast information periodically broadcasted by the base station; Receiving a request for allocation of the safety channel from the terminal when the terminal communicating with the base station has a probability that the terminal deviates from the service radius of the base station is higher than a predetermined threshold value; And allocating the safety channel according to the presence or absence of a channel resource when a request for the allocation of the safety channel is received. The method of claim 6, wherein the latitude and longitude information and the broadcast of the service radius information, Safety channel assignment method characterized in that the set period. Method for requesting allocation of the safety channel in an orthogonal frequency division multiple access (OFDMA) mobile communication system that communicates with a plurality of terminals and has a safety channel for handoff among the terminals To Receiving and storing location information and service radius information of the base station broadcast from the base station; Measuring a distance from the base station when communicating with the base station and requesting allocation of the safety channel to the base station when the probability of leaving the service radius of the base station is higher than a predetermined threshold value. How to assign safety channels. The method of claim 8, wherein the distance measurement with the base station, The safety channel allocation method, characterized in that made based on the location information of the terminal and the location information of the base station. The method of claim 8, wherein the distance measurement with the base station in the communication, Safety channel assignment method characterized in that the set period.

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