System and method of assigning frequency sources based on multiple frequency reuse ratio in cellular communication system

The present invention relates to a cellular communication system, and more particularly to a system and method for allocating frequency resources based on a multiple frequency reuse rate in a cellular communication system using the orthogonal frequency division multiple connection method.

In general, in a cellular communication system, the same frequency resource can be used in two spatially separated regions in order to effectively use the limited frequency resource. Here, the concept of frequency reuse will be described with reference to FIG. FIG. 1 is a diagram schematically showing the concept of frequency reuse in a conventional cellular communication system.

Referring to FIG. 1, the frequency resource F1 used in the first cell 100 having a radius R is used in a second cell 150 having a radius R separated by D from the center of the first cell 100. Can be done. This is called "frequency reuse".

On the other hand, the frequency reuse factor K is obtained when the same frequency resource, that is, the frequency band is reused in units of K cells. As the frequency reuse rate increases, so does the distance D between frequency reuse cells that use the same frequency resource. Also, since propagation is attenuated in proportion to the propagation distance, the amount of interference due to the use of the same frequency resource decreases as the frequency reuse rate increases. On the other hand, the amount of frequency that can be used in one cell is obtained by dividing the entire frequency band by the frequency reuse rate K, and as the frequency reuse rate increases, the efficiency of the entire system decreases. Will be done.

The frequency resource allocation operation according to the frequency reuse rate K will be described with reference to FIGS. 2A to 2F. FIG. 2A is a diagram schematically showing a frequency resource allocation operation when the frequency reuse rate K is 3 (K = 3). Referring to FIG. 2A, when the frequency reuse rate K is 3, 1/3 of the entire frequency band is allocated to each of the three cells. FIG. 2B is a diagram schematically showing a frequency resource allocation operation when the frequency reuse rate K is 4. As shown in FIG. 2B, when the frequency reuse rate K is 4, 1/4 of the entire frequency band is allocated to each of the four cells.

FIG. 2C is a diagram schematically showing a frequency resource allocation operation when the frequency reuse rate K is 7. Referring to FIG. 2C, when the frequency reuse rate K is 7, 1/7 of the entire frequency band is allocated to each of the 7 cells.

FIG. 2D is a diagram schematically showing the frequency resource allocation operation when the frequency reuse rate K is 3/9 (K = 3/9). With reference to Fig. 2D, when the frequency reuse rate K is 3/9, the entire frequency band should be divided by 1/3 in units of 3 cells within a total of 9 cells. As a result, the frequency reuse rate K = 3/9 is applied to each of the above nine cells.

FIG. 2E is a diagram schematically showing the frequency resource allocation operation when the frequency reuse rate K is 4/12 (K = 4/12). With reference to Fig. 2E, when the frequency reuse rate K = 4/12, the entire frequency band should be divided into 1/4 in units of 3 cells within a total of 12 cells. As a result, the frequency reuse rate K = 4/12 is applied to each of the above 12 cells.

FIG. 2F is a diagram schematically showing the frequency resource allocation operation when the frequency reuse rate K is 7/21 (K = 7/21). With reference to Fig. 2F, when the frequency reuse rate K is 7/21, the entire frequency band should be divided by 1/7 in units of 3 cells within a total of 21 cells. As a result, the frequency reuse rate K = 7/21 is applied to each of the above 21 cells.

On the other hand, in the case of an analog cellular communication system, a minimum signal-to-noise ratio (hereinafter referred to as'SNR') is required to create a wireless voice communication line, and in order to satisfy the above SNR. Determines the minimum distance between cells. Therefore, the frequency reuse rate is also determined based on the above SNR.

In contrast, for digital cellular communication systems, the minimum signal-to-noise ratio has a variety of values, based on the error correction coding rate, modulation scheme, and transmission scheme applied to the radio line. In particular, Code Division Multiple Access (hereinafter referred to as'CDMA') communication systems re-frequency all cells in consideration of minimum SNR, overall system capacity, and ease of network design. Apply usage rate "1". Since the CDMA communication system uses the same frequency band for all cells, a code spreading / despreading process is used to separate each cell. In this way, the interfering components of adjacent cells are averaged so that the data in the current service cell can be separated from the data in other cells.

The frequency reuse rate is also an important design factor in wireless packet cellular communication systems that use the Orthogonal Frequency Division Multiple Access (hereinafter referred to as'OFDMA') method. As described above, when the frequency reuse rate K is 1, the capacity of the entire system and the design of the network become easy. Here, referring to FIG. 3, in the cellular communication system having the frequency reuse rate 1, the carrier to interference / noise ratio of the downlink signal (hereinafter referred to as'CINR'). Will be described.

FIG. 3 is a diagram schematically showing a downlink CINR in a cellular communication system using a frequency reuse rate 1. As shown in FIG. 3, the cell center region 301 adjacent to the base station has little effect on the strength of the downlink signal, i.e., the strength of the interference signal whose CINR has the same frequency band from the adjacent cell. It does not receive and shows a relatively large CINR. However, the cell boundary region 303, which is separated from the base station, exhibits a relatively small CINR because the influence of interference signals having the same frequency band from adjacent cells is very large.

If the Subscriber station (SS) is located in the cell boundary region 303, the SS will be normal from the Base station (BS) if the cellular communication system provides a very low error correction coding rate and modulation scheme. Even if the data packet can be received in the cell boundary region 303, the frequency efficiency of the SS in the cell boundary region 303 is reduced.

In order to solve such a problem, the frequency reuse rate K is set to K> 1. Thus, even when the frequency reuse rate K is set to K> 1, the signal is attenuated in proportion to the propagation distance, and as a result, the downlink CINR becomes higher toward the cell boundary region 303. Will be reduced. However, since the interference component generated in the same frequency band of the adjacent cell is very small, the frequency reuse rate K is K> 1 as compared with the downlink CINR when the frequency reuse rate is the same as 1. The downlink CINR is relatively large when set to. This will be described with reference to FIG.

FIG. 4 follows the distance from the base station when the frequency reuse rate is 1 (K = 1) and when the frequency reuse rate exceeds 1 (K> 1) in a general cellular communication system. It is a graph which shows the relationship of CINR. As shown in FIG. 4, as the frequency reuse rate increases, the frequency efficiency in the cell boundary region can be increased. However, since each cell uses 1 / K of the entire frequency band, the capacity of the entire system is reduced compared to that of a system using frequency reuse rate '1'.

<p><patcit num="1"><text>Special Table 2003-50095 No. 1</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 2003-018091</text></patcit><patcit num="3"><text>Japanese Patent Application Laid-Open No. 5-292010</text></patcit><patcit num="4"><text>Japanese Unexamined Patent Publication No. 10-108250</text></patcit><patcit num="5"><text>Japanese Unexamined Patent Publication No. 2001-238252</text></patcit><patcit num="6"><text>Japanese Unexamined Patent Publication No. 2002-320257</text></patcit></p>

<p> In view of the above background, an object of the present invention is to provide a system and a method for allocating frequency resources based on a multiple frequency reuse rate in an OFDMA cellular communication system.</p><p> Another object of the present invention is to apply a multiple frequency reuse rate corresponding to the channel state of the terminal in an OFDMA cellular communication system to allocate frequency resources that can increase the system capacity and increase the reliability of the system. To provide systems and methods.</p>

<p> In order to achieve such an object, according to the first aspect of the present invention, the method in which the transmitter of the cellular communication system allocates frequency resources is a preset time interval of at least two or more sub time intervals. It is characterized by including a step of dividing into the above-mentioned frequency resources and a step of forming the above-mentioned frequency resources by applying different frequency reuse rates to the above-mentioned sub-time intervals.</p><p> According to the second aspect of the present invention, the method in which the transmitter of the cellular communication system allocates frequency resources includes a step of dividing the entire subcarrier of the cellular communication system into at least two or more groups and each of the above groups. Is divided into at least two or more subgroups according to the number of frequency reuse rates applied to the cellular communication system, and the subgroups are divided into subgroup sets corresponding to the frequency reuse rates. It is characterized by including a step of selecting a preset number of subcarriers from each of the subgroups of the subgroup set to form the frequency resource.</p><p> According to the third viewpoint of the present invention, the system for allocating frequency resources in the cellular communication system divides a preset time interval into at least two or more sub time intervals, and the frequencies differ from each other in the sub time intervals. It is characterized by including a transmitter that constitutes a frequency resource by applying a reuse rate.</p><p> According to a fourth aspect of the present invention, in a cellular communication system, a system that allocates frequency resources divides the entire subcarrier of the cellular communication system into at least two or more groups, and each of the groups is divided into the cellular communication. Divide into at least two or more subgroups according to the number of frequency reuse rates applied to the system, and divide the subgroups into subgroup sets corresponding to each of the frequency reuse rates. It is characterized in that a transmitter constituting the above frequency resource is provided by selecting a preset number of subcarriers from each subgroup of the subgroup set.</p><p> According to the fifth viewpoint of the present invention, the cell / sector is provided for a frequency reuse rate K defined as one frequency band being used repeatedly for each K cell / sector. In each of the base stations, the method of reusing the frequency within the predetermined time interval on the time region is to set the frequency reuse rate 1 in the first time interval which is a part of the preset time interval. It is characterized by including a step to be used and a step to use the frequency reuse rate K in the second time interval, which is the remaining part of the preset time interval.</p>

<p> According to the present invention, in the OFDMA cellular communication system, by allocating frequency resources based on the multiple frequency reuse rate, it is possible to prevent the phenomenon that the CINR is lowered in the cell boundary region and improve the system performance. Further, according to the present invention, there is an advantage that the system capacity can be increased and the reliability of the service can be improved by applying the multiple frequency reuse rate according to the channel state of the terminal.</p>

<figref num="1">It is a figure which shows schematic the concept of frequency reuse in the conventional cellular communication system.</figref><figref num="2A">It is a figure which shows schematic the frequency resource allocation operation when the frequency reuse rate K is 3.</figref><figref num="2B">It is a figure which shows schematic the frequency resource allocation operation when the frequency reuse rate K is 4.</figref><figref num="2C">It is a figure which shows schematic the frequency resource allocation operation when the frequency reuse rate K is 7.</figref><figref num="2D">It is a figure which shows schematic the frequency resource allocation operation when the frequency reuse rate K is 3/9.</figref><figref num="2E">It is a figure which shows schematic the frequency resource allocation operation when the frequency reuse rate K is 4/12.</figref><figref num="2F">The frequency resource allocation operation when the frequency reuse rate K is 7/21 is shown schematically.</figref><figref num="3">It is a figure which shows the relationship of the CINR of the downlink in the cellular communication system which uses the frequency reuse rate 1.</figref><figref num="4">In a general cellular communication system, the relationship of CINR according to the separation distance from the base station when the frequency reuse rate is 1 (K = 1) and when the frequency reuse rate exceeds 1 (K&gt; 1) It is a graph which shows.</figref><figref num="5">It is a figure which shows schematic the frequency resource allocation operation based on the multiple frequency reuse rate in the OFDMA cellular communication system by embodiment of this invention.</figref><figref num="6">It is a figure which shows the procedure which generates the subchannel based on the multiple frequency reuse rate in the OFDMA cellular communication system by embodiment of this invention.</figref><figref num="7A">It is a figure which shows the procedure which generates the subchannel in the case of applying the frequency reuse rate 1 in the OFDMA cellular communication system by embodiment of this invention.</figref><figref num="7B">FIG. 5 is a diagram schematically showing a set of subchannels as shown in FIG. 7A assigned to cells constituting an OFDMA cellular communication system according to an embodiment of the present invention.</figref><figref num="8A">It is a figure which shows the procedure which generates the subchannel in the case of applying the frequency reuse rate K in the OFDMA cellular communication system by embodiment of this invention.</figref><figref num="8B">FIG. 5 is a diagram schematically showing a group of subchannels as shown in FIG. 8A assigned to sectors constituting cells of an OFDMA cellular communication system according to an embodiment of the present invention.</figref><figref num="9">It is a figure which shows schematic the frequency resource allocation operation based on the multiple frequency reuse rate in the OFDMA cellular communication system by 1st Embodiment of this invention.</figref><figref num="10">It is a figure which shows schematic the frequency resource allocation operation based on the multiple frequency reuse rate in the OFDMA cellular communication system by 2nd Embodiment of this invention.</figref><figref num="11">It is a flowchart which shows the procedure of allocating the frequency resource based on the frequency reuse rate according to the channel state of the terminal in the OFDMA cellular communication system by 2nd Embodiment of this invention.</figref>

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the following description, for the purpose of clarifying only the gist of the present invention, specific description of related known functions or configurations will be omitted.

FIG. 5 shows a cellular communication system (hereinafter referred to as'OFDMA cellular communication system') using the Orthogonal Frequency Division Multiple Access (hereinafter referred to as'OFDMA') method according to the embodiment of the present invention. , Is a diagram schematically showing a frequency resource allocation operation based on a multiple frequency reuse factor.

As shown in FIG. 5, when the terminal (SS) is located in the cell center region 501 adjacent to the base station (BS), the Carrier to Interference and Noise Ratio; ,'CINR') is relatively high, so the frequency reuse rate (K) for the terminal is 1. On the contrary, if the terminal is located in the cell boundary region 503 separated from the base station, the frequency reuse rate for the terminal is greater than 1 (K&gt; 1), thereby the CINR. Prevent the decrease. Of course, when the terminal moves from the cell boundary region 503 to the cell center region 501, allocate a frequency resource that is large, i.e., has a frequency reuse rate of 1 and is small, i.e., has a frequency reuse rate greater than 1. become.

On the other hand, in the OFDMA cellular communication system, frequency resource allocation is performed in units of subchannels, and the subchannels include at least one or more subcarriers. Here, with reference to FIG. 6, a method of generating a subchannel based on a multiple frequency reuse rate will be described in the OFDMA cellular communication system according to the embodiment of the present invention.

FIG. 6 is a diagram schematically showing a procedure for generating a subchannel based on a multiple frequency reuse rate in an OFDMA cellular communication system according to an embodiment of the present invention. Referring to FIG. 6, when the OFDMA cellular communication system uses N subcarriers, the N subcarriers are classified into G groups. Here, each of the above G groups is composed of S subcarriers, and therefore has an N = SxG relationship.

An arbitrary one subcarrier is selected from each of the above G groups to generate a first subchannel. Then, the second subchannel is generated by selecting an arbitrary one subcarrier from each of the G groups excluding the subcarrier assigned to the first subchannel. When the above procedure is repeated until all the subcarriers existing in the above G groups are assigned to the subchannels, the result is a set of subchannels composed of S subchannels. can do.

When the subcarrier selection method for selecting the subcarriers that generate the subchannels is set differently from each other, a new set composed of a total of S subchannels having different subcarriers can also be generated. .. The total number of subchannel sets composed of S new subchannels generated from the above mutually different subcarriers is (S!).^GIt is an individual. Here, the combination of subcarriers constituting the subchannel is referred to as "subcarrier combination".

Hereinafter, for convenience of explanation, the total (S!) Consisting of the above S subchannels^GA set of any nth subchannel out of a set of subchannels_nDefined as the above set of subchannels A_nAny mth subchannel that makes up

<maths num="1"><img file="JP2010141940A_D0001.tif" /></maths>

Is defined as. Where n = [0, (S!)^G], And has a relationship of m = [0, S-1]. Set of the above subchannels A_nS subchannels that make up

<maths num="2"><img file="JP2010141940A_D0002.tif" /></maths>

Each of them is orthogonal to each other. Therefore, the subcarriers constituting each of the S subchannels do not collide with each other.

Also, each of the subchannels that make up each of the different sets of subchannels.

<maths num="3"><img file="JP2010141940A_D0003.tif" /></maths>

Are not orthogonal to each other, that is, the subcarriers constituting each of the above subchannels collide with each other. Also, configure S subchannels (S!)^GOf the set, a set of C subchannels A_nSelect. At this time, the set A of the above C subchannels selected_nWhen any subchannel is selected one by one from, the number of subcarriers having collision characteristics can be uniform. Therefore, the total number of subcarriers having collision characteristics between the sets of two subchannels is proportional to the number of selected subchannels. As a result, the total (S!) Constituting S subchannels^GThe subcarrier is selected from the set of subchannels to generate a set of subchannels. There can be various methods for generating a set of C subchannels in which the combinations of subcarriers are different from each other and the collision characteristics are uniform.

Hereinafter, in the above-mentioned OFDMA cellular communication system, a method of operating a subchannel having a frequency reuse rate of 1 will be described. First, if a frequency reuse rate of 1 is applied, then all subcarriers in any one cell of the OFDMA cellular communication system, i.e., all subchannels, can be used in adjacent cells.

Here, when using a set of subchannels in which each of the cells has the same combination of subcarriers, that is, a set of subchannels in which each of the cells is the same A_nWhen using, each of the subchannels of the set of subchannels encounters a channel situation in which the interfering component is present or absent. Thus, such channel status, channel the currently measured if Le information is applied to the time interval for the next, it is impossible to predict the channel characteristic.

Hereinafter, a method of generating a subchannel when the frequency reuse rate 1 is applied will be described with reference to FIGS. 7A and 7B. FIG. 7A is a diagram schematically showing a procedure for generating a subchannel when a frequency reuse rate of 1 is applied in an OFDMA cellular communication system according to an embodiment of the present invention. Referring to FIG. 7A, first, when the OFDMA cellular communication system uses N subcarriers, a set of C subchannels from the N subcarriers is applied by applying different subcarrier selection methods. A_nCan be generated. FIG. 7B is a diagram schematically showing an operation of allocating a set of subcarriers corresponding to FIG. 7A to cells constituting the OFDMA cellular communication system.

Seeing Figure 7B, a set of C subchannels A_nIs assigned to each of the cells constituting the OFDMA cellular communication system. Here, the set A of the above C subchannels_nEach of the subchannels constituting the above has orthogonality with other subchannels in the same set of subchannels, and has uniform collision characteristics with the subchannels constituting a set of different subchannels. Therefore, a set of C subchannels A_nIs assigned to each cell, the interference components from adjacent cells are averaged by the uniform collision characteristics of the subcarrier. That is, if the amount of resources used in the adjacent cell is not changed, the validity of the channel state information measured for each preset time unit can be maintained. In such a method, the OFDMA cellular communication system can efficiently operate the subchannel based on the frequency reuse rate 1.

However, in this case, even if the amount of interfering components between adjacent cells can be averaged, CINR itself can be reduced due to the interfering components from all adjacent cells. In particular, the CINR is significantly reduced in the cell boundary region.

On the other hand, a modulation scheme having a very low error correction coding rate and a very low modulation order can be applied to terminals located in the cell boundary region in order to secure the service area of the wireless cellular communication system. However, modulation schemes with very low error correction coding rates and very low modulation orders reduce bandwidth efficiency, thereby providing very high transmission rates assisted by terminals located in the cell boundary region. Decrease.

Next, with reference to Table 1, in the OFDMA cellular communication system based on the frequency reuse rate 1, the average transmission rate of terminals by cell radius and the average transmission rate by cell radius will be described. The values shown in Table 1 are when the channel environment uses a round robin scheduling method that takes into account all long-term fading and short-term fading. It is a value obtained through a simulation test. That is, after the cells / sectors have a predetermined area and are divided into a plurality of concentric circles that do not overlap each other, the average transmission rate of each terminal assigned to each concentric circle is obtained. Then, for the average transmission rate of each of the above terminals, the average transmission rate for each radius (by concentric circles) is obtained. In Table 1, the cell radii are normalized to the maximum cell radius.

Therefore, the average transmission rate for each radius can be defined by a function of the transmission rate of each terminal with respect to the area of the cell area. The average transmission rate of the terminals shown in Table 1 is the average value of the transmission rate of each terminal assigned to each concentric circle, and the average transmission rate of the terminals decreases toward the boundary region of the cell or sector. For this reason, the average transmission rate when the area of the concentric circles is the largest is lower than the average transmission rate near the central region of the cell / sector. This is a result of the interfering components of the adjacent cells / sectors of the OFDMA cellular communication system using a frequency reuse rate of 1.

<tables num="1"><img file="JP2010141940A_D0004.tif" /></tables>

As described above, the OFDMA cellular communication system uses the frequency reuse rate K in consideration of the interference component from the adjacent cell / sector. That is, it limits the use of frequency resources that can interfere with each other in adjacent cells / sectors. For example, an OFDMA cellular communication system with a frequency reuse rate of K uses K different frequency bands, or logically divides the subcarriers contained in one band into K subcarrier groups. To do.

In particular, in the embodiment of the present invention, the subcarriers included in one frequency band are divided into K subcarrier groups, and the frequency reuse rate K is operated based on the K subcarrier groups.

Hereinafter, with reference to FIGS. 8A and 8B, a procedure for generating a subchannel when the frequency reuse rate K is applied in the OFDMA cellular communication system according to the embodiment of the present invention will be described.

FIG. 8A is a diagram schematically showing a procedure for generating subchannels when the frequency reuse rate K is applied in the OFDMA cellular communication system according to the embodiment of the present invention. With reference to FIG. 8A, the subcarriers constituting one frequency band are divided into K subcarrier groups, and the frequency reuse rate K is operated based on the K subcarrier groups. In FIG. 8A, the frequency reuse rate K is 3 (K = 3).

First, the S subchannels that make up the set An of arbitrary subchannels are classified into three mutually exclusive subchannel groups. Here, each of the above three subchannel groups

<maths num="4"><img file="JP2010141940A_D0005.tif" /></maths>

Is defined as. FIG. 8B schematically shows how to allocate subchannel groups as shown in FIG. 8A to the sectors that make up the cells of an OFDMA cellular communication system.

Referring to FIG. 8B, with the frequency reuse rate 3 applied, the above three subchannel groups

<maths num="5"><img file="JP2010141940A_D0006.tif" /></maths>

Is assigned to each of the sectors in the above cell. In the ideal case, there is almost no cell / sector interference component, which increases the average transmission rate of SS located in the boundary region of the cell or sector. However, the amount of resources allocated to each cell or sector is reduced by a third, resulting in a reduction in the overall capacity of the cell or sector.

Hereinafter, in the OFDM communication system based on the frequency reuse rate 1 and the frequency reuse rate 3, the average transmission rate of the sector with respect to the cell radius will be described with reference to Table 2. The values shown in Table 2 are simulation tests when the channel environment uses a round robin scheduling method that takes into account all long-term and short-term fading. It is a value obtained through. It is a value considering all cases where the round robin scheduling method is used and the channel environment is long-term and short-term fading. In Table 2, the cell radii are normalized to the maximum cell radius.

<tables num="2"><img file="JP2010141940A_D0007.tif" /></tables>

As can be seen from Table 2, the OFDMA cellular communication system using the frequency reuse rate 3 has an excellent transmission rate in the boundary region of the cell or sector as compared with the OFDMA cellular communication system using the frequency reuse rate 1. On the other hand, in the cell center region adjacent to the base station, a degraded transmission rate is provided. This is because in the cell center region adjacent to the base station, long-term fading reduces the effect of interference from adjacent cells or sectors. Also, since an OFDMA cellular communication system that uses a frequency reuse rate of 3 can use 1/3 of the frequency resources, the system capacity is also reduced.

Hereinafter, a method of simultaneously using the frequency reuse rates 1 and K in order to improve the bandwidth efficiency of the OFDM communication system and the capacity of the system according to the embodiment of the present invention will be described. As explained with reference to FIG. 5, terminals located in the cell center region adjacent to the base station are relatively less affected by interference from adjacent cells / sectors, and therefore operate based on the frequency reuse rate of 1. And terminals located in the cell boundary region can operate at a frequency reuse rate of K (K&gt; 1) to reduce the effects of interference from adjacent cells / sectors. That is, by using the frequency reuse rates 1 and K at the same time in the above-mentioned OFDMA cellular communication system, the interference effect in the cell / sector boundary region of the frequency reuse rate 1 and the cell / sector boundary region of the frequency reuse rate K The phenomenon of capacity reduction can be overcome at the same time.

On the other hand, if the above-mentioned OFDMA cellular communication system uses the frequency reuse rate 1 and the frequency reuse rate K without physical distinction, the frequency reuse of the adjacent cell / sector is applied to the terminal to which the frequency reuse rate K is applied. The interference component from the terminal to which the rate 1 is applied becomes very large, the CINR decreases, and the performance deteriorates sharply. Therefore, in order to solve the problems that occur when applying multiple frequency reuse rates, that is, multiple frequency reuse rates, ensure orthogonality between the frequency resources to which each frequency reuse rate is applied. There must be. That is, the use of each frequency reuse rate is separated from the time domain or frequency domain in consideration of the time resources and frequency resources that are usable resources of the OFDMA cellular communication system.

Hereinafter, a method of allocating frequency resources based on the multiple frequency reuse rate according to the first embodiment and the second embodiment of the present invention will be described. According to the first embodiment of the present invention, frequency resources are allocated by providing orthogonality between frequency reuse rates in the time domain, and according to the second embodiment of the present invention, between frequency reuse rates in the frequency domain. Provides orthogonality.

First, with reference to FIG. 9, a method of allocating frequency resources based on the multiple frequency reuse rate will be described in the OFDMA cellular communication system according to the first embodiment of the present invention. FIG. 9 is a diagram schematically showing a frequency resource allocation operation based on the multiple frequency reuse rate in the OFDMA cellular communication system according to the first embodiment of the present invention.

As shown in FIG. 9, according to the frequency resource allocation method of the present invention, a predetermined time domain, for example, one frame 900, is a time domain with a field 903 using a frequency reuse rate of 1 and a frequency reuse. Divided into fields 905 that use utilization K. All cells / sectors of the OFDMA cellular communication system are sub-differentiate from each other so that in field 903, which has a frequency reuse rate of 1, all cells / sectors can operate at a frequency reuse rate of 1. Use a set of channels. In field 905, where the frequency reuse rate is K, each cell / sector uses the same set of subchannels so that each cell / sector can operate at the frequency reuse rate K. In particular, a set of subchannels can be generated from K exclusive groups and only one of them can be used.

Hereinafter, with reference to FIG. 10, a procedure for allocating frequency resources based on the multiple frequency reuse rate will be described in the OFDMA cellular communication system according to the second embodiment of the present invention. FIG. 10 is a diagram schematically showing a procedure for allocating frequency resources based on the multiple frequency reuse rate in the OFDMA cellular communication system according to the second embodiment of the present invention.

Referring to FIG. 10, when the OFDMA cellular communication system uses N subcarriers, the N subcarriers are divided into G groups. Here, each of the above G groups is composed of S subcarriers, and therefore has an N = SxG relationship. Further, each of the above G groups is divided into two subgroups, and each of the above two subgroups is S.₁Subcarriers and S_KIncludes subcarriers.

First, an arbitrary one subcarrier is selected from each of the above G subgroups to generate a first subchannel. Then, an arbitrary one subcarrier is selected from each of the G subgroups excluding the subcarrier assigned to the first subchannel to generate the second subchannel. The subchannel generation operation as described above is repeated until all the subcarriers existing in the G subgroups are assigned to the subchannels. As a result, total S₁It is possible to generate a set of subchannels composed of a number of subchannels. Further, as described above, a new set A of C subchannels having a subcarrier different from the subcarrier is different from each other in the method of selecting the subchannel._nCan also be generated. Therefore, the above new set A_nEach of the sub-channels constituting the above has orthogonality with other sub-channels in the same set of sub-channels while exhibiting uniform collision characteristics with respect to the sub-channels of the set of other sub-channels. Set of the above subchannels A_nCan be operated with a frequency reuse rate of 1 by assigning to each cell / sector.

Then, the above S_KA first subchannel is generated by selecting any one subcarrier from each of the G subgroups containing the subcarriers. Then, an arbitrary one subcarrier is selected from each of the G subgroups excluding the subcarrier assigned to the first subchannel to generate the second subchannel. The subchannel generation operation as described above is repeated until all the subcarriers constituting the G subgroups are assigned to the subchannels. As a result, total S_KIt is possible to generate a set of subchannels composed of a number of subchannels. After the subchannel is divided into K exclusive subchannel groups, it is assigned to each of the K cells / sectors, so that the cells / sectors operate at the frequency reuse rate K. be able to. In particular, since the subchannel using the frequency reuse rate 1 and the subchannel using the frequency reuse rate K include subcarriers different from each other, the frequency reuse rate 1 and the frequency reuse rate K are operated at the same time. Even in this case, mutual interference can be prevented.

Table 3 shows the simulation test results of the OFDMA cellular communication system that carries out the frequency resource allocation method based on the multiple frequency reuse rate according to the first embodiment and the second embodiment of the present invention.

In the above simulation test, the ideal antenna model and the actual antenna model are applied to each sector, and the average unit transmission rate for the sector of the central cell is applied to the sectors and cells, so that 3 sectors and 19 sectors are applied. Performed on the cell. In addition, the above simulation test results are obtained under the condition of a path decay index of 3.8. The simulation test is performed with a single path model, taking into account fading, applying a shadowing standard deviation of 8 dB when shadowing is shown.

When the frequency reuse rate 3 is applied, time resources and frequency resources are supported so that interference between the three sectors is minimized. Further, the frequency reuse rate 1 and the frequency reuse rate 3 are assigned to the OFDMA cellular communication system at the same ratio. That is, in the time domain, the length of the section having the frequency reuse rate of 1 and the length of the section having the frequency reuse rate of 3 are made the same, and in the frequency domain, S₁= S_KThe above simulation test was carried out by setting so as to have the relationship of.

<tables num="3"><img file="JP2010141940A_D0008.tif" /></tables>

As shown in Table 3, when the frequency reuse rate 1 and the frequency reuse rate 3 are applied to the OFDMA cellular communication system according to the first embodiment and the second embodiment of the present invention, only the frequency reuse rate 1 is applied. Compared to the system performance of the OFDMA cellular communication system to which is applied, the system performance can be improved by about 10% or more from the viewpoint of the average unit transmission rate (Bits / Hz / Sec) per sector.

As mentioned above, frequency resources with different reuse rates are allocated when transmitting the actual user packet. That is, a frequency resource (OFDM symbol or subchannel) with a predetermined frequency reuse rate is allocated for transmission of user packets based on the channel state of the receiver. Here, the channel state of the receiver includes the amount of interference at the receiver or the measured value corresponding to the interference. In the present invention, the above CINR is taken as an example. In particular, when the frequency reuse rate is 1, the amount of interference with the frequency resource is the largest, so that the frequency resource can be allocated using the CINR for this. The frequency resource allocation according to the channel state of the receiver is performed so that the user packet transmitted to the receiver having the CINR with the highest frequency resource having a frequency reuse rate of 1 is allocated. The frequency resource with the highest frequency reuse rate is ultimately allocated to the user packet sent to the receiver with the lowest CINR.

FIG. 11 is a flowchart showing a procedure for allocating frequency resources classified by frequency reuse rate according to the channel state of the terminal in the OFDMA cellular communication system according to the second embodiment of the present invention.

Referring to FIG. 11, channel state information is fed back from each terminal to the base station (step S1101), and the base station allocates frequency resources having different frequency reuse rates according to the channel state information of the terminal (step S1101). Step S1102). Then, in step S1102, the base station classifies the corresponding terminals according to the frequency resources assigned to the terminals and having different frequency reuse rates for data transmission (step S1103), and the classified terminals. Is scheduled according to a preset scheduling algorithm, and the corresponding data is transmitted (step S1104).

Although the details of the present invention have been described above based on specific embodiments, it is clear that various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention is not limited to the above-described embodiment, and should be defined by the description of the scope of claims and the equivalent of the description.

501 cell center area 503 cell boundary area 900 1 time domain frame 903 Fields that use frequency reuse rate 1 905 Fields that use frequency reuse rate K