JP5340226B2 - Inter-cell interference avoidance communication method and communication system - Google Patents

Description

  The present invention relates to an inter-cell interference avoidance communication method in a communication system including a plurality of mobile terminals and a plurality of base stations connected to the mobile terminals.

3GPP LTE which normalized by (3 ^rd Generation Partnership Project) has been promoted (Long Term Evolution) or, IEEE (Institute of Electrical and Electronics Engineers) next-generation mobile communication system such as WiMAX which standardization is in progress in , OFDM (Orthogonal Frequency Division Multiplexing) is adopted as a wireless communication system. OFDM is a communication method that uses a plurality of orthogonal carriers (subcarriers) and multiplexes and transmits a plurality of user data on the frequency axis and the time axis.

  Recently, partial frequency repetition (FFR), which is a frequency repetition method that occupies between 1-cell repetition and conventional N-cell repetition, has been studied by utilizing the flexible subcarrier allocation characteristics of OFDM. Yes.

  In FFR, subcarriers used in the vicinity of the cell edge are limited, and interference between cells is avoided by not using the same subcarrier between adjacent cells. In an actual communication system, a plurality of subcarriers (frequency) and symbols (time) are collectively allocated to a mobile device as one allocation unit (subchannel). In FFR, a set of subchannels is divided so as not to overlap between adjacent cells, and a divided subset is used at the cell edge. However, a band that can be used at the cell edge regardless of any division method. Will be fixed. Therefore, when the mobile station moves and the ratio of the cell edge mobile device to the non-cell edge mobile device in the same cell or the ratio of the cell edge mobile device between cells fluctuates, the frequency utilization efficiency increases. There was a problem of lowering.

  As a method for solving the above problem, Patent Document 1 discloses a technique related to an adaptive FFR scheme that dynamically changes a subchannel set used at a cell edge. Adaptive FFR is based on a set of subchannels defined by conventional FFR (hereinafter referred to as static FFR), and a certain subchannel is to be used at the cell edge of another cell according to traffic at the cell edge. Accordingly, the frequency use efficiency is increased and the probability of occurrence of inter-cell interference is kept low.

  Also, a technique for assigning radio resources in consideration of inter-cell interference is disclosed in Patent Document 2 below. This technology formulates mobile unit scheduling and inter-cell interference avoidance as optimization problems such as optimal resource allocation problems, graph coloring problems, and linear programming, and handles them in a unified manner. Since the amount of interference between mobile stations is measured and frequency repetition at the subcarrier level is performed, efficiency is improved from the viewpoint of frequency reuse.

JP 2009-510967 A International Publication No. 2009/019079

  However, according to the conventional technique (Patent Document 1), since the static FFR is used as a base, information on the subchannels used at the cell edge of the own cell and at the cell edge of the own cell is acquired in advance. Is assumed. Therefore, there has been a problem that it cannot cope with a system in which a base station moves or power is turned on / off like a femtocell, and cell adjacency constantly changes.

  Further, according to the conventional technique (Patent Document 2), since interference avoidance and radio resource allocation are integrated, there is a problem that the base station cannot be freely scheduled. For example, the subchannel to be used by each mobile station is determined by the inter-cell interference avoidance process. In order to achieve radio resource allocation that follows fluctuations in short-term radio communication quality while avoiding interference, it is necessary to allocate radio resources in consideration of interference avoidance at least every scheduling period. However, it is difficult to implement radio resource allocation for all mobile devices distributed in a plurality of cells in the order of several ms while considering inter-cell interference.

  The present invention has been made in view of the above, and provides an inter-cell interference avoidance communication method capable of dynamically changing a subchannel set used at each cell edge in response to fluctuations in traffic at the cell edge. The purpose is to obtain.

  In order to solve the above-described problems and achieve the object, the present invention provides a communication composed of a plurality of mobile devices, a plurality of base stations connectable to the mobile devices, and a server connected to the plurality of base stations. An inter-cell interference avoidance communication method in a system, in which each mobile device measures and measures the communication quality of a signal in an adjacent cell that is adjacent to a cell of a predetermined base station to which the mobile device is connected. A measurement step of notifying the predetermined base station of the communication quality and the identification number of the adjacent cell, and the predetermined base station positioning the mobile device that has notified the communication quality equal to or higher than the predetermined communication quality at the cell edge of the own cell A determination step of determining that the neighboring cell is an interference avoidance target cell based on the identification number of the neighboring cell received together with the communication quality, and the predetermined base station Located on the edge A required bandwidth setting step of setting a required bandwidth of a subchannel to be allocated to a mobile station, and notifying the server of the required bandwidth and an identification number of the interference avoidance target cell; and the server includes the predetermined base Based on the identification number of the interference avoidance target cell received from each base station that is a station and the required band, an interference graph is generated to solve the multiple coloring problem, and the frequency band of the cell is equally divided by the number of colors. A first allocation step of associating a subchannel with each color so that the subchannel band becomes equal for each mobile station at the end, and allocating subchannels corresponding to the number of mobile stations at the cell end to each base station; As a result of the server solving the multi-coloring problem, a mobile station at a cell edge of a base station in which a subchannel allocated to a specific base station constitutes another cell Or a second allocation that allocates, as a surplus subchannel, a subchannel allocated to the specific base station to a base station that configures the other cell when it can be used by a mobile device at a non-cell edge A first notification step of notifying each of the base stations of the subchannel allocated by the server in the first allocation step, and a surplus subchannel in the second allocation step. Is assigned, the second notification step of notifying the surplus subchannel to the base station constituting the another cell, and the base station notified of the subchannel in the first notification step, A first scheduling step for assigning subchannels to mobile stations located at a cell edge of the own station, and a surplus subchannel in the second notification step. The notified base station further includes a second scheduling step of allocating the surplus subchannel to a cell-edge mobile device or a non-cell-edge mobile device.

  According to the present invention, there is an effect that the subchannel set used at each cell edge can be dynamically changed in response to fluctuations in traffic at the cell edge.

FIG. 1 is a diagram illustrating cell arrangement and mobile device distribution. FIG. 2 is a diagram illustrating bandwidth allocation of subchannels. FIG. 3 is a diagram illustrating bandwidth allocation of subchannels. FIG. 4 is a diagram illustrating a configuration example of a network. FIG. 5 is a flowchart showing a process for determining a subchannel set. FIG. 6 is a diagram showing a set of vertices. FIG. 7 is a diagram showing an enlarged graph. FIG. 8 is a diagram illustrating an example of subchannel allocation. FIG. 9 is a diagram showing the sum of the data rates and the required bandwidth of the cell edge mobile device. FIG. 10 is a flowchart showing a reservation process for a spare subchannel set.

  Embodiments of an inter-cell interference avoidance communication method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating cell arrangement and mobile station distribution for explaining a conventional static FFR scheme. Cells 1 to 7 are omnicells having the same cell radius. In order to arrange the cells efficiently and universally, each cell is assumed to be arranged in a honeycomb shape as a virtual hexagon as shown in the figure. Each cell is formed by the base stations 11 to 17. For example, the fact that the base station 12 forms the cell 2 is expressed as “2 @ 12”. The mobile devices 21 to 23 are located at the cell edge of the cell 1 and are connected to the base station 11 to perform wireless communication. Similarly, the mobile device 24 is located at the cell 2 and the mobile devices 25 and 26 are located at the cell ends of the cell 7 and are connected to the base station 12 and the base station 17 for wireless communication.

  Assuming the cell arrangement of FIG. 1, in the conventional static FFR, three different subchannel sets are repeatedly allocated to each base station so as to be different subchannel sets between adjacent cells. In FIG. 1, a subchannel set is represented by a cell pattern, where cell 1 is one subchannel set, cells 2, 4, and 6 are other subchannel sets, and cells 3, 5, and 7 are further different subchannel sets. Is used.

  As shown in FIG. 2, 1/3 of the total bandwidth is assigned to each subchannel set. FIG. 2 is a diagram illustrating bandwidth allocation of each subchannel. FIG. 2 (a) shows a method of using a subchannel set in the cell 1, and the mobile station located at the cell edge has, for example, the lowest frequency 1 / of all frequency bands usable in the cell. 3 is used, and the remaining 2/3 is used by the mobile station located at the non-cell edge. Here, in FIG. 2A, the transmission power of the subchannel set used by the mobile station located at the non-cell edge is smaller than that at the cell edge. This is because at the non-cell edge, there is a possibility that the same frequency is used between adjacent cells at the same time.

  Similarly, FIG. 2 (b) shows a method of using the subchannel set in the cells 2, 4, and 6, and the mobile station located at the cell edge is shown in FIG. A mobile unit that uses a portion other than the set of subchannels used at the cell edge shown in 2 (a), for example, a central 1/3 area and the remaining 2/3 area at the non-cell edge. use. FIG. 2 (c) shows how to use the subchannel set in the cells 3, 5, and 7. The 1/3 region having the highest frequency is used as the used subchannel set at the cell edge, and the rest. Use 2/3 on the mobile station located at the non-cell edge.

  In the conventional static FFR, since the subchannel set used at the cell edge is fixed, if the distribution of mobile devices located at the cell edge is biased, the utilization efficiency of the radio band is lowered. For example, in the distribution of the mobile devices 21 to 26 shown in FIG. 1, as shown in FIG. 2, in the cell 1, three mobile devices 21 to 23 use 1/3 of the entire band (1/9 per mobile device). Cell 2 uses one mobile device 24 (uses 1/3 bandwidth per mobile device), and cell 7 uses two mobile devices 25 and 26 (1/6 mobile device). (Use bandwidth) each uses 1/3 bandwidth, and there is a difference in available bandwidth per mobile device. In addition, in cells such as cells 3 to 6 where no mobile station is located at the cell edge, subchannel sets for cell edge mobile stations assigned to each cell can be used in adjacent cells. It becomes unused.

  Therefore, in the inter-cell interference avoidance communication method of the present embodiment, in FFR, considering the number of mobile stations located at the cell edge, the amount of traffic generated at the cell edge, the relationship between the distribution of mobile stations and interference, etc. A subchannel set to be used at the cell edge is determined.

  For example, in FIG. 1, the downlink transmission of cell 1 (or cell 2) becomes interference with mobile station 24 (or mobile station 23) located at the cell edge of cell 2 (or cell 1), and downlink transmission of cell 7 Interference with the mobile unit 23 located at the cell edge of the cell 1 occurs. Therefore, a subchannel set to be used at the cell edge is defined by dividing the equal radio band between the cell 1 and the cell 2 and the cell 1 and the cell 7 in the interference relationship, and as shown in FIG. 2 and cell 7 divide the frequency band so that a subchannel set equivalent to 1/5 of the entire band can be used per mobile station. FIG. 3 is a diagram illustrating bandwidth allocation of each subchannel. FIG. 3A shows subchannel set allocation in the cell 1, and the subchannel sets 40 corresponding to 3/5 of the entire band are used by the three mobile devices 21 to 23. Similarly, FIG. 3B shows allocation of subchannel sets in the cell 2, and a subchannel set 41 corresponding to 1/5 of the entire band is used by one mobile device 24. FIG. 3C shows assignment of subchannel sets in the cell 7, and the subchannel sets 42 corresponding to 2/5 of the entire band are used by the two mobile devices 25 and 26.

  Further, in the FFR of the present embodiment, it is possible to define a surplus subchannel set that can be used by both a cell edge mobile device and a non-cell edge mobile device. For example, in FIG. 3B, since only the mobile device 24 is located at the cell edge in the cell 2, it is sufficient that the subchannel set 41 corresponding to 1/5 of the entire band can be used. However, in the cell 2, even if the subchannel set 43 is used at the cell edge, it does not interfere with adjacent cells, so that it can be used in the mobile device 24. Here, the subchannel set 43 is set as a surplus subchannel, and the base station 12 can be assigned to a cell edge or non-cell edge mobile station according to its own scheduling algorithm.

  Next, a method for adaptively determining a subchannel set to be used at the cell edge according to the distribution of the cell edge mobile station in downlink communication from the base station to the mobile station will be described in detail. In addition, it is applicable also to the uplink communication from a mobile station to a base station direction, and frequency division multiplexing (FDD) and time division duplex (TDD) using different frequencies for uplink and downlink are used. ).

  FIG. 4 is a diagram illustrating a configuration example of a network capable of realizing the inter-cell interference avoidance communication method according to the present embodiment. The network includes base stations 11 to 17, mobile devices 21 to 26, and an ICE (Interference Coordination Entity) 50. The arrangement of the base stations 11 to 17 and the mobile devices 21 to 26 is the same as that in FIG. The ICE 50 is connected to the base stations 11 to 17 constituting each cell, and the subchannel used at each cell end based on the interference relationship between the cells notified from each base station and the required bandwidth information at each cell end. A server (network entity) that determines a set. The ICE 50 may be mounted as a special device or may be mounted in an existing device.

  FIG. 5 is a flowchart showing processing for determining a subchannel set to be used at the cell edge in the FFR of the present embodiment.

  First, the ICE 50 waits until the update period of the previously determined subchannel set elapses in order to update the subchannel set used at the cell edge at regular intervals (step S1).

  Next, the mobile devices 21 to 26 monitor the monitor channels of the neighboring cells, and the received cell and the reception quality and the cell identification information of the monitor channels of the cells are the base stations constituting the cell to which the mobile devices 21 to 26 are connected. To notify.

  Each base station determines whether or not the mobile device is located at the cell edge based on the reception quality of the monitor channel of the neighboring cell notified from the mobile device. When it is determined that the mobile station is located at the cell edge, each base station uses the neighboring cell adjacent to the mobile station as an interference avoidance target cell, and each base station requests assignment to the cell edge mobile station in the cell. Find the required bandwidth of the set. Each base station determines that it is located at the cell edge when the reception quality notified from the mobile device is a certain level or higher.

  Here, the monitor channel is a broadcast channel broadcast in each cell or another downlink common channel. The cell identification information is information that uniquely identifies each cell at least between adjacent cells, and a physical / logical cell identifier, a scramble code number, or the like can be used. The required bandwidth of the subchannel set is for determining the division ratio of the subchannel set when dividing the subchannel set in order to avoid interference with adjacent cells. Here, for simplification of description, the number of mobile stations located at the cell edge is used. Note that the required bandwidth of the subchannel set need not be limited to this. For example, the data transmission / reception rate in the mobile station located at the cell edge, the buffer in the mobile station (in the case of uplink) or the base station (in the case of downlink) A total value, logarithmic value, or average value of the data amount for the cell edge mobile device staying in the cell may be used.

  Each base station notifies the ICE 50 of information on the interference avoidance target cell and the required band. Then, the ICE 50 collects information on the interference avoidance target cell and the required band from each base station (step S2).

  The ICE 50 collects the latest interference avoidance target cell and required band information from each base station after the subchannel set allocation period elapses, but is not limited thereto. For example, the ICE 50 collects information on the interference avoidance target cell and the required band from each base station periodically or at an arbitrary timing, and assigns the subchannel set using the latest information when the subchannel set assignment period elapses. It may be updated.

  Next, the ICE 50 generates an interference graph using the information collected from each base station (step S3). First, in the ICE 50, based on the interference avoidance target cell collected from each base station and the required band (the number of cell edge mobile devices), a weighted undirected graph “G = (V, E)” based on the following rules: “W: V → I” is generated. Here, V is a set of vertices of G, E is a set of sides of G, and I is a set of non-negative integers.

1. For each cell i, “iεV”, “w (i) = N _i ”. Here, N _i is the number of mobile units located at the cell edge of cell i.

  2. For each cell i, for each interference avoidance target cell j reported from the corresponding base station, if “w (i) · w (j)> 0”, “{i, j} εE”.

3. G is divided as an independent subgraph as shown in the following equation (1).

4). Let G _i satisfying | V _i |> 1 be an interference graph. Here, | S | represents the number of elements of the set S.

  When the graph G is generated with respect to the distribution of mobile devices shown in FIG. 1, the result is as shown in FIG. FIG. 6 is a diagram showing a set of vertices. In FIG. 6, each vertex corresponds to the cell in FIG. 1, and the cell number corresponding to the vertex name is given. Further, the required bandwidth at the cell edge of each cell is shown in the apex horizontal square. For example, the vertex 71 corresponds to the cell 3, and since there is no mobile device at the cell end in the cell, 0 is written in the required bandwidth 75. Also, the side connecting the two vertices indicates that adjacent cells are in an interference relationship, and it is necessary to use different subchannel sets at the cell edges between these cells.

  When the graph G is divided into subgraphs that are not connected by edges, a subgraph consisting of only the vertices of the vertices 71 to 74 and the vertices and edges corresponding to the cells 1, 2 and 7, respectively. It becomes. In the subgraph composed of only one vertex of each of the vertices 71 to 74, the number of vertices is 1 or less, that is, there is no interference relationship with other cells, and it is not necessary to divide the subchannel set used at the cell edge. Therefore, the interference graph is not used, and the corresponding base station is notified of the entire band as a set of subchannels that can be used at the cell edge. On the other hand, for the graph 70, sub-channel set allocation described later as an interference graph is performed.

Next, for each interference graph G ^Int = (V ^Int , E ^Int ) obtained in step S3, the ICE 50 determines assignment of subchannel sets to each cell, specifically, to the base stations constituting each cell. (Step S4). Specifically, the following procedure is used.

1. “W ′ (i) = w (i) / w _min (G ^Int )”, “i∈V ^Int ”. Here, w _min (G ^Int ) is the minimum weight in G ^Int .

2. G w'each vertex "i∈V ^Int" of ^Int (i) number of vertex _{i 0, i 1, ...,} i w '(i) expansion was replaced by a complete graph consisting _-1 graph "G ^{Int, Ext} = (V ^{Int, Ext} , E ^{Int, Ext} ) ”.

3. Coloring is performed on G ^{Int, Ext} , and the coloring number “c: V ^{Int, Ext} → {0, 1,..., M−1}” and the number of colors M are obtained for each vertex “i∈V ^{Int, Ext} ”.

4). Multiple color “c ′: V ^Int → C⊆ {0, 1,..., M−1}” for each vertex “i∈V ^Int ” of G ^Int is expressed as “c ′ (i) = {c (j): j is an expanded node of i in G ^{Int, Ext} } ”.

  5. A subchannel set corresponding to a bandwidth of B / M is assigned to each color {0, 1,..., M−1} (a subchannel set corresponding to each color m is S (m)). Here, B is the frequency bandwidth of the cell.

6). For each vertex “i∈V ^Int ” of G ^Int
(A) A surplus color set “R (i) = φ”.
(A) For all G ^Int maximal cliques including vertex i, U (i) is the set of colors used in the corresponding G ^{Int, Ext} maximal clique. Here, when an edge exists between any two different vertices in a subgraph of a certain graph, the subgraph is defined as a clique. When a vertex set is not truly included in any other clique among cliques, the clique is set as a maximum clique.

7). Thereafter, the process is repeated until there are no vertices to which an extra color can be assigned.
(A) Select an arbitrary vertex “i∈V ^Int ” of G ^Int (a) When “{0, 1,..., M−1} −U (i) ≠ φ”
(1) “mε {0, 1,..., M−1} −U (i)” is arbitrarily selected, and “R (i) = R (i) ∪ {m}” is set.
(2) “U (i) = U (i) Ｇ {m}” is set for each vertex j (including i) of all maximal cliques of G ^Int including vertex i.

8). A set of subchannels that can be used by the cell edge mobile station of the cell corresponding to the vertex “i∈V ^Int ” is represented by “F _edge (i) = {s∈S (m): m∈c ′ (i)}”, A set of surplus subchannels that can be used in all mobile stations is assumed to be “F _all (i) = {sεS (m): mεR (i)}”.

  The normalization of the interference graph weight in the above procedure 1 is provided in order to reduce the number of vertices of the enlarged graph and reduce the calculation amount of the algorithm for solving the coloring problem. . When the number of subchannels occupying the frequency bandwidth B in the procedure 4 is smaller than the number of colors M, the time axis (slot, TTI (Transmission Time Interval), subframe, frame, etc. depending on the target communication system) Also consider the above allocation.

For example, in the interference graph 70 illustrated in FIG. 6, the minimum vertex weight is 1 of vertex 2, and “w ′ (i) = w (i)”. FIG. 7 shows an enlarged graph in which each vertex of the interference graph is replaced with a complete graph composed of w ′ (i) vertices. FIG. 7 is a diagram showing an enlarged graph. In FIG. 7, the vertices 1 ₀ , 1 ₁ , 1 ₂ after the enlargement of the vertex 1 are connected to the enlarged vertices 7 ₀ , 7 _{1 of the} vertex 2 and the vertex 7, respectively. In this enlarged graph, if the vertices connected at the sides are colored so as to have different colors, for example, the vertices can be painted separately as indicated by the numbers in the diamonds in FIG. " In the interference graph, the maximum clique stretched between the vertices 1 and 7 uses five colors, so that “R (1) = R (7) = φ”. However, since the maximal clique stretched between the vertices 2 and 1 uses only four colors, there is a possibility that the subchannel corresponding to the other color can be used at the vertices with the maximal clique, and actually R (2) the vertex ₇₁ is a color that is being used (= 4) in the enlarged graph.

  FIG. 8 shows an example of subchannel allocation to each color when the number of subchannel sets that can be allocated per unit scheduling time by the base station is three. FIG. 8 is a diagram illustrating an example of subchannel allocation. The ICE 50 can assign six subchannel sets to the required number of subchannel sets (= number of colors) 5 by assigning subchannel sets to each color every two scheduling times (= even slots and odd slots). Thus, the subchannel set for one color becomes redundant. In this case, the ICE 50 selects an arbitrary color (color 0 in FIG. 8) and assigns subchannel sets for two colors.

  Then, the ICE 50 defines a subchannel set that can be used at the cell edge of each cell based on the coloring for each vertex of the interference graph determined in step S4, and notifies the base station that configures the corresponding cell (step). S5).

  For example, in FIG. 7, the base station 11 is notified of the subchannel set associated with the vertex 1 by the three colors 0, 1, and 2 as a subchannel set usable at the cell edge of the cell 1. Similarly, a subchannel set associated with cell 2 is notified to base station 12 as a subchannel set usable at the cell edge of cell 2 and a subchannel set associated with color 4 is a surplus subchannel set. To do. After that, each base station assigns a subchannel set to mobile devices in its own cell.

  As described above, in the FFR of the present embodiment, the base station determines neighboring cells that should avoid inter-cell interference based on information from mobile stations distributed at the cell edge of each cell, The required bandwidth at the cell edge of the adjacent cell is set, and the ICE is requested to assign a subchannel set. Based on information collected from each base station, ICE decides subchannel set allocation so as to allocate bandwidth equally to mobile stations located at the cell edge. Thereby, in a communication system, subchannel allocation according to a required band at each cell end can be performed while avoiding inter-cell interference.

  In addition, the assignment of the subchannel set to the base station constituting each cell determined by the ICE 50 places a restriction on the subchannel set used at the cell edge of each cell. Under restrictions, subchannels can be freely assigned to mobile stations. This makes it possible to perform subchannel allocation that follows short-term fluctuations in communication quality. In addition, it is possible to assign a subchannel assigned to an existing mobile device to a cell edge mobile device that has temporarily increased due to handover or outgoing / incoming calls.

  The required bandwidth at each cell edge from each base station to the ICE 50 is set to a value proportional to the number of mobile devices such as the number of mobile devices, the data rate, the amount of data in the mobile device or the buffer in the base station, and the flow rate. A discrete value can be taken for the actual continuous required bandwidth. FIG. 9 is a diagram showing the sum of the data rates and the required bandwidth of the cell edge mobile device. The required bandwidth value for each defined section is shown. As shown in FIG. 9, sections [0, a), [a, b), [b, c), [c, ∞) are defined for the sum of the data rates of the cell edge mobile units in each cell. .Alpha., .Beta., .Gamma., And .delta. [0, a) represents 0 or more and less than a.

Embodiment 2. FIG.
In the first embodiment, the ICE obtains a required band of a subchannel set to be allocated to each base station in order to avoid cell interference based on information on mobile devices distributed at the cell edge of each base station. It was. In this embodiment, when cell edge mobile devices increase due to outgoing / incoming calls, handovers, return from sleep mode, etc., the ICE sends to each base station in advance until the next subchannel set update cycle. A method of applying a reserved small amount of subchannel sets for these new cell edge mobile stations will be described. A different part from Embodiment 1 is demonstrated.

  FIG. 10 is a flowchart showing a reservation process for a spare subchannel set. In step S2 of the flowchart shown in FIG. 5, each base station performs the process shown in FIG. 10 to reserve a small amount of spare subchannel sets.

  First, each base station sets a virtual mobile device for the adjacent cell detected by the cell edge mobile device, and updates the required bandwidth (step S11). In the first embodiment, the base station causes the connected mobile device to monitor the neighboring cell, and the mobile station that has performed the measurement from the measured value of the radio channel quality such as the common channel transmitted by the neighboring cell. It is determined whether the machine is located at the cell edge. When the base station determines that the mobile station is a cell edge mobile device, the base station reports the cell identification information to the ICE 50 with the neighboring cell reported by the mobile device as an adjacent cell for which inter-cell interference should be avoided. At this time, the number of mobile devices determined to be located at the cell edge, the data rate of these mobile devices at the cell edge, and the sum total of the data retention amount in the mobile device / base station buffer are reported to the ICE 50 as a required bandwidth.

  In the present embodiment, assuming a mobile device that can increase due to outgoing / incoming calls, handover, return from sleep mode, etc. by the next subchannel set update cycle, a virtual required bandwidth is added (for example, the required bandwidth is If the number represents the number of mobile units, it is set as one). As a result, in addition to the subchannel set that should be allocated to the mobile station that is currently communicating, it is possible to reserve the subchannel set in advance for the mobile station that has been increased by the next subchannel set update period. It becomes.

  In addition, each base station sets an adjacent cell and a virtual mobile device that are interference avoidance targets based on other adjacent cell information, and calculates a required bandwidth for the adjacent cell (step S12). In Embodiment 1, an adjacent cell that should be a target for avoiding inter-cell interference in each cell is determined by measurement of a mobile station that is communicating at the cell edge of the cell.

  In this embodiment, the neighboring cells that cannot be monitored by the mobile station in communication at these cell edges are defined as neighboring cells that are subject to interference avoidance, and each base station reserves a subchannel set to be allocated to the cell edge mobile station in advance. Therefore, the neighboring cell information corresponding to any of the following is collected, a virtual mobile station and a required band are set for these neighboring cells in the same manner as in step S11, and reported to the ICE 50.

  (1) Monitor cell information reported by a mobile station that has made and received calls in the past at the time of wireless connection setup. Monitor cell information notifies the base station of neighboring cell information measured before establishing a wireless connection when the mobile device establishes a wireless connection for outgoing / incoming calls. Similar to the monitor cell information reported to the base station, it can be used when determining a neighboring cell as an interference avoidance target.

  (2) Neighboring cell information monitored by the mobile station that has been communicating at the cell edge in the past and reported in step S2. In the past, the monitor cell information notified by the mobile station communicating at the cell edge in step S2 is used.

  (3) Handover history. In response to the handover from another cell to the cell, the handover source cell is set as a neighboring cell of the cell.

  (4) Neighbor cell information notified from the ICE 50. The ICE 50 obtains the adjacent relationship between the cells obtained when the interference graph is created from the interference avoidance target cell / required band information collected from each base station in step S3 by feeding back from the ICE 50 to each base station. That is, the adjacent cell is a cell that can be monitored from a mobile station located at the cell edge of the own cell, and a cell that is communicating with a mobile station that can monitor the own cell. Since the latter can be collected only by the ICE 50, the ICE 50 uses the neighbor cell relationship obtained in Step S3 when notifying each base station of the subchannel set in Step S5. Also notify.

  Note that the processes in step S11 and step S12 are independent processes. Therefore, step S12 may be performed first, only step S11 may be performed, or only step S12 may be performed.

  As described above, in the present embodiment, the base station requests an extra required bandwidth in preparation for the case where the number of cell edge mobile devices increases due to outgoing / incoming calls, handover, return from sleep mode, etc. A small amount of subchannel aggregation was secured. As a result, for the cell edge mobile station that has been increased due to outgoing / incoming calls, handover, return from sleep mode, etc. until the next subchannel set update cycle, the base station assigns subchannels from the spare subchannel set. It becomes possible to assign.

  As described above, the inter-cell interference avoidance communication method according to the present invention is useful for a communication method of a communication system including a base station and a mobile device, and is particularly suitable for a communication method of a communication system employing OFDM. Yes.

1 to 7 cells 11 to 17 base stations 21 to 26 mobile devices 50 ICE

Claims (20)

An inter-cell interference avoidance communication method in a communication system including a plurality of mobile devices, a plurality of base stations connectable to the mobile devices, and a server connected to the plurality of base stations,
Each mobile device measures the communication quality of a signal in an adjacent cell that is adjacent to the cell of the predetermined base station to which the mobile device is connected, and the measured communication quality and the identification number of the adjacent cell are A measurement step to notify the base station of
The predetermined base station determines that the mobile device that has notified the communication quality equal to or higher than the predetermined communication quality is located at the cell edge of the own cell, and based on the identification number of the neighboring cell received together with the communication quality A determination step of determining the adjacent cell as an interference avoidance target cell;
The predetermined base station sets the required bandwidth of the subchannel to be allocated to the mobile station located at the cell edge of the own cell, and notifies the server of the required bandwidth and the identification number of the interference avoidance target cell Required bandwidth setting step,
The server generates an interference graph based on the identification number of the interference avoidance target cell received from each base station that is the predetermined base station and the required band, solves the multi-coloring problem, and determines the frequency band of the cell. Equally divide by the number of colors, associate subchannels with each color so that the subchannel bandwidth is equal for each mobile device at the cell edge, and for each base station, subchannels for the number of mobile devices at the cell edge A first assigning step of assigning
As a result of the server solving the multi-coloring problem, a subchannel assigned to a specific base station can be used by a mobile station at a cell edge or a non-cell edge mobile station of a base station constituting another cell. In this case, a second allocation step of allocating a subchannel allocated to the specific base station as a surplus subchannel to a base station configuring the another cell;
A first notification step in which the server notifies the base station of the subchannel allocated in the first allocation step;
A second notification step of notifying the surplus subchannel to a base station constituting the another cell when the server allocates a surplus subchannel in the second allocation step;
A first scheduling step in which the base station notified of the subchannel in the first notification step assigns the subchannel to a mobile device located at the cell edge of the own station;
A second scheduling step in which the base station that has been notified of the surplus subchannel in the second notification step further assigns the surplus subchannel to a cell-edge mobile device or a non-cell-edge mobile device;
An inter-cell interference avoidance communication method comprising: In the required bandwidth setting step, the required bandwidth is set based on the number of mobile devices located at the cell edge.
The inter-cell interference avoidance communication method according to claim 1. In the required bandwidth setting step, the required bandwidth is set based on the sum of the data rates of the mobile stations located at the cell edge,
The inter-cell interference avoidance communication method according to claim 1. In the required bandwidth setting step, the required bandwidth is set based on the amount of data in which the mobile device or the local station stays.
The inter-cell interference avoidance communication method according to claim 1. In the required bandwidth setting step, when a notification of communication quality equal to or higher than a predetermined communication quality is received from the mobile device, a required bandwidth greater than the required amount is set.
The inter-cell interference avoidance communication method according to any one of claims 1 to 4. In the required bandwidth setting step, a required bandwidth is set based on information acquired in the past for neighboring cells that have not received notification of communication quality equal to or higher than a predetermined communication quality from a mobile device.
The inter-cell interference avoidance communication method according to any one of claims 1 to 5. The information acquired in the past is information on reception quality with a neighboring cell that was reported when the mobile device connected in the past established a wireless connection,
The inter-cell interference avoidance communication method according to claim 6. The information acquired in the past is used as the communication quality and adjacent cell identification information when the mobile device connected in the past has notified the communication quality of a predetermined communication quality or higher.
The inter-cell interference avoidance communication method according to claim 6. The information acquired in the past is obtained from the handover history, and the information of the source cell of the mobile device that has been handed over to its own station,
The inter-cell interference avoidance communication method according to claim 6. The information acquired in the past is the information on the neighbor relationship of the cell acquired by the server from other base stations at the time of subchannel allocation, and is the information fed back from the server,
The inter-cell interference avoidance communication method according to claim 6. A communication system comprising a plurality of mobile devices, a plurality of base stations connectable to the mobile devices, and a server connected to the plurality of base stations,
Each mobile device
Measures the communication quality of the signal in the adjacent cell that is adjacent to the cell of the predetermined base station to which it is connected, and notifies the predetermined base station of the measured communication quality and the identification number of the adjacent cell And
The predetermined base station is
It is determined that the mobile device that has notified the communication quality equal to or higher than the predetermined communication quality is located at the cell edge of its own cell, and interferes with the neighboring cell based on the identification number of the neighboring cell received together with the communication quality. It is determined as a cell to be avoided,
Set the required bandwidth of the subchannel to be allocated to the mobile station located at the cell edge of the own cell, notify the server of the required bandwidth and the identification number of the interference avoidance target cell,
The server
Based on the identification number of the interference avoidance target cell received from each base station that is the predetermined base station and the required band, an interference graph is generated to solve the multiple coloring problem, and the frequency band of the cell is expressed by the number of colors. And sub-channels are associated with each color so that the sub-channel bandwidth is equal for each mobile device at the cell edge, and sub-channels corresponding to the number of mobile devices at the cell edge are assigned to each base station,
As a result of solving the multi-coloring problem, when a subchannel allocated to a specific base station can be used by a mobile station at a cell end or a non-cell end mobile station of a base station constituting another cell, Assign a subchannel assigned to the specific base station as a surplus subchannel to the base station constituting the another cell,
Notifying the assigned subchannel to each base station,
When the surplus subchannel is allocated, the surplus subchannel is notified to the base station configuring the another cell,
The predetermined base station is
Assign the subchannel notified from the server to the mobile station located at the cell edge of the own station,
When a surplus subchannel is notified from the server, the surplus subchannel is further allocated to a mobile device at a cell edge or a mobile device at a non-cell edge,
A communication system characterized by the above. The predetermined base station sets a required bandwidth based on the number of mobile devices located at the cell edge,
The communication system according to claim 11. The predetermined base station sets a required bandwidth based on a sum of data rates of mobile devices located at the cell edge,
The communication system according to claim 11. The predetermined base station sets a required bandwidth based on the amount of data in which the mobile device or the local station is retained,
The communication system according to claim 11. The predetermined base station sets a required bandwidth larger than a necessary amount when receiving a notification of communication quality higher than a predetermined communication quality from a mobile device,
The communication system according to any one of claims 11 to 14, characterized in that: The predetermined base station sets a required bandwidth based on information acquired in the past for neighboring cells that have not received notification of communication quality equal to or higher than the predetermined communication quality from the mobile device.
The communication system according to any one of claims 11 to 15, characterized in that: The information acquired in the past is information on reception quality with a neighboring cell that was reported when the mobile device connected in the past established a wireless connection,
The communication system according to claim 16. The information acquired in the past is used as the communication quality and adjacent cell identification information when the mobile device connected in the past has notified the communication quality of a predetermined communication quality or higher.
The communication system according to claim 16. The information acquired in the past is the information of the source cell of the mobile device that has been handed over to the local station obtained from the handover history,
The communication system according to claim 16. The information acquired in the past is the information on the neighbor relationship of the cell acquired by the server from other base stations at the time of subchannel allocation, and is the information fed back from the server,
The communication system according to claim 16.

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