JP2011055110A - Base station apparatus and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a base station apparatus, along with a communication method, for effectively using a wireless band, in a communication system performing the control for assignment of wireless resources of the wireless band. <P>SOLUTION: The base station apparatus determines combinations of available wireless resources in accordance with a constraint condition for assignment of wireless resources (RB). An evaluation index calculation unit 14 calculates, for every terminal station device, evaluation index values of combinations of available wireless resources (RB), on the basis of channel states of the wireless resources (RB). An optimum wireless resource allocation unit 15 selects combinations of wireless resources (RB) to be assigned to terminal station devices being targets of assignment, from among the combinations of available wireless resources (RB), in accordance with the evaluation index values. The optimum wireless resource allocation unit 15 selects the combinations of wireless resources (RB) satisfying a plurality of determined conditions, with respect to the combination optimization problem targeting all terminal station devices, which aims to maximize the sum total of the evaluation index values. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a base station apparatus and a communication method that effectively use a radio band in a communication system that performs control to allocate radio resources in the radio band.

  In wireless communication systems that use portable terminal station devices, standardization is progressing with the aim of realizing high-speed communication of 100 Mbps downlink (megabits per second) or more and 50 Mbps uplink or more with the direction from the base station device to the terminal station device being the downlink direction It has been. Among organizations that promote standardization, standardization organization 3GPP (Third Generation Partnership Project) is promoting standardization as an “LTE” (Long Term Evolution) system. In the LTE system, OFDMA (Orthogonal Frequency Division Multiple Access) is adopted as an LTE downlink access method in order to improve frequency utilization efficiency of radio communication. Also, in order to avoid high peak-to-average power ratio (PAPR), which is a drawback of OFDMA, in the uplink, SC-FDMA (single-carrier frequency-division multiple access) is adopted as an access method. Has been.

The wireless communication system is characterized by channel time fluctuation caused by movement of the terminal station apparatus and channel frequency fluctuation caused by multipath fading. In order to efficiently use precious radio bands, a wide frequency band is divided into subcarriers, and each subcarrier is time-divided into OFDM symbols (or SC-FDMA symbols) that are allocated to appropriate terminal stations according to the reception status. This method is considered effective. In other words, when there are a plurality of terminal station apparatuses, in order to obtain multiuser diversity gain, it is important to allocate time-frequency resources with good channel conditions to each terminal station apparatus. This resource allocation function is generally realized by a base station device arranged in a base station.
In the OFDMA or SC-FDMA base system, the minimum resource unit is a resource element. The definition of resource element is 1 OFDM symbol (or 1SC-FDMA symbol) × 1 subcarrier. In order to reduce the overhead of a control message for notifying a resource allocated to a terminal station apparatus, it is generally performed to group resource elements and use the group as a minimum allocation unit. For example, in LTE downlink / uplink, a resource element group of 14 OFDM symbols (or 14SC-FDMA symbols) × 12 subcarriers is defined as a resource block (RB). One RB is the minimum unit of resources allocated to the terminal station apparatus.

Further, in order to further reduce the overhead of the control message for notifying the RB assigned to the terminal station apparatus, the actual system places restrictions on the combination of RBs assigned to one terminal station apparatus. As an example, in the LTE downlink, three resource allocation types are defined, and only RB combinations that can be expressed using the three defined resource allocation types are assigned to the terminal station apparatus (see Non-Patent Document 2).
In addition, in the LTE uplink, there is a restriction that continuous RBs are allocated to the terminal station apparatus in order to maintain low PAPR.
As described above, it is required to efficiently use a valuable radio band in an OFDM or SC-FDMA based system under various constraints. Various packet scheduling methods have been proposed to effectively use the radio band. Among the proposed packet scheduling methods, the packet scheduling method based on Proportional Fairness (PF) (for example, see Non-patent Reference 3) keeps a good balance between the frequency utilization efficiency of the system and the fairness between terminal stations. Because it can be attracted attention.

3GPP TS 36.211 V8.7.0 (2009-5) 3GPP TS 36.213 V8.7.0 (2009-5) R. Padovani, A. Jalali, and R. Pankaj, “Data Throughput of CDMA HDR a High Efficiency-High Data Rate Personal Communication Wireless System,” Proceedings of IEEE Vehicular Technology Conference (VTC) Spring, July 2000, pp. 1854- 1858. F. D. Calabrese, C. Rosa, M. Anas, P. H. Michaelsen, K. I. Pedersen, P. E. Mogensen, “Adaptive Transmission Bandwidth Based Packet Scheduling for LTE Uplink,” Proceedings of IEEE Vehicular Technology Conference (VTC) 2008 Fall, September 2008. L. Temifio, G. Berardinelli, S. Frattasi and P. Mogensen, “Channel-Aware Scheduling Algorithms for SC-FDMA in LTE Uplink,” Proceedings of IEEE Personal Indoor and Mobile Radio Communication Conference (PIMRC), September 2008.

  However, the radio resource allocation by each PF scheduling method proposed so far including Non-Patent Reference 3 is a heuristic method, so it is limited to the local optimal solution, and the effective radio band by the global optimal solution is effective. There is a problem of not being used. As an example, in the PF scheduling method in LTE uplink shown in Non-Patent Reference 4 and Non-Patent Reference 5, attention is paid to an RB having a high PF evaluation index, and the RB is allocated to a terminal station apparatus. In the process of assigning RBs to the terminal station apparatus, only continuous RBs are set as allocation candidates, thereby taking into account the allocation constraints of continuous RBs. When continuously assigning RBs, changes in the channel state of the assigned RBs are not considered. For this reason, the packet scheduling methods shown in Non-Patent Reference 4 and Non-Patent Reference 5 have a problem in that it is not guaranteed that the assigned solution is an overall optimal solution.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a base station apparatus and a communication method that effectively use a radio band in a communication system that performs control to allocate radio resources in the radio band.

  In order to solve the above-described problem, the present invention provides a plurality of terminal station apparatuses with a radio resource of an allocation minimum unit defined based on a time axis and a frequency axis (in LTE, “RB (Radio Resource Block)”. ), A constraint condition providing unit that provides a constraint condition for the radio resource allocation, and an available RB combination determination that determines a combination of the radio resources that can be used according to the constraint condition A channel state data storage unit that stores, for each terminal station apparatus, a channel state corresponding to the minimum unit radio resource for allocation, and the determined available RB based on the stored channel state An evaluation index calculation unit that calculates an evaluation index value according to a combination, and an allocation to the terminal station apparatus to be allocated from among the available RB combinations RB combination is selected according to the evaluation index value, and is defined for the combination optimization problem for all the terminal station devices, which aims to maximize the sum of the evaluation index values. And a radio resource allocation unit that selects a combination of RBs to be allocated that satisfy a plurality of conditions. (Hereafter, the radio resource of the minimum unit for allocation is referred to as “RB (Radio Resource Block)”)

  Further, the present invention is the above-described invention, wherein the radio resource allocation unit does not transmit the uplink control channel information to the uplink of the radio link in the selection of the effective RB combination. Among the available RB combinations, the effective transmission effective according to the maximum transmission power of the terminal station apparatus, the change in the amount of transmittable data in the uplink, and the data queue length to be transmitted by the terminal station apparatus An RB combination selection unit that selects an RB combination for each terminal station apparatus.

  Further, the present invention is the above-described invention, wherein the radio resource allocating unit changes the transmittable data amount in the downlink with respect to the downlink of the radio link in the selection of the effective RB combination. And an effective RB combination selection unit that selects, for each terminal station apparatus, the effective RB combination that is effective according to the data queue length to be transmitted by the terminal station apparatus.

  Further, the present invention provides the evaluation index according to the invention described above, wherein the effective RB combination selection unit selects the effective RB combination according to a value Q predetermined as the number of effective RB combinations. The effective RB combinations corresponding to the top Q evaluation index values validated by the above are selected.

  Further, the present invention is the above-described invention, wherein the radio resource allocation unit allocates one set of the available RB combinations to at most one terminal station device, and at most one to each terminal station device. Assigning the available RB combinations, allocating all the RBs included in the set of available RB combinations to the specific terminal station apparatus to which the set of available RB combinations is assigned, Allocating one RB to at most one terminal station apparatus is defined as a constraint condition of the linear programming method.

  Also, in the present invention described above, in the above-described invention, the available RB combination determining unit selects, as the combination of RBs including continuous radio resources, for the uplink, and for the downlink The combination of RBs that can be expressed using resource allocation types 1, 2, and 3 is selected as a combination of available radio resources.

  Further, the present invention is a communication method for allocating a radio resource block (RB) defined based on a time axis and a frequency axis to a plurality of terminal station devices, wherein the radio resource is allocated. A constraint condition providing process for providing a constraint condition, an available RB combination determining process for determining an available RB combination according to the constraint condition, and a channel state corresponding to the RB are held for each terminal station apparatus From the channel state data storage process, the evaluation index calculation process for calculating the evaluation index value of the combination of RBs for each of the terminal station devices based on the held channel state, and the available RB combinations, The combination of the RBs is selected according to the evaluation index value for the terminal station device to be allocated, and the sum of the evaluation index values is maximized A radio resource allocation process for selecting a combination of radio resources satisfying a plurality of predetermined conditions for a combination optimization problem for all the terminal station devices, and a communication method comprising: is there.

  According to the present invention, in the base station apparatus, the constraint condition providing unit provides a constraint condition for radio resource allocation. The available RB combination determining unit determines a combination of radio resources (RB) that can be used in accordance with the constraint condition. The channel state data storage unit stores a channel state corresponding to a radio resource (RB) for each terminal station device. The evaluation index calculation unit calculates an evaluation index value for each terminal station apparatus according to a combination of available radio resources (RB) based on the held channel state. The radio resource allocating unit selects a combination of radio resources (RB) to be allocated to a terminal station apparatus to be allocated from among available radio resource (RB) combinations according to an evaluation index value, For a combination optimization problem for all terminal station devices that aims to maximize the sum of evaluation index values, a combination of radio resources that satisfy a plurality of defined conditions is selected.

  Thus, the present invention defines the packet scheduling problem as a combination optimization problem under various allocation constraints in OFDMA or SC-FDMA based systems, and allocates resources to terminal station devices based on effective RB combinations. To implement. It is possible to solve the defined combinatorial optimization problem and provide an overall optimal solution, so that valuable radio resources can be optimally used.

1 is a schematic block diagram illustrating a wireless communication system according to an embodiment of the present invention. It is a schematic block diagram which shows the structure of the radio | wireless frame control part 6 by this embodiment. It is a figure which shows the relationship between the system band and sub-frame in the uplink of the LTE system by this embodiment. It is a figure which shows the correspondence of the RB combination and RB which can be utilized by this embodiment. It is a graph which shows the simulation result of the cell throughput by this embodiment. It is a graph which shows the simulation result of the cell coverage by this embodiment. It is a figure which shows the allocation condition of the resource block group in the resource allocation type 1 by this embodiment. It is a figure which shows the correspondence of the RB combination and RB which can be utilized by this embodiment. It is a figure which shows the example which divided | segmented RBG by this embodiment into a subset. The correspondence relationship of each RB combination and RB of the resource allocation type 2 by this embodiment is shown.

An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic block diagram showing a wireless communication system in the present embodiment.
The wireless communication system 10 includes a base station device 1 and a terminal station device 9.
The base station apparatus 1 communicates with a plurality of terminal station apparatuses 9 existing in a service area that provides communication. The radio link used for communication between the base station device 1 and the terminal station device 9 is based on, for example, an LTE (Long Term Evolution) system. In the wireless link, communication from the base station apparatus 1 to the terminal station apparatus 9 is defined as downlink, and communication in the opposite direction is defined as uplink.
The base station apparatus 1 shown in this embodiment optimizes radio resource allocation in this radio link. The allocation of radio resources is optimized based on the minimum unit radio resources for allocation (hereinafter referred to as “RB”).

The base station apparatus 1 includes packet buffers 2 and 5, an OFDMA transmission unit 3, an SC-FDMA reception unit 4, and a radio frame control unit 6.
The packet buffer 2 temporarily holds a packet to be transmitted to the terminal station device 9 and adjusts the timing to transmit as a transmission packet.
The OFDMA transmission unit 3 performs a framing process for generating a radio link frame, a process for allocating and transmitting a transmission packet supplied from the packet buffer 2, a process for generating an OFDM signal, and the like. The OFDMA transmission unit 3 selects a radio resource in the radio frame according to an instruction from the radio frame processing unit 6, allocates transmission packet data using the selected radio resource, and transmits the data.
The OFDMA transmission unit 3 transmits the control information notified from the radio frame processing unit 6 to the terminal station device 9 using the selected radio resource. The notified control information includes radio resource allocation information in the radio frame.

The SC-FDMA reception unit 4 demodulates the SC-FDMA signal received from the terminal station device 9, selects a radio resource allocated to the radio frame according to an instruction from the radio frame processing unit 6, and selects the radio resource. The received signal is extracted and converted into a packet signal.
The packet buffer 5 temporarily holds the packet received from the terminal station device 9 and adjusts the timing at which the received packet is transferred.

The radio frame control unit 6 includes a DL control unit 6D and a UL control unit 6U, manages radio resources in the radio link transmitted and received by the base station apparatus 1, and uses the OFDMA transmission unit to effectively use the limited radio resources. 3 and the SC-FDMA receiver 4 are notified to the terminal station device 9 of the radio resource allocation status.
The DL control unit 6D manages downlink radio resources in the radio link and controls the OFDMA transmission unit 3.
The UL control unit 6U manages uplink radio resources in the radio link and controls the SC-FDMA reception unit 4.

Configurations of the DL control unit 6D and the UL control unit 6U will be described with reference to the drawings.
FIG. 2 is a schematic block diagram showing the configuration of the radio frame control unit 6.
The radio frame controller 6 shown in the figure shows only one system, that is, one of the DL controller 6D or the UL controller 6U, without distinguishing between downlink and uplink.
The radio frame control unit 6 includes a constraint condition providing unit 11, an available RB combination determining unit 12, a channel state data storage unit 13, an evaluation index calculation unit 14, and an optimal radio resource allocation unit 15.

The constraint condition providing unit 11 provides a constraint condition for radio resource allocation in the downlink or uplink. As an example, the constraint condition providing unit 11 provides the available RB combination determining unit 12 with a constraint condition for assigning consecutive RBs in the uplink.
The available RB combination determining unit 12 selects the available RB combinations for all terminals in accordance with the constraint condition provided from the constraint condition providing unit 11.
The channel state data storage unit 13 holds, for each terminal station device 9, the channel state corresponding to the RB defined based on the time axis and the frequency axis.

  The evaluation index calculation unit 14 calculates an evaluation index value for each available RB combination based on the channel state for each terminal station device 9 acquired from the channel state data storage unit 13 and provides it to the optimal radio resource allocation unit 15 To do. For example, in a system for the purpose of maximizing the frequency utilization efficiency, the evaluation index is the frequency utilization efficiency, and the evaluation index calculation unit 14 converts the channel state into the frequency utilization efficiency. Further, in a system aiming to maintain a good balance between the frequency utilization efficiency and the fairness trade-off between the terminal station devices 9, the evaluation index is a Proportional Fairness (PF) index, and the evaluation index calculation unit 14 determines from the channel state. The ratio of the estimated instantaneous transmission rate and the average transmission rate of the terminal station device 9 based on the radio resource allocation results so far is calculated.

The optimum radio resource allocating unit 15 evaluates a combination of radio resources satisfying a plurality of conditions defined as a combination optimization problem for optimal use of radio resources based on the selected available RB combination. Select according to the value.
The optimal radio resource allocating unit 15 defines the radio resource allocation problem as a combinatorial optimization problem, obtains an optimal solution for the combinatorial optimization problem from linear programming, and uses the radio resources optimally. Specifically, the optimal radio resource allocating unit 15 defines maximization of the evaluation index as an objective function of the combination optimization problem, and the effective RB determined for each terminal station device 9 from the available RB combinations. Based on the evaluation index of the combination (determination method will be described later), an optimal resource allocation solution is obtained by linear programming.

  That is, the optimal radio resource allocation unit 15 selects an RB combination to be allocated to the allocation target terminal station device 9 from the available RB combinations according to the evaluation index value. For a combination optimization problem for all terminal station devices 9 for the purpose of maximizing the sum of values, a combination of radio resources satisfying a plurality of defined conditions is selected.

The optimal radio resource allocation unit 15 includes an effective RB combination determination unit 16 and an optimal resource allocation calculation unit 17.
The effective RB combination determination unit 16 determines an effective RB combination for each terminal station device 9 in the radio resource allocation unit 15. The effective RB combination for each terminal station device 9 by the effective RB combination determining unit 16 is the terminal station device 9 of the available RB combinations derived from the available RB combination determining unit 12 for all terminals. RB combinations that can be assigned to
The optimal resource allocation calculation unit 17 performs optimal resource allocation in the radio resource allocation unit 15 using linear programming. In the linear programming method by the optimal resource allocation calculation unit 17, RB combinations other than effective RB combinations are not allocated to the terminal station device 9 among the available RB combinations. In other words, the optimal radio resource allocating unit 15 is configured to allocate combinations of RBs that satisfy a plurality of conditions defined as a combination optimization problem for optimal use of radio resources based on the selected combination of available radio resources. Is selected according to the evaluation index value. Further, in order to reduce the calculation amount of the linear programming method, an effective RB combination upper limit value for each terminal station device 9 may be determined in advance.

  In the following, an embodiment will be described by taking as an example optimal packet scheduling in an SC-FDMA-based uplink of an LTE system and optimal packet scheduling in an OFDMA-based downlink.

First, the embodiments will be described by defining the following terms.
“Terminal i” is indicated by using Indexi for identifying each of the plurality of terminal station devices 9.
A “subframe” is a minimum unit of radio resource allocation on the time axis, and in the LTE system, 14 OFDM symbols and 14SC-FDMA symbols are defined as subframes. The radio resource block is identified by the index of the subframe on the time axis (referred to as “subframe index j”) and the index of the RB (consisting of 12 subcarriers) on the frequency axis (referred to as “RB Index k”). Is done.

 “RB allocation result A (i, j, k)” indicates a radio resource allocation result referred to by subframe Index j and RB Index k for terminal i. A (i, j, k) = 1 indicates that radio resources referred to by subframes Index j and RB Index k are allocated to terminal i. On the other hand, A (i, j, k) = 0 indicates that radio resources referred to by subframes Index j and RB Index k are not allocated to terminal i. The RB allocation result A (i, j, k) can be expressed as Equation (1) because there is a restriction that the resources allocated to the terminals are orthogonal. That is, one RB is allocated to at most one terminal.

“Available RB combination set O” is a set having available RB combinations as elements, which are derived based on the system bandwidth and allocation constraint conditions.
“Index l of available RB combination” indicates an index for identifying an RB combination included in the set O of available RB combinations. The RB combination indicated by Index l of the available RB combinations is indicated as “RB combination l”.
“Inclusive relation V (k, l) of RB and available RB combination” is V (k, l) = 1 when RB k is included in RB combination l. If RB k is not included in the RB combination l, V (k, l) = 0.
The “number of RBs included in the available RB combination l” is N (l).

“RB combination allocation result α (i, j, l)” is the allocation result of subframe Index j and RB combination Index l for terminal i. α (i, j, l) = 1 indicates that an RB included in subframe Index j and RB combination Index l is allocated to terminal i. On the other hand, α (i, j, l) = 0 indicates that the RB included in subframe Index j and RB combination Index l is not allocated to terminal i. Σ _i α (i, j, l) = 0 or 1 due to the restriction that radio resources allocated to terminals are orthogonal. That is, at most one RB combination is assigned to one terminal. In addition, since resource allocation is performed on an RB combination basis, it can be expressed as equation (2). That is, at most one RB combination is assigned to one terminal.

“PF index M (i, j, l)” indicates a PF index in a radio resource in which terminal i has subframe Index j and RB combination Index l.
The “assignment target terminal set Ω (j)” is a set having the index of the assignment target terminal as an element in the subframe Index j.
The “assignable RB Index set P (j)” is a set of RB Indexes that can be assigned to data in the subframe Index j.
“Effective RB combination set C (i, j) for terminal i” is a set whose elements are effective RB combinations for terminal i in subframe Index j and is a subset of set O.

[1] Application of LTE System to Uplink First, the optimum packet scheduling in the uplink of the LTE system will be described.
The uplink access scheme of the LTE system is SC-FDMA.
In the packet scheduling in this SC-FDMA based system, there is a constraint that assigns continuous RBs to terminals in order to maintain low PAPR.
FIG. 3 is a diagram illustrating a relationship between a system band and a subframe in the uplink of the LTE system.

In this figure, the vertical axis indicates the system band in units of RB, and the horizontal axis indicates the subframe.
This figure shows an example in which the system band is 11 RBs, and RBs from RB0 to RB10 are shown. Also, subframes indicated as subframes Index0 to subframe Index j are continuously shown in the time axis (horizontal axis) direction. Hereinafter, assuming that the system band is 11 RBs, the usable RB combination set O and the indexes and V (k, l) of the usable RB combinations will be described.

  When the number of RBs included in the usable RB combination is indicated by X, X takes a value from “1” to “system band RB count K”. In the usable RB combinations, since there is a restriction that RBs are continuously arranged, the number of usable RB combinations including X RBs is (K−X + 1). The number of all available RB combinations from “1” to “system band RB count K” is shown in Equation (3).

  Therefore, the available RB combination Index l takes a value in the range shown in Expression (4).

  Here, assuming that the available RB combination Indexl is given in ascending order of the number of RBs included in the combination, the available RB combination Indexl including X 'RBs is a value in the range shown in Equation (5). Take.

The inclusion relation between RB and available RB combination is expressed using V (k, l) indicating the inclusion relation between RB and available RB combination.
FIG. 4 is a diagram illustrating a correspondence relationship between available RB combinations and RBs.
FIG. 4A shows, as an example, a correspondence relationship between RBs assigned when each available RB combination is X ′ = 1. In this figure, since there is one RB included in the usable RB combination, one RB is allocated for each usable RB combination Index1.
For example, when the available RB combination Index1 is “0”, the assigned RB is indicated as k = 0.
The available RB combination Index1 shown in this figure takes a value from 0 to 10.

FIG. 4B shows, as an example, the correspondence relationship between RBs assigned when each available RB combination is X ′ = 5.
Since there are five RBs included in the usable RB combination, five RBs are continuously allocated for each usable RB combination Index1.
For example, when the available RB combination Index1 is “38”, the allocated RBs are indicated as k = 0 to k = 4.
This figure is shown by the available RB combinations Index1 given continuously from the range of the available RB combinations Index1 shown in FIG. 4 (a), and the available RB combinations Index1 are from 38 to 44. Takes a value.

In subframe Index j, effective set RB combinations C (i, j) for terminal i are different. The set O of the available RB combinations is defined by the system bandwidth and the allocation restriction of consecutive RBs in the uplink, whereas the set C (i, j) is the RB Index for uplink control channel transmission in the subframe Index j. , Defined by the maximum transmission power and channel state of terminal i.
Of all the RB combinations in the set of available RB combinations, the RB combination l that satisfies the following condition is not included in the set C (i, j).

(1) RB combination including the RB Index assigned to the control channel
As an example, in the subframe Index j, it is assumed that RBs (RB0 and RB10) at both ends of 11RBs are uplink control channel RBs. That is, the Index of RB assigned to data is 1-9. Therefore, among the RB combinations with X ′ = 1, the relationship shown as Expression (6) holds for l = 0 and l = 10.

  In addition, among the RB combinations of X ′ = 5, the relationship shown as Expression (7) holds for l = 38 and l = 44.

(2) RB combination exceeding the maximum transmission power of terminal i
For example, when the maximum number of RBs that can be transmitted is 5 at the maximum transmission power limit of the terminal i, 6 or more RBs are not allocated, and therefore, Formula (8) is used.

 (3) When the transmittable data amount (TBS: Transport Block Size) of the RB combination l is smaller than the transmittable data amount of the RB combination that is a subset of the RB combination l, Equation (9) is established.

Here, TBS depends on an average channel state in RB combination l. If the allocated RB is expanded in the state where the channel condition in the frequency band due to multipath fading has occurred, the RB with reduced propagation characteristics will also be used, which may reduce the amount of transmittable data. is there.
(4) When the transmittable data amount of the RB combination which is a subset of the RB combination l is larger than the data queue length to be transmitted by this terminal, the expression (10) is established.

Using the above definition, the combinatorial optimization problem is defined as follows.
The objective function of the combinatorial optimization problem is shown in Equation (11). The objective function for maximizing the PF evaluation index here is an example. If the objective function is to minimize or maximize other evaluation indices, the following optimization formula can be easily ported.

Objective function:

  The constraint conditions for the combinatorial optimization problem are shown in equations (12) to (19).

Restrictions:
Subject to:

Each expression of the above constraint conditions will be described in order below.
In Equation (12), the left side of the equation is an assignment result managed in units of RBs, and indicates the number of RBs assigned to terminal i. Further, the right side of the equation is an allocation result managed in units of RB combinations, and similarly indicates the number of RBs allocated to terminal i. That is, Equation (12) indicates that, when RB combination Index i is allocated to a certain terminal, all RBs included in RB combination Index i are allocated to that terminal.
Equation (13) indicates that one RB combination is assigned to at most one terminal.
Equation (14) indicates that at most one RB combination is allocated to one terminal.
Equation (15) indicates that one RB is allocated to at most one terminal.
Equation (16) indicates that the number of RBs assigned to the terminal is less than or equal to the number of RBs in the system band.
Expression (17) indicates that the allocation result of the RB combinations included in the effective RB combination set C (i, j) for the terminal i is 0 (not allocated) or 1 (allocated).
Equation (18) indicates that the assignment result of RB Index k for terminal i is 0 (not assigned) or 1 (assigned).
Equation (19) indicates that the allocation result of RB combinations not included in the valid RB combination set C (i, j) for terminal i is 0 (not allocated).

  In addition, in order to reduce the amount of calculation of linear programming, the number of effective RB combinations to be developed in linear programming is limited for each terminal. That is, for all terminals, only the top Q effective RB combinations of the evaluation indices are expanded to linear programming. If the Q-th evaluation index of the terminal i is expressed by δ (i), this constraint condition is expressed using the equation (20).

  When formulas (11) to (20) are developed in the linear programming method, an optimal solution of the combinatorial optimization problem is obtained.

The cell throughput evaluated based on the conditions shown as an example and the cell coverage (5% outage average user throughput is used as a coverage evaluation index) result are shown.
FIG. 5 is a graph showing a simulation result of cell throughput.
The vertical axis represents cell throughput (kbps (kilobits per second)), and the horizontal axis represents the number of terminals per cell.
In this simulation, Q is 91 when the number of terminals per cell is 10, and Q is 45 when the numbers of terminals per cell are 15 and 20.

FIG. 6 is a graph showing a simulation result of cell coverage.
The vertical axis represents cell coverage (kbps), and the horizontal axis represents the number of terminals per cell.
In this simulation, Q is 91 when the number of terminals per cell is 10, and Q is 45 when the numbers of terminals per cell are 15 and 20.

  5 and 6 show that the optimum packet scheduling (OPSA: Optimum Packet Scheduling Algorithm) by the method shown in this embodiment and the heuristic packet scheduling (HPSA: Heuristic Packet Scheduling Algorithm) by the conventional method are shown in the evaluation results by the simulations of FIGS. Compare. Optimal packet scheduling (OPSA) by the method shown in this embodiment is shown to be more effective in improving cell throughput and cell coverage than heuristic packet scheduling (HPSA), and optimal radio resource allocation is performed. I understand that.

[2] Application of LTE system to OFDMA-based downlink Next, optimum packet scheduling in the OFDMA-based downlink of the LTE system will be described.
Similar to the optimal packet scheduling applied to the uplink, the optimal packet scheduling in the downlink will be described below.
In the downlink of the LTE system, the available RB combination determining unit 12 can be applied to three resource allocation types indicated as resource allocation types 1, 2, and 3. The following shows the application to the resource allocation type that will be written in order.

<Application to resource allocation type 1>
In the RB allocation in the resource allocation type 1, the available RB combination determination unit 12 allocates radio resources to terminals in units of resource block groups (RBG) configured by a plurality of RBs. However, the number of RBs included in the RBG depends on the system bandwidth. As an example, the system band is 11 RBs, and the allocated RBG is composed of two RBs.
FIG. 7 is a diagram showing a resource block group allocation situation in the resource allocation type 1.
As shown in this figure, in the case of an RBG composed of two RBs, six RBGs are defined. However, since the system band is 11 RBs, only RBG6 is composed of one RB.

  That is, the number of available RB combinations that can be expressed using resource allocation type 1 is 63 as shown in Equation (21).

An example of an available RB combination composed of 1RBG and 2RBG is shown with reference to the figure.
FIG. 8 is a diagram illustrating a correspondence relationship between available RB combinations and RBs.
The setting of the Index of the available RB combination shown in this figure is an example.
In this figure, the available RB combinations Index l = 0 to l = 5 show an example in which one BRG is allocated, and the available RB combinations Index l = 6 to l = 20 are examples in which two BRGs are allocated. Indicates.

<Application to resource allocation type 2>
In the RB allocation in the resource allocation type 2, the available RB combination determining unit 12 further manages the RBG by dividing it into subsets. However, the number of subsets that can be divided depends on the system bandwidth.
FIG. 9 is a diagram illustrating an example in which the RBG is divided into subsets.
The RBG division example shown in this figure is a subset configuration example when the system band is 11 RBs and divided into two subsets.
FIG. 9A shows the allocation of the RBG before the division, RBG1 is RB0 and RB1, RBG2 is RB2 and RB3, RBG3 is RB4 and RB5, RBG4 is RB6 and RB7, RBG5 is RB8 and RB9 RB10 is assigned to RBG6. Divide this allocation into two subsets.
FIG. 9B shows a first RBG subset (RBG subset1). Three RBGs are allocated to the first RBG subset. In the RBG assigned to the first RBG subset, RB0 and RB1 are assigned to RBG1, RB4 and RB5 are assigned to RBG3, and RB8 and RB9 are assigned to RBG5.
FIG. 9C shows a second RBG subset (RBG subset2). Three RBGs are also allocated to the second RBG subset. In the RBG assigned to the second RBG subset, RB2 and RB3 are assigned to RBG2, RB6 and RB7 are assigned to RBG4, and RB10 is assigned to RBG6.

  When resource allocation type 2 is used, RBs in the same subset can be allocated for each terminal. The number of available RB combinations that can be expressed using the resource allocation type 2 is the number of combinations shown in Expression (22).

FIG. 10 shows the correspondence between each available RB combination of resource allocation type 2 and the RB.
In the example shown in the figure, an available RB combination composed of 2 RBs is shown as an example.
Note that, in resource allocation type 2, there are some that overlap with the available RB combinations of resource allocation type 1. In the available RB combinations shown in this figure, those that overlap with the available RB combinations of resource allocation type 1 are not shown. The available RB combination Index shown here is an example.

<Application to resource allocation type 3>
In RB allocation in resource allocation type 3, continuous RBs are allocated for each terminal. That is, it is the same as the restriction in the uplink shown above. For examples of available RB combinations that can be expressed using resource allocation type 3, refer to FIG. 4 described above.

  It is assumed that among all RB combinations in the available RB combination set, the RB combination l that satisfies the following conditions is not included in the set C (i, j).

(1) When the transmittable data amount (TBS: Transport Block Size) of the RB combination l is smaller than the transmittable data amount of the RB combination that is a subset of the RB combination l, the relationship shown in Expression (23) is established. The relationship is the same as that of the uplink shown above.

(2) When the transmittable data amount of the RB combination which is a subset of the RB combination l is larger than the data queue length to be transmitted by this terminal, the relationship shown in Expression (24) is established. The relationship is the same as that of the uplink shown above.

  After obtaining an effective RB combination for each terminal, as shown in the uplink case, a combination optimization problem is defined, and the optimal resource allocation calculation unit 17 solves the combination optimization problem by linear programming. Lead. For details, reference is made to equations (11) to (20).

The present invention is not limited to the above embodiments, and can be modified without departing from the spirit of the present invention.
Although the solution of the combinatorial optimization problem performed by the optimal resource allocation calculation unit 17 has been shown as being derived by linear programming, other methods such as dynamic programming can be applied.
Further, the system bandwidth, radio resource allocation method, and definition of each index shown in this embodiment are merely examples, and other forms are possible.
In addition, although the application of the present embodiment has been exemplified by applying to the LTE system, the application to other systems is also possible.

In the base station apparatus 1 of the present embodiment, the constraint condition providing unit 11 provides a constraint condition for radio resource allocation. The available RB combination determination unit 12 determines a combination of available radio resources (available RB combination) according to the constraint condition. The channel state data storage unit 13 holds the channel state corresponding to the RB for each terminal station device. The evaluation index calculation unit 14 calculates an evaluation index value of an available RB combination for each terminal station apparatus 9 based on the held channel state. The optimal radio resource allocating unit 15 selects an RB combination to be allocated to the allocation target terminal station device 9 from the available radio resource combinations according to the evaluation index value. For the combination optimization problem for all the terminal station devices 9 for the purpose of maximizing the sum of the radio resources, a combination of radio resources satisfying a plurality of predetermined conditions is selected.
As a result, radio resources can be allocated based on a plurality of conditions indicated as the combination optimization problem, and the radio band can be used effectively.

Also, in the optimal radio resource allocation unit 15 of the present embodiment, the effective RB combination selection unit 16 transmits uplink control channel information to the uplink of the radio link when selecting an effective RB combination. Among the combinations of radio resources not to be used, combinations of radio resources that are effective according to the maximum transmission power of the terminal station device 9, the change in the amount of transmittable data in the uplink, and the data queue length to be transmitted by the terminal station device 9 Is selected for each terminal station device 9.
As a result, for example, the LTE system can be applied to the uplink, and the radio band can be used effectively.

Also, the optimal radio resource allocation unit 15 of the present embodiment is such that the effective RB combination selection unit 16 changes the transmittable data amount in the downlink with respect to the downlink of the radio link in the selection of the effective RB combination. And, a combination of effective radio resources according to the data queue length to be transmitted by the terminal station device 9 is selected for each terminal station device 9.
Thereby, for example, the LTE system can be applied to the downlink, and the radio band can be used effectively.

Further, the available RB combination determination unit 12 according to the present embodiment selects the top Q evaluations that are validated by the evaluation index according to a value Q that is predetermined as the number of valid RB combinations in the selection of valid RB combinations. Select a valid RB combination corresponding to the index value.
As a result, it is possible to reduce the arithmetic processing by limiting the number of effective RB combinations that are candidates for the solution of the optimization problem, so that the solution of the combination optimization problem can be easily derived. Therefore, the wireless band can be used effectively.

The optimal radio resource allocating unit 15 of the present embodiment allocates one set of RB combinations to at most one terminal station device 9, assigns at most one RB combination to one terminal station device 9, and sets one set. All RBs included in one set of RB combinations are allocated to the specific terminal station device 9 to the specific terminal station device 9 to which one RB combination is allocated, and one RB is assigned to at most one terminal station device 9 Assigning is defined as a condition of the combinatorial optimization problem.
Thus, by indicating a plurality of conditions indicated as the combination optimization problem, a solution is derived from the conditions of the combination optimization problem, so that the radio band can be used effectively.

In addition, the effective RB combination selection unit 16 of the present embodiment selects an RB combination including consecutive RBs for the uplink, and uses resource allocation types 1, 2, and 3 for the downlink. A combination of RBs that can be expressed is selected as a combination of available RBs.
Thereby, it can optimize in the allocation of the radio | wireless resource of the radio link applied to a LTE system, and can utilize a radio | wireless band effectively.

6 Radio frame control unit 11 Restriction condition providing unit 12 Available RB combination determining unit 13 Channel state data storing unit 14 Evaluation index calculating unit 15 Optimal radio resource allocating unit 16 Effective RB combination determining unit 17 Optimal resource allocation calculating unit

Claims (7)

A base station apparatus that allocates radio resources in a minimum unit for allocation defined based on a time axis and a frequency axis to a plurality of terminal station apparatuses,
A constraint condition providing unit for providing a constraint condition of the radio resource allocation;
An available RB combination determining unit that determines a combination of the radio resources that can be used in accordance with the constraint condition;
A channel state data storage unit that holds, for each terminal station device, a channel state corresponding to the radio resource of the minimum unit for allocation;
An evaluation index calculation unit that calculates an evaluation index value of the combination of available radio resources for each of the terminal station devices based on the state of the held channel;
A combination of radio resources to be allocated to the terminal station apparatus to be allocated is selected from the combinations of available radio resources according to the evaluation index value, and the sum of the evaluation index values is maximum. A radio resource allocation unit that selects a radio resource combination of the minimum unit for allocation satisfying a plurality of predetermined conditions for a combination optimization problem for all the terminal station devices, ,
A base station apparatus comprising: The radio resource allocation unit
In the selection of the effective radio resource combination of the minimum unit for allocation, among the radio resource combinations that do not transmit the uplink control channel information to the uplink of the radio link communicating with the terminal station apparatus From the maximum transmission power of the terminal station apparatus, the change in the amount of transmittable data in the uplink, and the combination of the minimum unit radio resources that are effective according to the data queue length to be transmitted by the terminal station apparatus An effective RB combination selection unit for selecting for each terminal station device,
The base station apparatus according to claim 1, comprising: The radio resource allocation unit
In the selection of the effective radio resource combination of the minimum unit for allocation, a change in the amount of transmittable data in the downlink and a data queue to be transmitted by the terminal station apparatus with respect to the downlink of the radio link An RB combination selection unit that selects, for each of the terminal station devices, an effective combination of radio resources according to length
The base station apparatus according to claim 1, further comprising: The effective RB combination selection unit is:
In the selection of the effective radio resource combination, according to the value Q predetermined as the number of effective radio resource combinations, the top Q corresponding to the evaluation index values enabled by the evaluation index The base station apparatus according to any one of claims 1 to 3, wherein an effective radio resource combination is selected. The radio resource allocation unit
Allocating one set of the minimum unit radio resource combinations for allocation to at least one terminal station device;
Allocating at least one combination of radio resources in the minimum unit for allocation to one terminal station apparatus;
All the minimum units for allocation included in the combination of the minimum radio units for allocation to the specific terminal station apparatus to which the combination of the minimum radio units for allocation is allocated. Allocating radio resources,
The base station apparatus according to any one of claims 1 to 4, wherein allocation of the one radio resource to at most one terminal station apparatus is defined as a condition of the combination optimization problem. The available RB combination determining unit
For the uplink, select as a combination of the radio resources including continuous radio resources,
The radio resource combination that can be expressed using resource allocation types 1, 2, and 3 for the downlink is selected as a combination of available radio resources. The base station apparatus as described in. A communication method for allocating radio resources in a minimum unit for allocation defined based on a time axis and a frequency axis to a plurality of terminal station devices,
A constraint condition providing process for providing a constraint condition when allocating the radio resource;
An available RB combination determination process for determining a combination of the radio resources that can be used according to the constraints;
A channel state data storage process for holding a channel state corresponding to a radio resource for each of the terminal station devices;
An evaluation index calculation process for calculating an evaluation index value of the combination of available radio resources for each of the terminal station devices based on the state of the held channel;
A combination of radio resources to be allocated to the terminal station apparatus to be allocated is selected from the combinations of available radio resources according to the evaluation index value, and the sum of the evaluation index values is maximum. A radio resource allocation process for selecting a combination of the radio resources satisfying a plurality of predetermined conditions for a combination optimization problem for all the terminal station devices,
A communication method comprising:

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