WO2010101111A1 - 移動通信システムで使用される基地局装置及び方法 - Google Patents
移動通信システムで使用される基地局装置及び方法 Download PDFInfo
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- WO2010101111A1 WO2010101111A1 PCT/JP2010/053239 JP2010053239W WO2010101111A1 WO 2010101111 A1 WO2010101111 A1 WO 2010101111A1 JP 2010053239 W JP2010053239 W JP 2010053239W WO 2010101111 A1 WO2010101111 A1 WO 2010101111A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/50—Allocation or scheduling criteria for wireless resources
- H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/0001—Arrangements for dividing the transmission path
- H04L5/0003—Two-dimensional division
- H04L5/0005—Time-frequency
- H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0037—Inter-user or inter-terminal allocation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0058—Allocation criteria
- H04L5/006—Quality of the received signal, e.g. BER, SNR, water filling
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0058—Allocation criteria
- H04L5/0075—Allocation using proportional fairness
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/50—Allocation or scheduling criteria for wireless resources
- H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
- H04W72/542—Allocation or scheduling criteria for wireless resources based on quality criteria using measured or perceived quality
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0058—Allocation criteria
- H04L5/0064—Rate requirement of the data, e.g. scalable bandwidth, data priority
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0078—Timing of allocation
- H04L5/0085—Timing of allocation when channel conditions change
Definitions
- the present invention relates to the technical field of mobile communication, and more particularly to a base station apparatus and method used in a mobile communication system using next-generation mobile communication technology.
- Super3G has been created as Long Term Evolution (LTE) by the standard organization 3GPP (3rd Generation Partnership Project) of W-CDMA (Wideband-Code Division Multiple Access).
- LTE Long Term Evolution
- W-CDMA Wideband-Code Division Multiple Access
- HSPA High Speed Packet Access
- the downlink radio access method in LTE is an orthogonal frequency division multiple access (OFDMA) method.
- OFDMA orthogonal frequency division multiple access
- SC-FDMA Single-Carrier Frequency Division Multiple Access
- the OFDMA system is a multi-carrier transmission system in which a frequency band is divided into a plurality of narrow frequency bands (subcarriers) and data is transmitted on each subcarrier. It can be expected that high-speed transmission can be realized by increasing the frequency utilization efficiency by arranging subcarriers densely while being orthogonal to each other on the frequency axis.
- the SC-FDMA scheme is a single carrier transmission scheme that divides a frequency band for each terminal and transmits using a different frequency band among a plurality of terminals.
- the SC-FDMA scheme is preferable from the viewpoint of reducing power consumption of terminals and expanding coverage.
- LTE-Advanced Long Term Evolution-Advanced
- the radio access method is the same between the LTE system and the LTE-Advanced system.
- LTE-Advanced also employs OFDMA as the downlink radio access method.
- communication is performed by allocating one or more resource blocks (RB: Resource Block) or resource units (RU: Resource Unit) to the user apparatus in both downlink and uplink.
- RB Resource Block
- RU Resource Unit
- resource blocks in the downlink are represented by a time domain and a frequency domain.
- a resource block is represented by a resource grid with N RB DL N sc RB subcarriers and N symb DL OFDM symbols.
- N RB DL is a downlink bandwidth represented by a plurality of N sc RBs . 6 ⁇ N RB DL ⁇ 110 is satisfied.
- N sc RB is a resource block size in the frequency domain represented by a plurality of subcarriers.
- N symb DL is the number of OFDM symbols included in the downlink slot.
- the time domain resolution is 1 ms and the frequency domain resolution is 180 kHz.
- the resource unit in the uplink is represented by the time axis and the frequency axis as in the downlink.
- a resource unit is represented by a resource grid with N RB UL N sc RB subcarriers and N symb UL SC-FDMA symbols.
- N RB UL is the uplink bandwidth represented by a plurality of N sc RBs . 6 ⁇ N RB UL ⁇ 110 is satisfied.
- N sc RB is a resource block size in the frequency domain expressed as a plurality of subcarriers.
- N symb UL is the number of SC-FDMA symbols included in the uplink slot.
- the time domain resolution is 1 ms and the frequency domain resolution is 180 kHz.
- resource block and resource unit are used as synonyms, and both indicate units of resource allocation.
- Resource blocks are shared by multiple user devices in the system.
- one resource block has a bandwidth of 180 kHz.
- a system band of 5 MHz includes 25 resource blocks.
- the base station apparatus determines, for example, which user apparatus among a plurality of user apparatuses to allocate a resource block for each subframe (Sub-frame) that is 1 ms in LTE.
- the subframe may be called a transmission time interval (TTI).
- TTI transmission time interval
- the determination of radio resource allocation is called scheduling.
- the base station apparatus transmits a shared channel using one or more resource blocks to the user apparatus selected by scheduling.
- the shared channel is called a physical downlink shared channel (PDSCH: Physical Downlink Shared CHannel).
- the user apparatus selected by scheduling transmits a shared channel to the base station apparatus using one or more resource blocks.
- This shared channel is called a physical uplink shared channel (PUSCH: Physical Uplink Shared CHannel).
- the control channel used for this signaling is called a physical downlink control channel (PDCCH: Physical Downlink Control CHannel) or a downlink L1 / L2 control channel (DL-L1 / L2 Control Channel).
- the downlink control signal may include a physical control format indicator channel (PCFICH: Physical Control Format Indicator CHannel), a physical hybrid ARQ indicator channel (PHICH: Physical Hybrid ARQ Indicator CHannel), etc., in addition to the PDCCH. .
- 1-cell repetition is applied in LTE and LTE-Advanced.
- the same frequency channel can be used in adjacent cells.
- OFDMA is adopted, so that each user is orthogonal in the cell.
- each user since each user is orthogonal in the cell, there is no mutual interference between users.
- the same frequency channel is used in adjacent cells, when similar subcarriers are also used in adjacent cells, they receive interference from adjacent cells.
- a signal received from a base station where a user located at a cell edge (boundary) is located is interfered by a signal from an adjacent base station adjacent to the base station.
- Throughput is reduced by receiving interference from a signal from an adjacent base station.
- the frequency that can be used at the cell edge is set in advance for each cell.
- the frequency band that can be allocated differs between the cell edge region and the region other than the cell edge region.
- the system band is divided into a plurality of parts. Among the divided system bands, the user equipment located in the cell edge area of a certain cell and the user equipment located in the cell edge area of an adjacent cell adjacent to the certain cell Of these, different frequency bands are allocated.
- FIG. 1 shows an example of frequency band allocation in FFR.
- the horizontal axis represents frequency
- the vertical axis represents transmission power of the base station.
- FIG. 1 shows an example of FFR in which 3-cell repetition is applied to a user located at a cell edge for ease of explanation.
- the system band is divided into three.
- a frequency band obtained by dividing the system band is referred to as a divided frequency band.
- Frequency bands including the same division frequency band are assigned to user apparatuses located in areas other than the cell edge areas of cell 1, cell 2, and cell 3.
- the user equipment located in the cell edge region of each cell is assigned a divided frequency band so as not to overlap with the divided frequency band used in the cell edge region in the adjacent cell.
- transmission power control is performed on the user equipment located in the cell edge region so as to increase the transmission power as compared with the user equipment located in a region other than the cell edge region.
- the user equipment located in the cell edge area Avoidance is possible. Since it is possible to avoid inter-cell interference, it is possible to improve the throughput of the user equipment located in the cell edge region.
- a certain metric Mu, f (i) is calculated for each subframe, for each user, and for each resource block, and these are compared with each other.
- i represents a temporal element (for example, subframe)
- u represents a user (user number (index))
- f represents a resource block (frequency).
- a metric is an index indicating the priority of resource block allocation to a user apparatus. The metric is used for scheduling in the base station apparatus.
- a resource block is preferentially assigned to a user apparatus that exhibits a larger metric value.
- the transmission format (data modulation scheme and channel coding rate (or data modulation scheme and data size)) in the allocated resource block is determined based on the channel state.
- an amount representing a channel state for example, SINR (Signal-to-Interference plus Noise power Ratio)
- SINR Signal-to-Interference plus Noise power Ratio
- different metrics are used. For example, from the viewpoint of increasing the system throughput, the maximum CI method is used, and the metric M u, f (i) is given by the following equation.
- E means taking an average.
- E is an average data rate, and is obtained as an average of time of about 100 ms to 1 s. The average in this case means that the influence of shadowing and distance fluctuation remains, but the influence of instantaneous fading is smoothed.
- f (i) is the same as the maximum CI method, except that an average value of reception quality for the user device is taken into account.
- a resource allocation opportunity is given when the channel condition of each user equipment is better than the average channel condition for the individual user equipment. Therefore, throughput can be improved to some extent while correcting unfairness due to the maximum CI method.
- 3GPP TR 25.814 (V7.1.0), "Physical Layer Aspects for Evolved UTRA," October 2006 3GPP R1-070103, Downlink L1 / L2 Control Signaling Channel Structure: Coding 3GPP TS 36.211 (V8.5.0), “Physical Channels and Modulation", December 2008 J.Kim, et al., IEICE Trans. Commun., Vol. E89-B, No.2, 2, pp.531-538, Feb. 2006.
- the frequency band cannot be used efficiently.
- 1/3 of the system band is allocated to the user equipment located in the cell edge region. Therefore, even when the number of user devices located in the cell edge region is larger than the number of user devices located in the region other than the cell edge, Only 1/3 of the frequency band can be allocated. In other words, since the frequency band that can be allocated to the user equipment located in the cell edge region is fixed, the entire frequency band cannot be used efficiently.
- the frequency assignment selection width is 1/3, and for user equipment located in areas other than the cell edge area, the frequency assignment selection width is 2/3. This is to be 3.
- An object of the present invention is to promote allocation of optimal frequency resources while suppressing interference with other cells in a mobile communication system.
- an aspect of the present invention is a base station apparatus in a mobile communication system that receives an uplink signal from a user apparatus, receives channel state information for each of one or a plurality of frequency resource blocks, and An acquisition unit that acquires an average value of channel state information, and a reference metric that indicates the priority of allocation of frequency resource blocks to user equipment from the channel state information acquired by the acquisition unit and the average value of the channel state information
- a reference metric calculation unit that corrects the reference metric calculated by the reference metric calculation unit by using the first parameter, and prepares a corrected metric, and a correction metric for each frequency resource block prepared by the correction unit
- a transmission unit that transmits a downlink signal in accordance with a radio resource allocation plan by a network controller, and the correction unit has a predetermined first frequency when the user apparatus belongs to a certain group distinguished by path loss.
- the present invention relates to a base station apparatus that corrects the reference metric that indicates the priority
- Another aspect of the present invention is a method in a base station apparatus of a mobile communication system, in which an uplink signal is received from a user apparatus, and channel state information and channel state information for each frequency resource block are received.
- the first parameter is used to modify the reference metric calculated by the reference metric calculation step, to prepare a modified metric, and to compare the modified metric of each frequency resource block prepared by the modification step, Schedule a resource allocation plan And a transmission step for transmitting a downlink signal according to a radio resource allocation plan in the scheduling step.
- the correction step if the user apparatus belongs to a certain group distinguished by path loss, A first parameter that takes a first value for a first frequency resource block and a second value that takes a second value for a predetermined second frequency resource block.
- the disclosed base station apparatus and method it is possible to suppress the other cell interference in the mobile communication system and to promote the optimal frequency resource allocation.
- FIG. 1 is a diagram for explaining fractional frequency reuse.
- FIG. 2 is a functional block diagram of a base station apparatus according to an embodiment of the present invention.
- FIG. 3 is a diagram illustrating an example of frequency band allocation in a base station apparatus according to an embodiment of the present invention.
- FIG. 4 is a flowchart showing an operation example according to an embodiment of the present invention.
- FIG. 5 is a diagram illustrating an example of a modified metric according to an embodiment of the present invention.
- FIG. 6 is a flowchart showing another operation example according to one embodiment of the present invention.
- FIG. 7 is a diagram illustrating a setting example of coefficient values according to an embodiment of the present invention.
- FIG. 8 is a diagram illustrating a setting example of coefficients for promoting the use of different frequencies for each path loss group according to an embodiment of the present invention.
- FIG. 2 shows a base station apparatus according to the present embodiment.
- the base station apparatus 100 is used in a mobile communication system that applies an orthogonal frequency division multiple access (OFDMA) scheme to the downlink.
- OFDMA orthogonal frequency division multiple access
- the present invention may be used not only in the OFDMA system but also in any system in which scheduling is optimized so as to suppress interference from other cells.
- this embodiment is particularly advantageous for a system that is assumed to be particularly susceptible to interference from other cells at the cell edge.
- the base station apparatus 100 includes a fast Fourier transform unit (FFT) 12, a CQI receiving unit 14, a resource allocation unit 16, and a physical downlink control channel (PDCCH) generation unit 18.
- the resource allocation unit 16 includes an FFR enhancement coefficient multiplication unit (B) 24 and a scheduler 26.
- the CQI reception unit 14 includes a reference metric calculation unit 142.
- the uplink signal includes downlink channel state (CQI: Channel Quality Indicator) information and an average value of the channel state.
- CQI Channel Quality Indicator
- the fast Fourier transform unit (FFT) 12 performs fast Fourier transform on the baseband received signal and converts the received signal into a frequency domain signal. Since the SC-FDMA scheme is used in the uplink, the signal mapped to each frequency (resource block or resource unit) can be appropriately extracted by converting the uplink received signal to the frequency domain. .
- the fast Fourier transform unit (FFT) 12 inputs a frequency domain signal to the CQI receiving unit 14.
- the CQI receiving unit 14 acquires channel state (CQI) information from the frequency domain signal input by the fast Fourier transform unit 12. In addition, the CQI receiving unit 14 acquires an average value of CQI.
- CQI channel state
- the user equipment obtains the channel state in the downlink and reports the channel state as CQI information.
- the minimum period for which CQI information is required is 2 ms.
- the user apparatus calculates an average value of the CQI from the CQI information.
- the time for calculating the average value may be 10 ms to 1 s.
- a user apparatus reports the average value of CQI with CQI information.
- the user apparatus may report CQI information periodically or periodically. The period may be different for each user device.
- the user apparatus may transmit the CQI information through a physical uplink control channel (PUCCH: Physical Uplink Control Channel), or may transmit it through a physical uplink shared channel (PUSCH: Physical Uplink Shared Channel).
- PUCCH Physical Uplink Control Channel
- PUSCH Physical Uplink Shared Channel
- the reference metric calculation unit 142 calculates the reference metric P u, f (i) using the CQI reported by the user apparatus and the average value of the CQI.
- the reference metric is expressed by equation (1).
- Equation (1) u represents a user equipment number (index), f represents a frequency block number, and i represents time or a subframe.
- CQI can be used as ⁇ u, f , and an average value of CQI can be used as E ( ⁇ u, f ).
- CQI may be converted to ⁇ u, f , or an average value of CQI may be converted to E ( ⁇ u, f ). Any conversion formula may be used for the conversion.
- the proportional fairness (PF) method is used for scheduling, but other methods may be used.
- PF proportional fairness
- the resource allocation unit 16 corrects (corrects) the reference metric P u, f (i) from the CQI receiving unit 14 with the coefficient B u, f (i), and based on the corrected metric M u, f (i). Scheduling.
- the coefficient B u, f (i) will be described later. In the following description, for the sake of convenience, the case where the coefficient B u, f (i) is multiplied as shown in Equation (2) will be described, but the modified metric may be expressed in another format as will be described later. Good.
- the resource allocation unit 16 outputs control information indicating a radio resource allocation plan.
- the base station apparatus 100 transmits a downlink signal according to the control information. Note that the process of deriving the reference metric P u, f (i) from the CQI measurement value ⁇ u, f may be performed by the resource allocation unit 16 or may be performed by another means.
- the physical downlink control channel (PDCCH) generation unit 18 receives control information indicating a radio resource allocation plan from the resource allocation unit 16 and prepares a downlink control channel.
- PDCCH physical downlink control channel
- the downlink control channel for example, PDCCH (physical downlink control channel) can be used in LTE.
- the FFR enhancement coefficient multiplier (B) 24 prepares one coefficient B u, f (i) for correcting the reference metric.
- the FFR enhancement coefficient B u, f (i) may be expressed as in Expression (3).
- u represents a user equipment
- f represents a resource block
- i represents time or a subframe.
- PL u represents a path loss or propagation loss for the user apparatus u, and indicates the influence of distance attenuation, shadowing, or the like.
- PL refB is some fixed value related to path loss, and is prepared as a system parameter. In general, the path loss increases as the distance from the base station increases, so PL u is an indicator of how far the user apparatus u is from the base station.
- the predetermined case is a case where the resource block is a predetermined resource block.
- the FFR enhancement coefficient B u, f is proportional to the coefficient b u, f .
- the FFR emphasis coefficient B u, f is obtained by appropriately standardizing the coefficient b u, f .
- the property of the FFR enhancement coefficient B u, f is substantially equal to the property of the coefficient b u, f .
- the coefficient b u, f takes a value different from 1 in a predetermined case, and takes a value of 1 in other cases.
- the predetermined case for the coefficients b u, f is a case where the resource block is a predetermined resource block, and does not depend on the state of subframes or scheduling.
- the predetermined resource block is f B
- the user block at the cell edge is prompted to allocate the resource block f B
- the resource block other than f B is likely to be used for the user apparatus not at the cell edge.
- Such resource block allocation is performed in each cell.
- the resource block that promotes use at the cell edge has a frequency different between adjacent cells (the base stations may communicate with each other in advance so that the resource block can be realized, or the system determines from the beginning. May be.)
- the FFR enhancement coefficient B u, f is the same as that in the equation (3). Even if the coefficient b u, f is expressed as in equation (4), the FFR enhancement coefficient B u, f is proportional to the coefficient b u, f . In other words, the FFR emphasis coefficient B u, f is obtained by appropriately standardizing the coefficient b u, f .
- the property of the FFR enhancement coefficient B u, f is substantially equal to the property of the coefficient b u, f .
- the coefficient b u, f takes a value different from 1 in a predetermined case, and takes a value of 1 in other cases.
- the predetermined case for the coefficients b u, f is a case where the resource block is a predetermined resource block, and does not depend on the state of subframes or scheduling. For example, if the predetermined resource block is f B , the user block at the cell edge is prompted to allocate the resource block f B, and the resource block other than f B is likely to be used for the user apparatus not at the cell edge.
- Equation (4) differs from Equation (3) in that Equation (3) uses the value obtained by dividing PL u by PL refB , while Equation (4) subtracts PL u by PL refB . A value obtained by raising the value to the power of ⁇ is used. By multiplying the value obtained by subtracting PL u by PL refB to the ⁇ power, it is possible to prompt the user at the cell edge to assign the resource block f B or to suppress the prompt.
- FIG. 3 shows an example of frequency band allocation in the base station apparatus 100 according to an embodiment of the present invention.
- the horizontal axis represents frequency
- the vertical axis represents transmission power.
- FIG. 3 shows a case where 3 cell repetition is applied to a user located at a cell edge, but it may be 2 cell repetition or 4 or more cell repetitions.
- the difference from the frequency band allocation in the FFR shown in FIG. 1 is that the frequency band that can be allocated to the user equipment located in the cell edge region is not strictly fixed. Therefore, a frequency band other than the frequency band preferentially allocated to the cell edge user apparatus may be assigned to the cell edge user apparatus.
- ⁇ is used as a parameter representing a weight when assigning a predetermined resource block f B to the user apparatus.
- the ⁇ is preferably 1 or more.
- ⁇ may be less than 1. In practice, ⁇ may be determined by simulation.
- the path loss difference (PL u -PL refB ) when the path loss difference (PL u -PL refB ) is large, it is assumed that there will be a problem that resource block allocation becomes unfair between the user equipment at the cell edge and the user equipment at the cell edge. Therefore, the value of ⁇ is reduced. Further, when the path loss difference (PL u ⁇ PL refB ) is small, it is necessary to promote the allocation of resource blocks to the user equipment at the cell edge, so the value of ⁇ is increased. By adjusting the value of ⁇ based on the path loss difference, it is possible to adjust so that resource block allocation is not unfair between the user equipment at the cell edge and the user equipment at the cell edge. For example, a threshold value may be provided for the path loss difference to adjust the value of ⁇ .
- Resource blocks are allocated in each cell. However, it is assumed that the resource block that promotes use at the cell edge has a different frequency between adjacent cells (in order to realize that the resource block that promotes use at the cell edge has a different frequency between adjacent cells)
- the stations may communicate with each other, or the system may decide from the beginning.) By promoting the use of a specific frequency for the user equipment at the cell edge, the influence of interference from other cells can be minimized.
- the reference metric is modified as necessary with the coefficient B u, f (i).
- the resource allocation plan is determined by comparing the magnitudes of the modified metrics. A specific method of resource allocation will be described later with reference to FIG.
- FIG. 4 is a flowchart for explaining an example of scheduling operation.
- the base station apparatus 100 receives an uplink signal (step S402).
- the uplink signal includes a CQI measurement value and an average value of the CQI.
- the CQI receiving unit 14 acquires CQI information and an average value of CQI.
- the CQI receiving unit 14 acquires a CQI for each user or for each resource block. In addition, the CQI receiving unit 14 also acquires an average value of CQI.
- the base station apparatus 100 calculates a reference metric (step S404).
- the reference metric calculation unit 142 calculates the reference metric P u, f (i) based on the CQI and the average value of CQI.
- the reference metric calculation unit 142 may perform further averaging using a plurality of CQI average values reported by the user apparatus.
- the reference metric P u, f (i) is expressed by Equation (5) from the viewpoint of performing scheduling by the proportional fairness method.
- P u, f (i) ⁇ u, f (i) / E ( ⁇ u, f ) (5)
- P u, f (i), ⁇ u, f (i), E ( ⁇ u, f ) may be calculated from the average value of CQI and CQI as necessary. Further, CQI may be used as ⁇ u, f (i), and an average value of CQI may be used as E ( ⁇ u, f ).
- the base station apparatus 100 corrects the reference metric calculated in step S404 based on a predetermined coefficient Bu, f , and calculates a corrected metric (step S406).
- the modified metric is expressed by equation (6).
- the FFR enhancement coefficient multiplier (B) 24 multiplies the reference metric by the FFR enhancement coefficient Bu , f .
- Base station apparatus 100 determines a radio resource allocation plan.
- the scheduler 26 allocates resource blocks to the user apparatus based on the modified metric input by the FFR enhancement coefficient unit (B) 24. From the viewpoint of allocating resource blocks to user devices that provide a larger modified metric, it is preferable to consider all possible combinations (allocation patterns) of user devices and resource blocks that are desired to be allocated.
- allocation patterns When OFDMA is used for the downlink, when a plurality of resource blocks are allocated to the user apparatus, resource blocks separated in the frequency direction can be allocated. For each of the allocation patterns, the sum of the modified metrics is calculated, and the allocation pattern that yields the largest sum is adopted as the actual allocation pattern.
- the sum of corrected metrics is derived for all possible allocation patterns.
- the allocation pattern that gives the largest value is determined as the actual allocation pattern.
- FIG. 6 is a flowchart for explaining another operation example of scheduling.
- Steps S602 to S606 are the same as steps S402 to S406 described with reference to FIG.
- step S608 the modified metrics are arranged in descending order, and a series of modified metric series ⁇ M u, f ⁇ is prepared.
- step S610 the user apparatus u and the resource block f corresponding to the maximum corrected metric max ( ⁇ M u, f ⁇ ) are specified. Then, the resource block f is assigned to the user apparatus u.
- OFDMA orthogonal frequency division multiple access
- resource blocks separated in the frequency direction can be allocated.
- step S612 the resource block f is excluded from scheduling targets.
- the modified metrics of all user devices related to the allocated resource block f are excluded from the modified metric series.
- step S614 it is determined whether or not all resource blocks have been assigned to some user device. If unassigned resource blocks remain, the flow proceeds to step S610. If no unallocated resource block remains, the flow ends.
- the modified metric sequence includes only six modified metrics for RB1 and RB3.
- the largest correction metric is found among these six correction metrics. For the current example, it is 9, which corresponds to UE3 and RB3. Therefore RB3 is assigned to UE3. Then, all the modified metrics related to RB3 are excluded from the modified metric series. In the figure, modified metrics 4, 7, and 9 of UE1, UE2, and UE3 related to RB3 are excluded. As a result, the modified metric sequence includes only three modified metrics for RB1.
- the largest of the three modified metrics is found. For the current example, it is 7, which corresponds to UE3 and RB1. Therefore, RB1 is assigned to UE3. In this way, three resource blocks are easily allocated to one or more users.
- Modified Metric is expressed by a mathematical formula obtained by multiplying the reference metric by a coefficient.
- the present invention is not limited to such a mathematical expression, and any appropriate mathematical expression may be used. This is because it is sufficient that the reference metric can be corrected for a specific frequency of a specific user.
- the modified metric may include the above coefficients as a power or power.
- B u, f is greater than 1 in the predetermined case
- B u, f is 1 in the other case
- ⁇ is greater than 1 in the predetermined case, and 1 otherwise. Therefore, the reference metric is emphasized by a power ⁇ that is larger than 1 in a predetermined case, and remains the first power unless it is a predetermined case.
- the ⁇ is different from ⁇ in the above-described embodiment.
- coefficient value The above-described coefficient B u, f (i) has been determined to be a value that can be taken from the viewpoint of correction so as to increase the reference metric in a predetermined case. A larger modified metric prompts the user to use the resource block. However, conversely, it may be possible to modify the reference metric so that a certain user does not use a certain resource block. This is because interference with other cells should be relatively reduced in the long term. From such a viewpoint, values as shown in FIG. 7 may be used for the coefficients of users other than the cell edges. In the case of FIG.
- the coefficient values are small in the resource blocks 2 and 3. Even in this case, the cell edge user can be encouraged to use the resource blocks 2 and 3 as a result. 3. Grouping The path loss value can be used to group users according to their distance from the base station as well as whether the user equipment is located at the cell edge. In this case, user devices belonging to the first group are encouraged to use the first frequency, user devices belonging to the second group are encouraged to use the second frequency, and so on. You can also.
- FIG. 8 shows a state in which coefficient values are set to encourage the use of different frequencies for each path loss group.
- the first frequency f 1 and the second frequency f 2, etc. correspond to one or more resource blocks.
- the coefficient is set so as to encourage the use of a different frequency from the group of user equipment at the cell edge of the adjacent cell.
- the frequency that can be used for each group is fixed, but in the example shown in FIG. 8, the frequency is not fixed, and a specific frequency can be used by a coefficient for correcting the reference metric. It is only recommended. This method is significantly different from the conventional method in which the frequency is fixed in that the entire system band can be used according to the value taken by the correction metric. 4).
- the reference metric was modified with one factor to derive a modified metric.
- the present invention is not limited to one coefficient, and the reference metric may be further modified from other suitable viewpoints.
- C u, f (i) is an enhancement coefficient from some other viewpoint. For example, when the average value E ( ⁇ f ) of CQI exceeds a predetermined value, a resource block can be easily allocated to the user apparatus by setting Cu, f (i) to a value larger than 1. May be.
- the downlink has been mainly described, but the present invention may be applied to the uplink.
- the base station apparatus measures the uplink reception quality for each user apparatus. For example, the uplink reception quality is measured based on the reference signal transmitted by the user apparatus. Then, the base station apparatus calculates the above-described reference metric using the uplink reception quality.
- a base station apparatus in a mobile communication system is realized.
- the base station apparatus receives an uplink signal from a user apparatus, acquires a channel state information and an average value of the channel state information for each of one or a plurality of frequency resource blocks, and is acquired by the acquisition unit
- a reference metric calculation unit for calculating a reference metric indicating a priority of allocation of frequency resource blocks to the user equipment from the channel state information and an average value of the channel state information, and a first parameter, which is calculated by the reference metric calculation unit.
- a correction unit that corrects the generated reference metric and prepares a correction metric, a scheduler that compares the correction metric of each frequency resource block prepared by the correction unit and makes a radio resource allocation plan, and a radio resource by the scheduler Transmission to transmit downlink signals according to And a part.
- the correction unit takes a first value for a predetermined first frequency resource block and a second value for a predetermined second frequency resource block when the user apparatus belongs to a certain group distinguished by path loss.
- the reference metric is modified with the first parameter taken.
- the frequency resource block that is preferentially allocated to the user located at the cell edge can be modified so as to take a larger value as the user at the cell edge.
- CQI CQI
- the first parameter B u, f (i) is calculated by the above equation (3)
- b u, f is calculated by the equation (4).
- u represents a user
- f represents a resource block
- i represents time
- F represents the number of resource blocks included in the system band
- PL u represents the path loss of the user apparatus.
- PL refB represents a predetermined reference value for path loss
- ⁇ represents a parameter indicating a weight when a predetermined resource block f B is allocated to the user apparatus.
- the predetermined case is a case where the frequency resource block is a predetermined first frequency resource block.
- Equation (3) and Equation (4) By setting the first parameter as shown in Equation (3) and Equation (4), adjustment is made so that resource block allocation is not unfair between user equipment at the cell edge and user equipment at the cell edge. it can. Since the frequency band that can be allocated to the user equipment located in the cell edge region is not strictly fixed, the entire frequency band can be used efficiently. Further, the selection range of the frequency assignment is not narrowed.
- the correction unit adjusts the value of ⁇ based on a path loss of a user apparatus and a path loss difference between predetermined reference values regarding the path loss.
- the correction unit decreases the value of ⁇ when the path loss difference is greater than or equal to a predetermined threshold, and sets the value of ⁇ when the path loss difference is less than the predetermined threshold. Enlarge.
- the correction unit calculates a correction metric by multiplying the reference metric by the first parameter.
- the frequency resource block preferentially allocated to the user located at the cell edge can be modified so as to take a larger value as the user at the cell edge.
- the scheduler makes a radio resource allocation plan according to the proportional fairness method.
- the method receives an uplink signal from a user apparatus, acquires channel state information and an average value of the channel state information for each of one or a plurality of frequency resource blocks, and the acquisition step acquired by the acquisition step A reference metric calculation step of calculating a reference metric indicating the priority of allocation of resource blocks to the user equipment from the channel state information and an average value of the channel state information; and a reference calculated by the reference metric calculation step using a first parameter A correction step for correcting a metric and preparing a correction metric, a scheduling step for making a radio resource allocation plan by comparing the correction metric of each frequency resource block prepared by the correction step, and a radio resource by the scheduling step According the allocation plan, and a transmission step of transmitting a downlink signal.
- the correcting step when the user apparatus belongs to a certain group distinguished by path loss, the first value is taken for a predetermined first frequency resource block, and the second value is taken for a predetermined second frequency resource block.
- the reference metric is modified with the first parameter taken.
- the frequency resource block that is preferentially allocated to the user located at the cell edge can be modified so as to take a larger value as the user at the cell edge.
- an apparatus for convenience of explanation, an apparatus according to an embodiment of the present invention has been described using a functional block diagram. However, such an apparatus may be realized by hardware, software, or a combination thereof.
- FFT Fast Fourier Transform
- CQI Channel Quality Indicator
- RPDCH Physical downlink control channel
- FFR enhancement coefficient multiplication unit B
- Scheduler 100 Base station device 142 Reference metric calculation unit
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Abstract
Description
右辺は、ユーザ装置uに関するサブフレームiにおける瞬時的な受信SINRを示す。説明の便宜上、上りリンクのスケジューリングが仮定されている。チャネル状態のよいユーザ装置が常に通信を行うので、スループットは最大になる。しかしながらユーザ間の公平性に欠ける。そこで、プロポーショナルフェアネス(PF: Proportional Fairness)法と呼ばれるスケジューリング法もある。PF法では、次式のメトリックが使用される。
ここで、Eは平均をとることを意味する。例えば、Eは平均のデータレートであり、100ms~1s程度の時間の平均で求められる。この場合における平均は、シャドウイングや距離変動の影響は残るが、瞬時フェージングの影響は平滑化されることを意味する。
図2は本実施例に従った基地局装置を示す。
式(1)で、uはユーザ装置の番号(インデックス)を表し、fは周波数ブロック番号を表し、iは時間又はサブフレームを表す。また、γu,fとしてCQIを用いることができ、E(γu,f)としてCQIの平均値を用いることができる。また、CQIを変換してγu,fとしてもよいし、CQIの平均値を変換してE(γu,f)としてもよい。該変換には、何らかの変換式が用いられてもよい。本実施例では、スケジューリングにプロポーショナルフェアネス(PF)法が使用されるが、他の方法が使用されてもよい。基準メトリックはスケジューリング法に依存して様々に用意されてもよい。例えば、最大CI法が使用される場合、基準メトリックは、Pu,f(i)=γu,fのように用意されてよい。
リソース割当部16は、無線リソースの割当計画を示す制御情報を出力する。基地局装置100は、該制御情報に従って下りリンクの信号を送信する。なお、CQI測定値γu,fから基準メトリックPu,f(i)を導出する処理は、リソース割当部16で行われてもよいし、更に別の手段で行われてもよい。
FFR強調係数乗算部(B)24は、基準メトリックを修正する係数の1つBu,f(i)を用意する。FFR強調係数Bu,f(i)は、一例として、式(3)のように表現されてよい。
また、係数bu,fは、式(4)のように表されてもよい。
図4はスケジューリングの動作例を説明するためのフローチャートである。
基準メトリックPu,f(i)を計算するに当たり、必要に応じて、CQI及びCQIの平均値からγu,f(i)、E(γu,f)を算出するようにしてもよい。また、γu,f(i)としてCQIを用い、E(γu,f)としてCQIの平均値を用いてもよい。
基地局装置100は、無線リソースの割当計画を決定する。スケジューラ26は、FFR強調係数部(B)24により入力された修正メトリックに基づいて、ユーザ装置に対してリソースブロックを割当てる。より大きな修正メトリックをもたらすユーザ装置にリソースブロックを割り当てる観点からは、割当を希望するユーザ装置とリソースブロックの可能な全ての組み合わせ(割当パターン)を考慮することが好ましい。下りリンクにOFDMAが使用されている場合、ユーザ装置に複数のリソースブロックを割り当てる際、周波数方向に離間したリソースブロックを割当てることができる。各割当パターンの各々について、修正メトリックの総和が計算され、最も大きな総和をもたらす割当パターンが、実際の割当パターンとして採用される。
Mu,f(i)=Bu,f(i)×Pu,f(i)
ステップS608では、修正メトリックが大きい順に並べられ、一連の修正メトリック系列{Mu,f}が用意される。
1.修正メトリック
上記の例では修正メトリックは、基準メトリックに係数が乗算された数式で表現されていた。
しかしながら、本発明はこのような数式表現に限定されず適切な如何なる数式が使用されてもよい。特定のユーザの特定の周波数について基準メトリックを修正できればよいからである。例えば、修正メトリックは、上記の係数を累乗又はべき乗として含んでもよい。
α=Bu,f(i)
上述したように、所定の場合にはBu,fは1より大きくなり、所定の場合でなければBu,fは1である。所定の場合にはαは1より大きくなり、所定の場合でなければ1である。従って所定の場合に基準メトリックは1より大きな累乗数αで強調され、所定の場合でなければ1乗のままである。該αは、上述した実施例のαとは異なる。一方、基準メトリックPu,fは、一般的なプロポーショナルフェアネス法では、Pu,f(i)=γu,f(i)/E(γu,f) として算出される。CQIの瞬時値がCQIの平均値を上回る場合、基準メトリックは1より大きくなり、CQIの瞬時値がCQIの平均値を上回らなければ1より小さくなる。従って、セル端のユーザについて、リソースが所定のリソースであった場合、1より大きな基準メトリックは1乗より急激に増えるように強調される。1より小さな基準メトリックは1乗より急激に減るように強調される。その結果、所定の場合にそのユーザに所定のリソースを割り当てるべきことが、より色濃く修正メトリックに反映される。
2.係数の値
上記の係数Bu,f(i)は、所定の場合に基準メトリックを大きくするように修正する観点からとり得る値が決定されていた。より大きな修正メトリックは、そのユーザにそのリソースブロックを使用させることを促す。しかしながら、逆に、あるユーザにあるリソースブロックを使用させないように基準メトリックを修正することも考えられる。長期的に見て他セル干渉が相対的に減っていればよいからである。このような観点からは、セル端以外のユーザの係数について、図7に示されるような値が使用されてもよい。図7の場合、リソースブロック2,3で係数の値が小さくなっている。このようにしても、結果的にセル端ユーザがリソースブロック2,3を使用するのを促すことができる。
3.グループ化
パスロスの値は、ユーザ装置がセル端に位置するか否かだけでなく、ユーザを基地局からの距離に応じてグループ分けするのにも使用できる。この場合において、第1グループに属するユーザ装置には第1周波数の利用を促し、第2グループのユーザ装置には第2周波数の利用を促し、以下同様にグループ毎に異なる周波数の利用を促すこともできる。
4.別の係数
上記の説明では、基準メトリックは1つの係数で修正され、修正メトリックが導出されていた。しかしながら本発明は1つの係数に限定されず、適切な他の観点から基準メトリックが更に修正されてもよい。例えば、修正メトリックは、
Mu,f(i)=Bu,f(i)×Cu,f(i)×Pu,f(i)
のようにして導出されてもよい。Cu,f(i)は、何らかの別の観点による強調係数である。例えば、CQIの平均値E(γf)が所定値を超えていた場合、Cu,f(i)が1より大きな値をとるようにすることで、そのユーザ装置にリソースブロックが割り当てられやすくしてもよい。
14 CQI(Channel Quality Indicator)受信部
16 リソース割当部
18 物理下りリンク制御チャネル(PDCCH)生成部
24 FFR強調係数乗算部(B)
26 スケジューラ
100 基地局装置
142 基準メトリック計算部
Claims (6)
- 移動通信システムにおける基地局装置であって、
ユーザ装置から上りリンクの信号を受信し、1又は複数の周波数リソースブロック毎にチャネル状態情報及び該チャネル状態情報の平均値を取得する取得部と、
該取得部により取得された前記チャネル状態情報及び該チャネル状態情報の平均値からユーザ装置に対する周波数リソースブロックの割当ての優先度を示す基準メトリックを計算する基準メトリック計算部と、
第1パラメータで、前記基準メトリック計算部により計算された基準メトリックを修正し、修正メトリックを用意する修正部と、
該修正部により用意された各周波数リソースブロックの修正メトリックを比較し、無線リソースの割当計画を立てるスケジューラと、
該スケジューラによる無線リソースの割当計画に従って、下りリンクの信号を送信する送信部と
を有し、
前記修正部は、ユーザ装置がパスロスで区別される或るグループに属する場合、所定の第1の周波数リソースブロックについて第1の値をとり、所定の第2の周波数リソースブロックについて第2の値をとる第1パラメータで、前記基準メトリックを修正する基地局装置。 - 請求項2記載の基地局装置において、
前記修正部は、ユーザ装置のパスロスとパスロスに関する所定の基準値とのパスロス差に基づいて、前記αの値を調節する基地局装置。 - 請求項3に記載の基地局装置において、
前記修正部は、前記パスロス差が所定の閾値以上である場合にはαの値を小さくし、前記パスロス差が前記所定の閾値未満である場合にはαの値を大きくする基地局装置。 - 請求項1に記載の基地局装置において、
前記スケジューラは、プロポーショナルフェアネス法に従って無線リソースの割当計画を立てる基地局装置。 - 移動通信システムの基地局装置における方法であって、
ユーザ装置から上りリンクの信号を受信し、1又は複数の周波数リソースブロック毎にチャネル状態情報及び該チャネル状態情報の平均値を取得する取得ステップと、
該取得ステップにより取得された前記チャネル状態情報及び該チャネル状態情報の平均値からユーザ装置に対するリソースブロックの割当ての優先度を示す基準メトリックを計算する基準メトリック計算ステップと、
第1パラメータで、前記基準メトリック計算ステップにより計算された基準メトリックを修正し、修正メトリックを用意する修正ステップと、
前記修正ステップにより用意された各周波数リソースブロックの修正メトリックを比較し、無線リソースの割当計画を立てるスケジューリングステップと、
該スケジューリングステップによる無線リソースの割当計画に従って、下りリンクの信号を送信する送信ステップと
を有し、
前記修正ステップでは、ユーザ装置がパスロスで区別される或るグループに属する場合、所定の第1の周波数リソースブロックについて第1の値をとり、所定の第2の周波数リソースブロックについて第2の値をとる第1パラメータで、前記基準メトリックを修正する方法。
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JP2007288676A (ja) * | 2006-04-19 | 2007-11-01 | Ntt Docomo Inc | 無線基地局および送信制御方法 |
JP2007336392A (ja) * | 2006-06-16 | 2007-12-27 | Ntt Docomo Inc | 移動局装置および基地局装置並びに下りリソース割り当て方法 |
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US20130215784A1 (en) * | 2010-11-10 | 2013-08-22 | Telefonaktiebolaget L M Ericsson (Publ) | Radio Base Station and a Method Therein |
EP2638762A4 (en) * | 2010-11-10 | 2015-10-21 | Ericsson Telefon Ab L M | RADIO BASE STATION AND METHOD THEREFOR |
US9445424B2 (en) * | 2010-11-10 | 2016-09-13 | Telefonaktiebolaget Lm Ericsson (Publ) | Radio base station and method for scheduling radio resources for user equipment |
WO2012114704A1 (en) * | 2011-02-23 | 2012-08-30 | Nec Corporation | Radio resource range setting device, radio resource range setting method, and recording medium |
CN103404218A (zh) * | 2011-02-23 | 2013-11-20 | 日本电气株式会社 | 无线电资源范围设定设备、无线电资源范围设定方法和记录介质 |
WO2012120797A1 (en) * | 2011-03-04 | 2012-09-13 | Nec Corporation | Base station, radio resource allocation method, and recording medium |
Also Published As
Publication number | Publication date |
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US8711670B2 (en) | 2014-04-29 |
JP5059798B2 (ja) | 2012-10-31 |
US20120008489A1 (en) | 2012-01-12 |
JP2010206476A (ja) | 2010-09-16 |
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