KR101494684B1 - Scheduling method of uplink of ofdma system - Google Patents

Abstract

An uplink scheduling method of a base station according to an embodiment of the present invention includes the steps of: receiving a request bandwidth from a plurality of terminals; calculating an allocation bandwidth on the basis of the request bandwidth; calculating the number of slots for allocating a slot to each of the terminals by using the allocation bandwidth; determining an MCS level for each of the terminals by using the number of slots; classifying the terminal into first and second groups on the basis of the number of slots; and re-setting the number of slots and MCS levels by distinguishing the first group from the second group.

Description

Technical Field [0001] The present invention relates to a scheduling method of a base station,

An embodiment of the present invention relates to an uplink scheduling method of a base station, and more particularly, to an uplink scheduling method capable of improving sector throughput of a base station constituting an OFDMA system.

Recently, as interest in 4G mobile communication has increased in domestic and foreign countries, researches on systems satisfying the requirements of 4G mobile communication systems are actively being carried out. In particular, the Orthogonal Frequency Division Multiplexing (OFDM) scheme compensates for channel distortion with a high transmission efficiency and a simple tap equalizer, and imposes a severe inter-symbol interference (ISI) problem on the cyclic prefix Cyclic Prefix), it is attracting attention as a suitable method for 4th generation mobile communication system.

Based on the advantages of such an OFDM system, there is an increasing interest in an Orthogonal Frequency Division Multiple Access (OFDM) system which is a multi-user access scheme for satisfying various QoS (Quality of Service). An OFDMA system is a system that enables multiple access by allocating a plurality of subcarriers and symbols to a plurality of terminals. A base station allocates specific subcarriers and symbols to each terminal, and transmits a data signal through the allocated area . At this time, the base station should appropriately control the strength and the modulation and coding scheme (MCS) level of the signals transmitted from the respective terminals so that the base station receiver can normally receive signals of the respective terminals. To this end, the BS allocates radio resources to the UEs considering the transmission loss of each UE, the noise level of the Node B, the number of subcarriers to be allocated to the UE, and the MCS to be used by the UE.

However, according to the related art, it is possible to allocate the radio resources and the MCS level so that each terminal can transmit errorlessly using a combination of the number of slots and the MCS level that can be allocated to each terminal, but the overall sector throughput And a method for distributing a limited wireless bandwidth to each terminal is insufficient.

Accordingly, an object of the present invention is to provide an uplink scheduling method capable of improving sector throughput of a base station.

The problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

A method for uplink scheduling of a base station according to an embodiment of the present invention includes receiving a request bandwidth from a plurality of terminals, calculating an allocated bandwidth based on the requested bandwidth, Determining a MCS level of each of the plurality of terminals using the number of slots, calculating the MCS level of each of the plurality of terminals based on the number of slots, Grouping the first group and the second group, and resetting the slot number and the MCS level by classifying the first group and the second group.

In one embodiment, the step of calculating an allocation bandwidth based on the required bandwidth may calculate the allocated bandwidth by summing the required bandwidth and the remaining bandwidth.

In one embodiment, calculating the number of slots for allocating slots to each of the plurality of terminals using the allocated bandwidth may be performed using Equation (1).

[Equation 1]

Here, Sipre_alloc is the number of slots to be allocated to the ith terminal, BWireq is the requested bandwidth of the ith terminal, Hibase is the first headroom of the ith terminal, Ei is the slot utilization index of the ith terminal, and Savail is defined as the number of valid slots And the first headroom refers to a headroom when the i-th terminal normally communicates with the base station through one slot at the lowest MCS level.

In one embodiment, determining the MCS level of each of the plurality of terminals using the number of slots may include calculating a number of symbol frames required for signal transmission of each of the plurality of terminals based on the number of slots, Calculating a second headroom of each of the plurality of terminals using the symbol frame number, and determining the MCS level based on the second headroom.

In one embodiment, classifying the plurality of terminals into a first group and a second group based on the number of slots may include comparing the ratio of the first headroom to the number of slots to a threshold value, And classifying the plurality of terminals into the second group if the ratio is not greater than the threshold value.

In one embodiment, the step of allocating slots other than slots to be allocated to the first group and the second group to terminals other than the first group and the second group.

The uplink scheduling method of the base station according to an embodiment of the present invention can improve the sector throughput.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to more fully understand the drawings recited in the detailed description of the present invention, a detailed description of each drawing is provided.
1 is a conceptual diagram illustrating an OFDMA system including a base station according to an embodiment of the present invention.
2 is a block diagram showing the base station of FIG. 1 in more detail.
3 is a flowchart illustrating a method of uplink scheduling of a BS according to an embodiment of the present invention.
4 is a flowchart showing the step S140 of FIG. 3 in more detail.
FIG. 5 is a diagram illustrating a relation between a symbol, a symbol frame, and a slot according to an embodiment of the present invention.
FIG. 6 shows an Adaptive Modulation and Coding (AMC) table according to an embodiment of the present invention.
FIG. 7 is a flowchart showing the step S160 of FIG. 3 in more detail.
FIG. 8 is a flowchart showing the step S170 of FIG. 3 in more detail.
9 is a table storing the relationship between the optimization coefficient and the MCS level according to an embodiment of the present invention.

It is to be understood that the specific structural or functional descriptions of embodiments of the present invention disclosed herein are only for the purpose of illustrating embodiments of the inventive concept, But may be embodied in many different forms and is not limited to the embodiments set forth herein.

Embodiments in accordance with the concepts of the present invention are capable of various modifications and may take various forms, so that the embodiments are illustrated in the drawings and described in detail herein. It should be understood, however, that it is not intended to limit the embodiments according to the concepts of the present invention to the particular forms disclosed, but includes all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

The terms first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The terms are intended to distinguish one element from another, for example, without departing from the scope of the invention in accordance with the concepts of the present invention, the first element may be termed the second element, The second component may also be referred to as a first component.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between. Other expressions that describe the relationship between components, such as "between" and "between" or "neighboring to" and "directly adjacent to" should be interpreted as well.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises" or "having", etc. are intended to specify the presence of stated features, integers, steps, operations, elements, parts or combinations thereof, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the meaning of the context in the relevant art and, unless explicitly defined herein, are to be interpreted as ideal or overly formal Do not.

The present invention relates to an uplink scheduling method of an OFDMA system, and more particularly, to an uplink scheduling method capable of improving sector throughput of an OFDMA system. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily carry out the technical idea of the present invention. .

1 is a conceptual diagram illustrating an OFDMA system including a base station according to an embodiment of the present invention.

Referring to FIG. 1, the OFDMA system 100 includes a base station 110 and terminals 120. The terminals 120 are assumed to be located in the sector of the base station 110. For example, the sector may be defined as a communication range of the base station 110. [ The BS 110 and the MSs 120 may transmit and receive signals using an Orthogonal Frequency Division Multiple Access (OFDMA) scheme.

The terminals 120 may be divided into a plurality of groups and managed by the base station 110. The terminals 120 may be divided into, for example, three groups (a, b, c), but are not limited thereto.

The BS 110 calculates the number of slots and the MCS level allocated to each of the MSs 120, classifies the MSs 120 into the plurality of groups, calculates the number of slots of the MSs included in the plurality of groups, The MCS level can be reset for each of the plurality of groups. This will be described in more detail with reference to Figs. 2 to 9 below.

2 is a block diagram showing the base station of FIG. 1 in more detail.

Referring to FIG. 2, the base station 110 includes a processor 111, a memory 112, and a modem 113.

The processor 111 controls the overall operation of the base station 110. The processor 111 controls the modem 113 to receive a signal (e.g., an OFDM symbol) from the terminal 120 (see FIG. 1).

The processor 111 may perform an uplink scheduling operation on the SSs 120 of the BS 110. For this, the processor 111 may calculate the number of slots and the MCS level allocated to each of the terminals 120. [ The processor 111 classifies the terminals 120 into the plurality of groups based on the calculated number of slots and the MCS level, and sets the number of slots and the MCS level of the terminals included in the plurality of groups, You can reset it. The operation of the processor 111 will be described in more detail with reference to Figs. 3 to 9 below.

The memory 112 may be an operational memory of the processor 111 and the memory 112 may comprise a random access memory such as, for example, DRAM, SRAM, MRAM, PRAM, RRAM,

The modem 113 communicates with the plurality of terminals 120 under the control of the processor 111. The modem 113 may be implemented as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA), for example.

3 is a flowchart illustrating a method of uplink scheduling of a BS according to an embodiment of the present invention. 4 is a flowchart showing the step S140 of FIG. 3 in more detail. FIG. 5 is a diagram illustrating a relation between a symbol, a symbol frame, and a slot according to an embodiment of the present invention. FIG. 6 shows an Adaptive Modulation and Coding (AMC) table according to an embodiment of the present invention. FIG. 7 is a flowchart showing the step S160 of FIG. 3 in more detail. FIG. 8 is a flowchart showing the step S170 of FIG. 3 in more detail. 9 is a table storing the relationship between the optimization coefficient and the MCS level according to an embodiment of the present invention.

Referring to FIG. 3, a method for uplink scheduling of a base station according to an embodiment of the present invention includes receiving a required bandwidth from a plurality of terminals (S110), summing the required bandwidth and the remaining bandwidth, (S130) of calculating a slot number (first slot number) to be allocated to each of the plurality of terminals using the allocated bandwidth (S130), calculating a first MCS level (S140), classifying the plurality of terminals into first and second groups based on the first slot number (S150), determining a second slot number and a second slot number of the terminals included in the first group (S160) calculating a second MCS level, calculating a third slot number and a third MCS level of the terminals included in the second group (S170), and calculating a third MCS level of the terminals included in the first and second groups And the remaining slots allocated to To a terminal included in the third group (S180).

Hereinafter, each step will be described in detail. It should be understood that the following steps are applied to any one of the plurality of terminals 120 (see FIG. 1) for the sake of convenience of description, but it should be understood that the same applies to each of the plurality of terminals will be.

In step S110, the modem 113 (see FIG. 2) may receive the requested bandwidth BWireq from each of the plurality of terminals. Here, i is a natural number, and can be defined as a terminal number for distinguishing each terminal (for example, if i is 1, the first terminal). The requested bandwidth BWireq is included in a symbol frame transferred from each of the plurality of terminals 120 to the modem 113, for example. The received requested bandwidth will be transmitted to the processor 111 (see FIG. 2).

In step S120, the processor 111 calculates the allocated bandwidth by summing the required bandwidth BWireq and the remaining bandwidth BWires. The residual bandwidth BWires may mean a bandwidth not allocated by the base station 110 (see FIG. 1) among the bandwidth requested by the terminal over the previous frame, for example. The allocated bandwidth may be a bandwidth allocated to each of the plurality of terminals 120. [

In step S130, the processor 111 calculates the number of slots (first slot number, Sipre_alloc) allocated to each of the plurality of terminals 120 using the allocated bandwidth. Specifically, the processor 111 calculates the first slot number (Sipre_alloc) using Equation (1).

Herein, Sipre_alloc denotes the first slot number of the ith terminal, BWireq denotes the requested bandwidth of the ith terminal, Hibase denotes the first headroom of the ith terminal, Ei denotes the usage index of the ith terminal, and Savail denotes an effective slot. The first headroom may be a headroom of the terminal when the i-th terminal communicates with the base station at the lowest MCS level using one slot and normally communicates according to a Carrier to Interference Ratio (CINR) (headroom).

Change mathematical notation

The utilization index Ei is defined as an index indicating how much the radio resource (e.g., a slot) allocated by the i < th > In the present embodiment, the utilization index Ei is defined as having a default value of 1.0. The utilization index Ei is defined to increase by 0.1 in the case of transmitting using all the slots allocated to the terminal, and to decrease by 0.1 in the case of not using all slots. Further, the maximum value of the utilization index (Ei) is defined as 1.0, and the minimum value is defined as 0.5. The effective slot (Savail) is defined as the number of slots that can actually carry data among the entire slots of the frame.

In step S140, the processor 111 determines a first MCS level using the first slot number (Sipre_alloc).

Referring to FIG. 4, in operation S140, the number of symbol frames necessary for signal transmission of a mobile station is calculated based on the number of first slots in operation S141. In operation S141, (S142) of determining the first MCS level for the terminal based on the second headroom (S143). The second headroom may be a head for the case where the terminal transmits a signal to the base station 110 according to the lowest MCS level (for example, MCS level 1, see FIG. 6 below) of the calculated number of symbol frames Room.

Referring to FIG. 5, the relationship between a symbol, a symbol frame, and a slot is shown. In this embodiment, the time length of one slot is equal to one symbol, and one symbol frame is assumed to be composed of fifteen symbols, but the present invention is not limited thereto. The relation between the symbol, the symbol frame, and the slot may be predetermined according to the setting and stored in the memory 112 (see FIG. 2).

In step S 141, the processor 111 calculates the number of symbol frames necessary for signal transmission of the UE, with reference to Equation (2).

Here, Sipre_alloc is the number of first slots of the i-th UE, and ceil is defined as a rounding function. For example, if the number of the first slots is 16, the number of symbol frames will be calculated as 2.

In step S142, the processor 111 calculates a second headroom using the following equation (3).

Here, Hi is defined as the second headroom of the i-th terminal, Hibase is defined as the first headroom of the i-th terminal, and W is defined as the number of the symbol frames. The Hi and Hibase are defined in dB.

That is, each terminal has a margin transmission power corresponding to the second headroom for transmitting W symbol frames, and each terminal can use a higher MCS level by maximizing the transmission power.

In step S143, the processor 111 calculates the first MCS level using Equation (4) below. The first MCS level may mean a maximum allowable MCS level for the terminal. The first MCS level is defined as a maximum k value satisfying Equation (4) below.

Herein, CINR_MCS_k is defined as a minimum received CINR required by the BS 110 when the MS transmits a k-level MCS (see FIG. 6 below) to the BS 110, 110) can be defined as a reference value when the AMC (Adaptive Modulation and Coding) function is used. The AMC function is, for example, a function that the base station 110 automatically adjusts the MCS level of each terminal according to a channel condition.

For example, referring to FIG. 6, the CINR_MCS_1 is 3 dB. If the second headroom Hi is 7dB, the k value can be calculated to be 3. This means that the UE can transmit the MCS level (MCS level 3) of 16 QAM 1/2 to the BS 110 and can transmit a larger amount of data using the allocated number of slots.

Referring again to FIG. 3, in step S150, the processor 111 classifies the plurality of terminals into first and second groups based on the first slot number and the first MCS level. The processor 111 may reduce the number of allocated slots and increase the transmission power by grouping the groups of terminals into a first group by optimizing the MCS level to be used and the number of slots to be allocated, Can be classified into the second group.

For example, the processor 111 classifies a terminal having a ratio of the first slot number (Sipre_alloc) to the first headroom to a first group, and a part of the other terminals Can be classified into the second group. However, the criteria by which the processor 111 classifies the plurality of terminals into the first group and the second group is not limited thereto, and the plurality of terminals can be classified using various criteria.

The processor 111 may reset the number of slots and the MCS level according to different processes of the terminals included in the first group and the second group, respectively.

In step S160, the processor 111 calculates a second number of slots and a second MCS level of the UEs included in the first group. In this case, the UEs included in the first group are allocated slots according to the number of the second slots, and will communicate with the BS 110 according to the second MCS level.

Referring to FIG. 7, step S160 includes a step S161 of setting a re-determination coefficient, a step S162 of calculating the number of the second slots using the re-determination coefficient, and a step of determining the second MCS level S163). In step S161, the processor 111 sets the recrystallization coefficient N. [

For example, the recrystallization coefficient N may be a predetermined value of at least one rational number. In step S162, the processor 111 may calculate the second slot number using the following equation (5).

Here, Sialloc is the number of the second slot of the i-th UE, N is the re-determination coefficient, and Sipre_alloc is defined as the number of the first slots of the i-th UE.

In step S163, the processor 111 may determine the first MCS level or a higher MCS level as the second MCS level.

For example, if the first slot number (Sipre_alloc) is 60, the first MCS level is 16 QAM 1/2, and the UE transmits data The headroom of the terminal is assumed to be 1dB.

In this case, if the recrystallization coefficient N is set to 2, the number of slots (the number of the second slots Sialloc) set in the terminal is halved (i.e., the number of the second slots is 30) The radio resource (e.g., slot) increases and the headroom of the terminal increases from 1 dB to 4 dB.

That is, the number of slots (the number of the second slots) allocated to the terminals included in the first group is reduced by half, while the amount of data that the terminals included in the first group can transmit to the base station 110 is 2/3 The sector throughput of the base station 110 can be improved.

In step S170, the processor 111 calculates the third slot number and the third MCS level of the UEs included in the second group. Referring to FIG. 8, in operation S 170, the number of the third slots is calculated using the number of the first slots S 171, the step S 172 of determining a third MCS level corresponding to the number of the third slots, , Comparing the third MCS level with the first MCS level (S173), selecting the third slot number and the third MCS level when the third MCS level is greater than the first MCS level (S174 And selecting the first slot number and the first MCS level when the third MCS level is not greater than the first MCS level (S175).

In step S171, the processor 111 calculates the number of the third slots by dividing the number of the first slots by the optimum number Opt. This can be performed using Equation (6) below.

Here, Opt is an optimization coefficient, and Sitemp is defined as the number of third slots of the i < th > The reason why the number of the third slots (Sitemp) is calculated by dividing the first slot number Sipre_alloc by the optimization coefficient Opt is that if the MCS level of the terminal becomes high even if the number of slots allocated to the terminal decreases, This is because the amount of transmittable data can be kept constant.

The optimization coefficient Opt is as shown in FIG. The optimization coefficient Opt may be determined in advance using the first number of slots (Sipre_alloc) and the first MCS level. The optimization coefficient Opt may be stored in advance in the memory 113 (see FIG. 2). The optimization coefficient Opt may mean a rate at which a transmittable amount of data per unit slot increases when an MCS level which is one level higher than the current MCS level is used.

For example, when the UE transmits data to the Node B 110 using the MCS level of QPSK 3/4, the UE increases the transmission rate by 1.5 times as compared with the case of using the MCS level of QPSK 1/2 As shown in FIG.

In step S172, the processor 111 may determine a third MCS level corresponding to the third slot number through step S140 described above.

In step S173, the processor 111 compares the first MCS level with the third MCS level.

In step S174, the processor 111 selects the third slot number and the third MCS level when the third MCS level is greater than the first MCS level. In this case, the UEs included in the second group are allocated slots according to the number of the third slots and will communicate with the BS 110 according to the third MCS level.

In step S175, the processor 111 selects the first slot number and the first MCS level when the third MCS level is not greater than the first MCS level. In this case, the terminals included in the second group are allocated slots according to the number of the first slots and will communicate with the base station 110 according to the first MCS level.

That is, the UEs included in the second group can transmit the same amount of data to the Node B 110, and the number of slots can be allocated to the UEs included in another group, Can be improved.

In step S180, the processor 111 allocates the remaining slots allocated to the terminals included in the first and second groups to the terminals included in the third group.

Specifically, the processor 111 allocates the remaining slots allocated to the terminals included in the first group and the second group among all slots allotable by the base station 110 to terminals included in the third group will be.

Therefore, according to the above description, the uplink scheduling method of the base station according to an embodiment of the present invention can efficiently schedule the uplink radio resources of the terminals included in the sector.

Meanwhile, a method for uplink scheduling of a BS according to an embodiment of the present invention may be implemented in the form of a program command that can be performed through various computer means and recorded in a computer-readable medium.

Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magneto-optical media such as floptical media; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like.

Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. Therefore, the scope of the present invention should not be limited to the above-described embodiments, but should be determined by the equivalents of the claims of the present invention as well as the claims of the following.

100: OFDMA system
110: base station
120: terminal
111: Processor
112: memory
113: Modem

Claims (6)

Receiving a request bandwidth from a plurality of terminals;
Calculating an allocation bandwidth based on the required bandwidth;
Calculating a slot number for allocating a slot to each of the plurality of terminals using the allocated bandwidth;
Determining an MCS level of each of the plurality of terminals using the number of slots;
Classifying the plurality of terminals into a first group and a second group based on the number of slots; And
And resetting the slot number and the MCS level by classifying the first group and the second group. The method according to claim 1,
Wherein the step of calculating the allocated bandwidth based on the required bandwidth calculates the allocated bandwidth by summing the requested bandwidth and the remaining bandwidth. 3. The method of claim 2,
Wherein the step of calculating a slot number for allocating a slot to each of the plurality of UEs using the allocated bandwidth is performed using Equation (1).
[Equation 1]

Here, Sipre_alloc is the number of slots to be allocated to the ith terminal, BWireq is the requested bandwidth of the ith terminal, Hibase is the first headroom of the ith terminal, Ei is the slot utilization index of the ith terminal, and Savail is defined as the number of valid slots And the first headroom refers to a headroom when the i-th terminal normally communicates with the base station through one slot at the lowest MCS level. The method of claim 3,
Wherein determining the MCS level of each of the plurality of terminals using the number of slots comprises: calculating a number of symbol frames necessary for signal transmission of each of the plurality of terminals based on the number of slots;
Calculating a second headroom of each of the plurality of terminals using the number of symbol frames; And
And determining the MCS level based on the second headroom. The method of claim 3,
Wherein the step of classifying the plurality of terminals into the first group and the second group based on the number of slots compares a ratio of the first headroom to the number of slots to a threshold value, And classifying the plurality of terminals into the second group if the ratio is not greater than the threshold value. The method according to claim 1,
And allocating slots other than slots to be allocated to the first group and the second group to terminals other than the first group and the second group.

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