KR20170090241A - Apparatus and Method for Scheduling Component Carrier in Carrier Aggregation System - Google Patents

Abstract

A method for elementary carrier scheduling comprising the steps of: confirming the traffic load of each of the element carriers; confirming the channel condition of each of the element carriers; determining, for each of the element carriers, Calculating a load balancing metric; and comparing the calculated load balancing metric values to assign an element carrier to be mapped.

Description

[0001] Apparatus and Method for Scheduling Component Carrier in Carrier Aggregation System [

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication, and more particularly, to an apparatus and method for carrier scheduling in a mobile communication system supporting carrier wave aggregation.

A multiple component carrier system refers to a wireless communication system capable of supporting carrier aggregation. Carrier aggregation is a technique for efficiently using a fragmented small band, in which one base station bundles a plurality of physically continuous or non-continuous bands in the frequency domain to use a logically large band So as to achieve the same effect as the above. Multi-element carrier systems support multiple component carriers (CCs) that are distinct in the frequency domain. The element carrier includes an uplink element carrier used in the uplink and a downlink element carrier used in the downlink. A DL serving as a serving cell may be formed by combining a downlink component carrier and an uplink component carrier. Or one serving cell may be composed of only the downlink component carrier.

In such a multiple component carrier system, there are two methods in which a base station allocates an element carrier to a terminal supporting carrier aggregation.

First, the base station requests the signal strength of the candidate element carriers to the terminal and allocates the element carrier having the highest signal strength, that is, the elementary carrier having the best channel state. The following is a method of allocating according to the load of the candidate element carriers.

However, when the elementary carriers are allocated by comparing the signal strengths of the candidate element carriers, a situation may occur in which the load between the element carriers is unequal. When the element carriers are allocated according to the load of the element carriers, While the element carriers have similar channel characteristics, they can exhibit optimal system performance, while the channel state is not taken into consideration, so that the maximum transmission rate obtained through the allocated element carrier can be lowered.

The present invention provides an apparatus and method for element carrier scheduling in a carrier aggregation system that considers both the load imbalance and the transmission rate of element carriers in a small cell base station environment supporting carrier aggregation.

A method for elementary carrier scheduling comprising the steps of: confirming the traffic load of each of the element carriers; confirming the channel condition of each of the element carriers; determining, for each of the element carriers, Calculating a load balancing metric; and comparing the calculated load balancing metric values to assign an element carrier to be mapped.

The present invention relates to an elementary carrier scheduling apparatus, comprising: a traffic load verifying unit for verifying a traffic load of each of element carriers; a channel state verifying unit for verifying a channel state of each of the element carriers; And a component carrier allocation unit for comparing the calculated load balancing metrics with each other and allocating an element carrier having the highest value to the user terminal.

The present invention can ensure optimal performance by not allocating to the element carrier having a large load in consideration of the channel state and the amount of the load for each element carrier and at the same time allocating resources considering channel state for each element carrier.

1 shows a wireless communication system to which the present invention is applied.
FIG. 2 shows an example of a protocol structure for supporting a multi-element carrier wave to which the present invention is applied.
FIG. 3 shows an example of a frame structure for a multi-component carrier wave operation to which the present invention is applied.
4 is a flowchart illustrating an element carrier scheduling method in a carrier aggregation system according to an embodiment of the present invention.
5 is a configuration diagram of an element carrier scheduling apparatus in a carrier aggregation system according to an embodiment of the present invention.
6 is a graph showing a Jain's Fairness Index graph according to the present invention.
7 is a diagram illustrating cell total throughput according to the present invention.

1 shows a wireless communication system to which the present invention is applied.

Referring to FIG. 1, a wireless communication system 10 is widely deployed to provide various communication services such as voice, packet data, and the like. The wireless communication system 10 includes at least one base station (BS) 11 and a repeater (not shown). Each base station 11 provides communication services to specific cells (15a, 15b, 15c). The cell may again be divided into multiple regions (referred to as sectors).

A user equipment (UE) 12 may be fixed or mobile and may be a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, (personal digital assistant), a wireless modem, a handheld device, and the like. The base station 11 may be called by other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, a femto base station, a home node B, . The cell must be interpreted in a comprehensive meaning to indicate a partial area covered by the base station 11 and includes all the coverage areas such as a megacell, a macrocell, a microcell, a picocell, a femtocell, and a small cell to be.

Hereinafter, downlink refers to communication from the base station 11 to the terminal 12, and uplink refers to communication from the terminal 12 to the base station 11. In the downlink, the transmitter may be part of the base station 11, and the receiver may be part of the terminal 12. In the uplink, the transmitter may be part of the terminal 12, and the receiver may be part of the base station 11. There are no restrictions on multiple access schemes applied to wireless communication systems. (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-FDMA (SC-FDMA), OFDM- -CDMA, < / RTI > A TDD (Time Division Duplex) scheme in which uplink and downlink transmissions are transmitted using different time periods, or an FDD (Frequency Division Duplex) scheme in which they are transmitted using different frequencies can be used.

A carrier aggregation (CA) supports a plurality of carriers and is also referred to as spectrum aggregation or bandwidth aggregation. The individual unit carriers tied by carrier aggregation are called component carriers (CCs). Each element carrier is defined as the bandwidth and center frequency. Carrier aggregation is introduced to support increased throughput, prevent cost increases due to the introduction of wideband radio frequency (RF) devices, and ensure compatibility with existing systems. For example, if five elementary carriers are allocated as the granularity of a carrier unit having a bandwidth of 20 MHz, it can support a bandwidth of up to 100 MHz.

FIG. 2 shows an example of a protocol structure for supporting a multi-element carrier wave to which the present invention is applied.

Referring to FIG. 2, a common medium access control (MAC) entity 210 manages a physical layer 220 using a plurality of carriers. The MAC management message transmitted on a specific carrier may be applied to other carriers. That is, the MAC management message is a message capable of controlling other carriers including the specific carrier.

The physical layer 220 may operate as a time division duplex (TDD) and / or a frequency division duplex (FDD).

There are several physical control channels used in the physical layer 220. A Physical Downlink Control Channel (PDCCH) informs the UE of paging channel (PCH), resource allocation of downlink shared channel (DL-SCH), and hybrid automatic repeat request (HARQ) information related to DLSCH. The PDCCH may carry an uplink grant informing the UE of the resource allocation of the uplink transmission. A physical control format indicator channel (PCFICH) informs the UE of the number of OFDM symbols used for PDCCHs and is transmitted every subframe.

PHICH (Physical Hybrid ARQ Indicator Channel) carries HARQ ACK / NAK signal in response to uplink transmission.

A physical uplink control channel (PUCCH) carries uplink control information such as HARQ ACK / NAK, scheduling request and CQI for downlink transmission. A physical uplink shared channel (PUSCH) carries an uplink shared channel (ULSCH). A physical random access channel (PRACH) carries a random access preamble.

FIG. 3 shows an example of a frame structure for a multi-component carrier wave operation to which the present invention is applied.

Referring to FIG. 3, a frame includes 10 subframes. The subframe includes a plurality of OFDM symbols. Each element carrier may have its own control channel (e.g. PDCCH). The multi-element carriers may or may not be adjacent to each other. The terminal may support one or more carriers according to its capabilities.

Element carriers can be divided into Primary Component Carrier (PCC) and Secondary Component Carrier (SCC) depending on whether they are active or not. The primary carrier is always the active carrier, and the sub-carrier is the carrier that is activated / deactivated according to certain conditions. Activation means that the transmission or reception of traffic data is performed or is in a ready state. Deactivation means that transmission or reception of traffic data is impossible and measurement or transmission / reception of minimum information is possible. The terminal may use only one major carrier or use one or more sub-carrier with carrier. A terminal may be allocated a primary carrier and / or secondary carrier from a base station.

4 is a flowchart illustrating an element carrier scheduling method in a carrier aggregation system according to an embodiment of the present invention.

Referring to FIG. 4, the base station checks the traffic load of each element carrier before calculating the elementary carrier selection metric of each terminal (S410). At the same time, the base station confirms the channel state of each of the element carriers (S420).

Then, the base station calculates the value of the traffic load of each of the element carriers identified in S410 and the value of the channel state of each of the element carriers identified in S420 using all Equation (1) A Proportional Load Balancing (PLB) metric for each of the carriers is calculated (S430).

Then, the base station allocates the element carrier having the highest value among the PLB (Proportional Load Balancing) metric values for all the element carriers calculated at S430 (S440). That is, for example, when comparing two different element carriers having the same Max CQI value, the larger the amount of traffic load, the smaller the metric value. Therefore, since the resource is not allocated to the element carrier having a small metric value, the traffic load can be considered. In another example, when two element carriers having the same traffic addition are compared, the channel state can be considered because the metric value becomes larger as the CQI value is larger.

However, since the ranges of the values of the traffic load and the channel state are different in S430, Equation (1) can be corrected to match the range of values. For example,

, The range of the value is [0, 1], and the value of Max CQI is [0, 15]. Therefore, it is necessary to calibrate both parameters to account together, but two embodiments are possible according to the invention.

In one embodiment, Equation (1) can be corrected as Equation (2) below.

In Equation (2), the correction factor

Is selected as a value capable of normalizing the value of Max CQI since the range of the value selected by Max CQI is larger than the traffic load.

In another embodiment, Equation (1) can be corrected as Equation (3) below.

In Equation (3), the correction factor

Is selected such that the scale of the Max CQI is equal to the scale of the traffic load.

5 is a configuration diagram of an element carrier scheduling apparatus in a carrier aggregation system according to an embodiment of the present invention.

Referring to FIG. 5, the element carrier scheduling apparatus includes a traffic load check unit 510, a channel state check unit 520, a metric calculation unit 530, and an element carrier allocation unit 540.

The traffic load check unit 510 checks the traffic load of each of the element carriers, and the channel state check unit 520 checks the channel state of each element carrier.

The metric calculator 530 calculates the value of the traffic load and the channel state of each of the element carriers output from the traffic load verifier 510 and the channel state verifier 520 using Equation (1) And calculates a PLB (Proportional Load Balancing) metric for each of all the element carriers available for the UE.

Since the ranges of the values of the traffic load and the channel state are different from each other, the metric calculator 530 can calculate the PLB (Proportional Load Balancing) metric using a formula that corrects Equation (1) have. For example,

, The range of the value is [0, 1], and the value of Max CQI is [0, 15]. Therefore, it is necessary to compensate for considering both parameters together. Two embodiments using the above-described Equations (2) and (3) according to the present invention are possible.

The metric calculation unit 540 allocates the element carrier having the highest value among the PLB (Proportional Load Balancing) metric values for all the calculated element carriers. That is, for example, when comparing two different element carriers having the same Max CQI value, the larger the amount of traffic load, the smaller the metric value. Therefore, since the resource is not allocated to the element carrier having a small metric value, the traffic load can be considered. In another example, when two element carriers having the same traffic addition are compared, the channel state can be considered because the metric value becomes larger as the CQI value is larger.

The present invention considers both the traffic load and the channel state together so that element carriers with a good channel condition can be selected if the traffic load is large. That is, according to the present invention, considering the channel state and the amount of the load for each element carrier, it is not to be concentrated on the element carrier having a large load, and at the same time, the resource is allocated considering the channel state for each element carrier, This will be described with reference to the performance result graphs shown in FIG. 6 and FIG.

6 is a graph showing a Jain's Fairness Index graph according to the present invention.

In FIG. 6, BestCQI is a scheduling method considering only channel gain (Channel Gain) of the PLB equation, and LeastLoad is a scheduling method considering only traffic load.

Jain's Fairness Index

, Which means that as all users transmit the same amount of traffic, they get closer to 1, and that the fairness index is high means that the amount of traffic transmitted by each user is evenly distributed without any deviation. The PLB-based scheduling scheme has better fairness performance than BestCQI and LeastLoad, except when 10 UE is allocated to all UEs in the performance result graph.

7 is a diagram illustrating cell total throughput according to the present invention.

Referring to FIG. 7, it can be seen that the proposed PLB scheme is located between BestCQI and LeastLoad in terms of cell total throughput, which is superior in terms of data rate.

Through the results shown in FIGS. 6 and 7, it can be seen that the proposed scheme has excellent cell throughput performance while dispersing the traffic load.

Claims (8)

Confirming the traffic load of each of the element carriers;
Confirming the channel condition of each of the element carriers;
Calculating a load balancing metric for each of the elementary carriers using the identified traffic load and channel conditions;
And comparing the calculated values of the load balancing metrics to assign the element carrier having the highest value to the terminal.
2. The method of claim 1, wherein the calculating
Wherein a value obtained by dividing the value of the channel state by a value of traffic load is calculated as a load balancing metric.
2. The method of claim 1, wherein the calculating
The traffic load

And the channel state is defined as a maximum channel quality indicator (Max CQI (Channel Quality Indicator)), the load balancing metric is defined as Max CQI

And multiplying the value by a first correction factor capable of normalizing a value of Max CQI.
2. The method of claim 1, wherein the calculating
The traffic load

And the channel state is defined as a maximum channel quality indicator (Max CQI (Channel Quality Indicator)), then the load balancing metric is defined as Max CQI

Is a value obtained by subtracting a value obtained by multiplying a scale of Max CQI by a second correction factor that makes the scale of the traffic load equal.
A traffic load confirmation unit for confirming a traffic load of each of the element carriers,
A channel state checking unit for checking the channel state of each of the element carriers,
A metric calculator for calculating a load balancing metric for each of the element carriers using the identified traffic load and channel conditions;
And an element carrier estimator for comparing the calculated values of the load balancing metrics and assigning an element carrier having a highest value to a user terminal.
6. The apparatus of claim 5, wherein the metric calculation unit
And calculating a value obtained by dividing the value of the channel state by the value of the traffic load as a load balancing metric.
6. The apparatus of claim 5, wherein the metric calculation unit
The traffic load

And the channel state is defined as a maximum channel quality indicator (Max CQI (Channel Quality Indicator)), the load balancing metric is defined as Max CQI

And a value obtained by multiplying a value obtained by dividing the maximum CQI by a first correction factor capable of normalizing a value of Max CQI.
6. The apparatus of claim 5, wherein the metric calculation unit
The traffic load

And the channel state is defined as a maximum channel quality indicator (Max CQI (Channel Quality Indicator)), then the load balancing metric is defined as Max CQI

Is a value obtained by subtracting a value obtained by multiplying a scale of Max CQI by a second correction factor that makes the scale of the traffic load equal.

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