KR102096155B1 - Handover Method in CA Configuration and Terminal which Performs Handover - Google Patents

Abstract

A handover method in a CA environment and a terminal performing handover are disclosed. The disclosed method includes the steps of: (a) determining whether the strength of the signal received by the terminal from the serving primary cell is equal to or greater than the first threshold value; If the strength of the signal received by the terminal is greater than or equal to the first threshold value, whether the strength of the received signal from the serving primary cell is equal to or less than a second threshold value greater than the first threshold value and from the serving primary cell Determining whether the amount of change in the received signal strength is negative (b); When the condition of step (b) is satisfied, the amount of change in the received signal strength is positive using the result of measuring the received signal strength from surrounding primary cells, and the strength of the received signal is greater than or equal to a third boundary value greater than the second boundary value. Generating a list of primary cells (c); And determining a primary cell having the smallest change in received signal strength among neighboring primary cells included in the list as a primary cell to perform handover. According to the disclosed invention, it is possible to minimize the throughput (Throughput) loss in an environment where the CA technology is used, there is an advantage to minimize the delay due to handover in a dense cell environment.

Description

Handover Method in CA Configuration and Terminal which Performs Handover}

The present invention relates to a handover method, and more particularly, to a handover method in a CA environment and a terminal performing the same.

Cell density is expected to continue to increase in a heterogeneous network environment to accommodate the growing mobile traffic. When the terminal moves in a dense network environment, the frequency of handover is expected to increase more, and the delay due to handover is also expected to increase.

During the handover delay, data transmission is stopped because handover signaling and radio link switching occur. In particular, in recent years, CA (Carrier Aggregation) technology is used, and in the environment where CA technology is used, throughput loss due to handover delay is expected to be further intensified.

In the CA environment, there is a primary cell and a secondary cell. Whenever a handover occurs between primary cells, a connection to the secondary cell must be made, and when a secondary cell is connected, an activation delay is generated in addition to the handover delay. In this environment, the throughput loss due to handover is exacerbated.

Therefore, it is difficult to expect smooth communication in the future network environment with the existing handover policy of performing handover with the base station having the strongest signal strength.

The present invention proposes a handover method capable of minimizing throughput loss in an environment where CA technology is used and a terminal performing the same.

In addition, the present invention proposes a handover method capable of minimizing the delay due to handover in a cell dense environment and a terminal performing the same.

According to an aspect of the present invention, determining whether the strength of the signal received by the terminal from the serving primary cell is greater than or equal to the first boundary value (a); If the strength of the signal received by the terminal is greater than or equal to the first threshold value, whether the strength of the received signal from the serving primary cell is equal to or less than a second threshold value greater than the first threshold value and from the serving primary cell Determining whether the amount of change in the received signal strength is negative (b); When the condition of step (b) is satisfied, the amount of change in the received signal strength is positive using the result of measuring the received signal strength from the surrounding primary cells and the intensity of the received signal is greater than or equal to a third boundary value greater than the second boundary value. Generating a list of primary cells (c); A handover method is provided in a CA (Carrier Aggregation) environment including the step (d) of determining a primary cell having the smallest change in received signal strength among neighboring primary cells included in the list as a primary cell to perform handover. do.

In the handover method, when the strength of the signal received by the terminal from the serving primary cell is equal to or less than the first threshold value, searching for a neighboring primary cell in which the amount of change in received signal strength from neighboring primary cells is positive (e). ; A step (f) of searching for a neighboring primary cell in which the strength of a received signal is greater than or equal to a first threshold among the neighboring primary cells searched in step (e); The step (g) of determining the primary cell having the smallest change in the received signal strength among the neighboring primary cells searched in step (f) as a primary cell to perform handover is further included.

The handover method performs handover to the primary cell having the largest received signal strength in step (f) when there is no peripheral primary cell having a received signal strength greater than or equal to a first threshold among the peripheral primary cells. Further comprising the step (h) to determine the primary cell to be.

The handover method includes: receiving optimal number of auxiliary cells to be connected from the terminal; And when the handover to another primary cell is completed, controlling the terminal to make a connection between the terminal and the auxiliary cell based on the number of auxiliary cells.

The number of auxiliary cells to be connected is determined to minimize the handover cost of the auxiliary cells.

The handover cost of the auxiliary cell is determined by the movement speed of the terminal, the distance at which a signal having an intensity corresponding to the first boundary value is received, and the activation delay of the auxiliary cell due to the handover of the primary cell.

The number of auxiliary cells to be connected is determined as follows.

In the above equation, Ds is the handover cost of the auxiliary cell, v is the mobile speed of the terminal, x _THcover is the distance at which a signal of an intensity corresponding to the first boundary value is received, and d _s is the handover of the primary cell Is the activation delay of the secondary cell, d1 and d2 are randomly determined constants, and d _p is the handover delay of the primary cell.

According to another aspect of the invention, the handover performing unit for performing a handover under the control of the primary cell; Auxiliary for determining the number of auxiliary cells connected to minimize the movement speed of the terminal, the distance at which a signal having an intensity corresponding to the first boundary value is received, and the handover cost of the auxiliary cell determined by the handover delay of the auxiliary cell Cell number determination unit; And a storage unit for storing received signal strength from the serving primary cell and received signal strength information from the neighboring primary cell, wherein the handover performing unit is the first boundary value and a second boundary value greater than the first boundary value. , A terminal for handover in a CA environment that performs handover to a primary cell determined to perform handover using a third boundary value greater than the second boundary value and a change in received signal strength from neighboring primary cells Is provided.

According to embodiments of the present invention, there is an advantage that can minimize the throughput (Throughput) loss in the environment where the CA technology is used. In addition, according to embodiments of the present invention, there is an advantage in that the delay due to handover can be minimized in an environment in which a cell is dense.

1 is a view showing a mobile communication system using a CA (Carrier Aggregation) technology to which the present invention is applied.
2 is a conceptual diagram showing a handover method according to an embodiment of the present invention.
3 is a flowchart illustrating the overall flow of a handover method according to an embodiment of the present invention.
4 is a block diagram showing a configuration of a terminal performing handover according to an embodiment of the present invention.
5 is a diagram showing a structure of a packet for transmitting information on the optimal number of secondary cells determined by the UE to the serving primary cell;

Other advantages and features of the present invention, and methods for achieving them will be clarified with reference to embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only the present embodiments allow the disclosure of the present invention to be complete, and the general knowledge in the technical field to which the present invention pertains. It is provided to fully inform the holder of the scope of the invention, and the invention is only defined by the scope of the claims.

If not defined, all terms (including technical or scientific terms) used herein have the same meaning as generally accepted by universal technology in the prior art to which this invention belongs. Terms defined by general dictionaries can be interpreted as having the same meaning as meaning in the text of the present application and / or related descriptions, and are not conceptualized or over-formally interpreted, even if not explicitly defined herein. Will not. The terminology used herein is for describing the embodiments and is not intended to limit the present invention.

1 is a view showing a mobile communication system using a CA (Carrier Aggregation) technology to which the present invention is applied.

The present invention relates to a handover method in a mobile communication system to which CA (Carrier Aggregation) technology is applied in a heterogeneous network environment.

Referring to FIG. 1, a mobile communication system to which CA technology is applied includes a primary cell 100 and a plurality of secondary cells (Secondary Cell, 1, 2, ..., s-1, s). CA technology is a technology introduced in LTE release 10, and is a technology capable of expanding bandwidth in which one terminal downloads or uploads data by combining multiple component carriers (CCs) through CA. A CA-capable terminal has one primary component carrier 101 in the downlink and a primary component carrier (PCC) in the corresponding uplink. In addition, one or more secondary component carriers (SCCs) 102 may be additionally included in each link. PCC is used for communication with the primary cell 100, and SCC is used for communication with the secondary cell.

A handover may be performed to change the connected primary cell 100 according to a change in the channel state according to the movement of the terminal. Handover to the primary cell 100 affects the activation state of the secondary cell. This is because when a handover is performed from one primary cell to another primary cell, connection establishment for secondary cells is performed again.

The primary cell newly connected through the handover should activate new auxiliary cells in consideration of the channel state of the auxiliary cells. During this process, after handover of the primary cell, a delay occurs while activating the secondary cell. Of course, even if the handover for the primary cell does not occur, activation for the new secondary cell may occur, and a delay may be caused.

In the future communication environment, handover between primary cells is expected to occur more frequently due to cell density, and as the number of connectable secondary cells increases, the delay in activating secondary cells due to handover of primary cells is also expected to increase. do.

2 is a conceptual diagram showing a handover method according to an embodiment of the present invention.

For convenience of description, FIG. 2 shows a handover method according to a conventional A3 method.

Referring to FIG. 2, handover according to the conventional A3 method performs handover based on the strength of the received signal (RSRP) from each primary cell P1, P2, P3, P4, and P5. Since the conventional method performs handover only when a larger signal is received from the neighboring primary cell than the current serving primary cell, very frequent handover is inevitable when the terminal is moving. Particularly, handover occurs more frequently in an environment in which primary cells are concentrated.

Referring to Figure 2, according to the conventional A3 method, a total of five handovers occur according to the movement of the terminal.

As described above, in the CA environment, the handover method for solving this problem is proposed because the frequent handover causes a delay caused by the handover itself, as well as an auxiliary cell activation delay.

The present invention basically performs handover using three boundary values. The first boundary value is THcover 204, which is the lowest boundary value. The second boundary value is set to be larger than the first boundary value as THout 203. The third boundary value is THin 202, which is set larger than the first and second boundary values.

Unlike the conventional handover that considers only the strength of the received signal from each primary cell, the present invention performs handover using three boundary values and a variation in the strength of the received signal.

For such handover, the channel state and the received signal strength with the primary cell should be acquired, and the Okumura-Hata model was used as the path loss model for obtaining the received signal strength (RSRP) value, and the serving primary cell The received signal strength of the terminal U _h from H _y may be expressed by Equations 1 to 6 below.

In the above equation, RSRP (H _y , U _h ) means the received signal strength [W] of the terminal U _h , and P (H _y ) represents the transmission power [dBm] of the serving primary cell. d represents the distance from the serving primary cell H _y to the terminal U _h , and f represents the frequency. h _b represents the height of the serving primary cell H _y , and h _m represents the height of the terminal U _h .

The present invention is used to determine the primary cell to handover the amount of change in RSRP obtained by the above method.

RSRP change amount may be defined as in Equation 7 below.

If the terminal is away from a specific primary cell, ΔRSRP is negative. Conversely, if the terminal is close to a specific primary cell, ΔRSRP is positive.

In the present invention, when determining the primary cell for handover, the primary cell having the longest cell connection time is selected. Here, the cell connection time means the time that the terminal stays within the cell. When handover is possible with any one of a plurality of primary cells, when performing handover with the primary cell farthest in the mobile direction of the terminal, handover may be made with the primary cell having the longest cell connection time. This means that when handover with multiple primary cells is possible, ΔRSRP selects the smallest primary cell.

In the present invention, a method for determining a primary cell to perform handover is expressed by Equation (8).

In Equation 8 above, m is an index indicating a primary cell, and m * means a selected primary cell.

Referring to FIG. 2, the serving primary cell is P1, and among the primary cells P2 to P5 capable of handover, P5, which is the smallest primary cell with ΔRSRP, is selected as a primary cell to perform handover. According to the handover policy according to the present invention, since only one handover occurs, the handover frequency can be significantly reduced compared to the A3 method.

Hereinafter, a detailed flow of a handover method using three boundary values and RSRP variation will be described with reference to FIG. 3.

3 is a flowchart illustrating the overall flow of a handover method according to an embodiment of the present invention.

Referring to FIG. 3, first, the UE transmits a measurement report to the current serving primary cell (step 302). The measurement report is made at predetermined time intervals. The measurement report includes RSRP information from the serving primary cell and RSRP information from the surrounding primary cell.

When receiving the measurement report received from the terminal, serving the primary cell is determined whether the terminal is the intensity of received signals from the serving primer reseller receiving (RSRP _Pcell) is more than the first threshold value (THcover) (step 303) . The first boundary value is set to a minimum RSRP value capable of maintaining a smooth communication state without generating a radio link failure (RLF).

The first boundary value is used as a value for determining whether to perform emergency handover. If the RSRP from the serving primary cell is greater than or equal to the first threshold, normal handover of steps 304 to 306 is performed. However, when the RSRP from the serving primary cell is less than or equal to the first boundary value, there is a high possibility of radio link failure, and thus the emergency handover of steps 307 to 312 is performed.

If the received signal received by the terminal from the serving a primary cell than the first threshold, it is determined whether or not ΔRSRP _Pcell is negative, yet _Pcell RSRP is below a second threshold value (THout) (step 304). Step 304 by the method comprising: determining whether or not to prepare a handover ΔRSRP _Pcell is negative and RSRP _Pcell the claim if more than two threshold terminal As moving away from the serving a primary cell RSRP _Pcell is determined low, so the handover required handover Steps 304 to 306 are performed to determine and prepare.

To prepare for handover, RSRP values of neighboring primary cells, excluding the serving primary cell, are measured during the Δt frame and provided to the serving primary cell, and the serving primary cell generates a target primary cell list (step 305). Among the neighboring primary cells, primary cells in which ΔRSRP is positive and RSRP is THin, which is a third threshold or higher, are included in the target primary cell list.

When the target primary cell list is generated, the primary cell having the smallest ΔRSRP among the target primary cells included in the list is determined as the primary cell to perform handover, and handover with the corresponding primary cell is performed (step 306). ). The primary cell to perform handover is determined by Equation (8).

If the RSRP from the serving primary cell is less than or equal to the first threshold value (THcover), an urgent handover is required, and in this case, it is determined whether there is a cell with a positive ΔRSRP among the neighboring primary cells (step 307).

If there are peripheral primary cells with a positive ΔRSRP, it is determined whether or not a cell having a RSRP of a first threshold or higher is present (step 308).

Among cells with RSRP above the first threshold, the primary cell with the lowest ΔRSRP is determined as a cell to perform handover (step 309).

If there are peripheral primary cells with a positive ΔRSRP, but there are no cells with a RSRP above a first threshold among the primary cells, handover is performed to the cell having the largest RSRP (step 311).

On the other hand, when ΔRSRP is positive in the vicinity and there is no peripheral primary cell having RSRP equal to or greater than the first threshold (step 310), handover is not performed.

As described above, the handover method of the present invention allows the cell connection time to be maximized by using the first to third boundary values and the change amount (ΔRSRP) of RSRP. It has the advantage of minimizing the delay in a dense cell head environment.

On the other hand, when the handover method of the present invention is applied, it is possible to reduce the frequency of handover, but communication is performed at a low RSRP, so that the average throughput may be lowered. Since CA technology is applied, the reduction in average throughput can be compensated by additionally connecting auxiliary cells.

However, it is necessary to connect an appropriate number of auxiliary cells because connection with a plurality of auxiliary cells causes an activation delay of the auxiliary cells and increases signaling overhead. The present invention proposes a method for determining the appropriate number of auxiliary cells connected to a terminal together with a handover method.

The present invention determines the number of auxiliary cells in consideration of the handover cost and the average throughput in order to optimize the number of auxiliary cells to be connected.

The handover cost refers to a normalized handover delay, and specifically, the ratio of data transmission disconnection time caused by handover signaling and radio link switching between the serving primary cell and the primary cell to be handover occupies the total connection time. And the handover cost can be defined as in Equations 9 and 10 below.

는 단위 거리 동안 발생한 핸드오버 횟수를 의미하고, v는 단말의 이동속도를 나타낸다. In the above equation, D denotes a handover cost, H _t denotes a handover incidence rate for a unit time, and d denotes a handover delay. Also,

Denotes the number of handovers occurring during a unit distance, and v denotes the moving speed of the terminal.

The present invention determines the number s * of auxiliary cells connected in a direction to minimize the handover cost (Ds) of the auxiliary cells. In order to determine the number of secondary cells to be connected, x _THcover , a distance at which the RSRP of the first threshold value THcover is received from the serving primary cell, and the speed of the UE and the delay of activation of the secondary cell due to handover of the primary cell d _s is used. d _s is determined by the number (s) of auxiliary cells to be connected.

The number of auxiliary cells may be determined as shown in Equation 11 below.

In Equation 11 above, v denotes a moving speed of the terminal.

In Equation 11, d _s is a function of s, which is the number of auxiliary cells to be connected, and Ds can be redefined as in Equation 12 below.

In Equation 12 above, d1 and d2 are randomly determined constants, and d _p is a handover delay of the primary cell.

The present invention determines the number of auxiliary cells connected so as to minimize the handover cost of the auxiliary cells as shown in Equation (11).

Determination of the number of auxiliary cells is made when a handover is performed from a serving primary cell to another primary cell, and the terminal transmits the determined number of auxiliary cells to the primary cell. When the handover is completed, the serving primary cell controls the terminal to establish a connection between the terminal and the auxiliary cell based on the determined number of auxiliary cells.

4 is a block diagram showing the configuration of a terminal performing handover according to an embodiment of the present invention.

Referring to FIG. 4, a terminal according to an embodiment of the present invention may include an auxiliary cell number determining unit 400, a handover performing unit 410, a storage unit 420, and a control unit 430.

Auxiliary cell count determining unit x _THcover , the distance at which the RSRP of the first threshold value THcover is received from the serving primary cell according to the above-described method, the speed of the terminal and the activation delay of the auxiliary cell due to handover of the primary cell d _The optimal number of auxiliary cells is determined using _s . As described above, the optimal number of auxiliary cells is determined in a direction to minimize the handover cost of the auxiliary cells.

The handover performing unit 410 performs handover under the control of the serving primary cell and performs connection with the determined number of auxiliary cells.

The storage unit 420 stores measurement reports transmitted to the serving primary cell and information necessary for handover. Specifically, the storage unit stores received signal strength information from a serving primary cell and received signal strength information from neighboring primary cells included in the measurement report.

In the control unit 430, the auxiliary cell number determining unit 400, the handover performing unit 410, and the storage unit 420 control operations.

 5 is a diagram showing the structure of a packet that transmits information on the optimal number of auxiliary cells determined by the terminal to the serving primary cell.

Referring to FIG. 5, the flag field is a field indicating whether to use an existing handover technique (eg, A3) or the handover method of the present invention. For example, the flag field may be set to 0 (602) when using the existing handover technique, and the flag field may be set to 1 (603) when using the handover technique of the present invention.

When the handover technique of the present invention is used, the optimal number of auxiliary cells s * connected to the first threshold value THcover is recorded in the option field 604.

The flag field 601 is composed of three bits, and a DF (don't fragment) and a MF (more fragment) may be used according to existing uses. Meanwhile, FIG. 5 shows a case where the number of bits in the option field is 16 bits, but the number of bits may be changed according to a use environment and a system.

It is to be understood that the above embodiments are provided to help the understanding of the present invention, and do not limit the scope of the present invention, and various modified embodiments may belong to the scope of the present invention. For example, each component shown in the embodiments of the present invention may be implemented in a distributed manner, or conversely, multiple components may be implemented in combination. Therefore, the technical protection scope of the present invention should be determined by the technical spirit of the claims, and the technical protection scope of the present invention is not limited to the literary description of the claims, but is substantially equal in technical value. It should be understood that it extends to a range of inventions.

Claims (11)

Determining whether the strength of the signal received by the terminal from the serving primary cell is equal to or greater than the first threshold value (a);
If the strength of the signal received by the terminal is greater than or equal to the first threshold value, whether the strength of the received signal from the serving primary cell is equal to or less than a second threshold value greater than the first threshold value and from the serving primary cell Determining whether the amount of change in the received signal strength is negative (b);
When the condition of step (b) is satisfied, the amount of change in the received signal strength is positive using the result of measuring the received signal strength from the neighboring primary cells and the intensity of the received signal is greater than or equal to the third boundary value greater than the second boundary value. Generating a list of primary cells (c);
And determining a primary cell having the smallest change in received signal strength among neighboring primary cells included in the list as a primary cell to perform handover. (D) A hand in a CA (Carrier Aggregation) environment. Over method.
According to claim 1,
If the intensity of the signal received by the terminal from the serving primary cell is less than or equal to a first threshold value, searching for a neighboring primary cell in which the amount of change in received signal strength from neighboring primary cells is positive (e);
A step (f) of searching for a neighboring primary cell in which the strength of a received signal is greater than or equal to a first threshold among the neighboring primary cells searched in step (e);
Further comprising the step (g) of determining the primary cell with the smallest variation in the received signal strength among the neighboring primary cells searched in step (f) as a primary cell to perform handover, CA (Carrier Aggregation), characterized in that ) Handover method in the environment.
According to claim 2,
In step (f), if there is no neighboring primary cell in which the strength of the received signal is greater than or equal to a first threshold value among the neighboring primary cells, the primary cell having the largest received signal strength is determined as a primary cell to perform handover. Handover method in a CA (Carrier Aggregation) environment, characterized in that it further comprises a step (h).
According to claim 3,
Receiving (i) an optimal number of auxiliary cells to be connected from the terminal; And
When the handover to another primary cell is completed, further comprising (j) controlling the terminal to establish a connection between the terminal and the auxiliary cell based on the number of auxiliary cells. ) Handover method in the environment.
According to claim 4,
The number of auxiliary cells to be connected is determined to minimize the handover cost of the auxiliary cell,
The handover cost of the auxiliary cell is determined by the mobile speed, the distance at which the signal corresponding to the first boundary value is received, and the activation delay of the auxiliary cell due to the handover of the primary cell. Handover method in CA environment.

delete The method of claim 5,
The handover method in the CA environment, characterized in that the number of auxiliary cells to be connected is determined by the following equation.

In the above equation, Ds is the handover cost of the auxiliary cell, v is the mobile speed of the terminal, x _THcover is the distance at which a signal of an intensity corresponding to the first boundary value is received, and d _s is the handover of the primary cell Is the activation delay of the secondary cell, d1 and d2 are randomly determined constants, and d _p is the handover delay of the primary cell.
A handover performing unit performing handover under the control of the primary cell;
Auxiliary cells to determine the number of auxiliary cells connected to minimize the movement speed of the terminal, the distance at which a signal having an intensity corresponding to the first boundary value is received, and the handover cost of the auxiliary cell determined by the handover delay of the auxiliary cell Number determining unit; And
It includes a storage unit for storing the received signal strength from the serving primary cell and the received signal strength information from the neighboring primary cell,
The handover performing unit performs handover using the first boundary value, the second boundary value greater than the first boundary value, the third boundary value greater than the second boundary value, and the amount of change in received signal strength from neighboring primary cells. Handover to the primary cell determined to perform the,
The handover cost of the auxiliary cell is determined by the mobile speed, the distance at which the signal corresponding to the first boundary value is received, and the activation delay of the auxiliary cell due to the handover of the primary cell. Terminal for handover in CA environment.
The method of claim 8,
The auxiliary cell number determining unit determines the number of auxiliary cells to be connected as shown in the following equation: a terminal for handover in a CA environment.

In the above equation, Ds is the handover cost of the auxiliary cell, v is the mobile speed of the terminal, x _THcover is the distance at which a signal of an intensity corresponding to the first boundary value is received, and d _s is the handover of the primary cell Is the activation delay of the secondary cell, d1 and d2 are randomly determined constants, and d _p is the handover delay of the primary cell.
The method of claim 8,
The serving primary cell,
Determining whether the strength of the signal received by the terminal from the serving primary cell is equal to or greater than the first threshold value (a);
If the strength of the signal received by the terminal is greater than or equal to the first threshold value, whether the strength of the received signal from the serving primary cell is equal to or less than a second threshold value greater than the first threshold value and from the serving primary cell Determining whether the amount of change in the received signal strength is negative (b);
When the condition of step (b) is satisfied, the amount of change in the received signal strength is positive using the result of measuring the received signal strength from the neighboring primary cells and the intensity of the received signal is greater than or equal to the third boundary value greater than the second boundary value. Generating a list of primary cells (c);
Determining the primary cell to perform the handover by performing the step (d) of determining the primary cell with the smallest change in the received signal strength among the neighboring primary cells included in the list as the primary cell to perform the handover. Terminal for handover in a CA environment characterized by.
The method of claim 10,
The serving primary cell,
If the intensity of the signal received by the terminal from the serving primary cell is less than or equal to a first threshold value, searching for a neighboring primary cell in which the amount of change in received signal strength from neighboring primary cells is positive (e);
A step (f) of searching for a neighboring primary cell in which the strength of a received signal is greater than or equal to a first threshold among the neighboring primary cells searched in step (e);
The hand in the CA environment characterized by further performing the step (g) of determining the primary cell having the smallest change in the received signal strength among the neighboring primary cells searched in step (f) as a primary cell to perform handover. Terminal for over.

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