CN104581849B - A kind of cell switching method - Google Patents

Abstract

The invention relates to a cell switching method and belongs to the technical field of wireless communication. It includes the following steps: 1) The UE continuously detects the reference signal received power RSRP of the current serving cell and the adjacent cell, and performs data smoothing on the RSRP to determine whether the handover trigger condition is met. If so, the trigger time TTT timer starts counting and executes Step 2), otherwise continue to detect RSRP; 2) UE sends a pre-handover request message to the current serving cell, and the current serving cell determines the UE pre-handover candidate cell set according to the received message; 3) The current serving cell notifies the pre-handover candidate cell to perform pre-handover Handover preparation; 4) If the TTT fails and the UE detects that the handover trigger condition is still satisfied, it will send a handover instruction to the current serving cell; 5) The current serving cell determines the handover target cell according to the measurement report; 6) The current serving cell notifies the handover target cell Execute the switch. The method can effectively reduce the ping-pong effect and the handover delay, and improve the QoS experience of the handover user.

Description

A kind of cell switching method

technical field

The invention belongs to the technical field of wireless communication, and relates to a cell switching method.

Background technique

With the rapid development of wireless communication technology, all kinds of smart terminals are showing explosive growth trend, and rich and diverse data services are also emerging. The high-speed service needs of users pose a severe challenge to traditional cellular networks. Heterogeneous cellular network technology introduces low-power nodes, such as relay sites, picocell sites, and home base stations, within the coverage of traditional macrocells, to strengthen the coverage of specific areas in a targeted manner and form multi-layer network coverage, which can effectively realize User QoS guarantee improves system resource utilization. The network characteristics such as irregular deployment of low-power nodes and large differences in coverage in heterogeneous cellular networks, as well as the different characteristics of user movement speed and service requirements, all pose difficulties and challenges to the handover control technology of heterogeneous cellular networks.

At present, some studies have considered the performance improvement scheme of user handover in heterogeneous cellular network. For example, a pre-handover preparation mechanism is proposed in the proposal [3GPP Tdoc R2-132375.Performance Analysis on EarlyHOPreparation and EarlyHO CMD.ZTECorporation.2013]. The current serving cell sends a pre-handover preparation message to the pre-handover candidate cell before handover execution, informing the pre-handover candidate cell to reserve resources, thereby effectively reducing the probability of handover failure, but this scheme does not consider how to select the pre-handover candidate cell, which may cause Non-potential handover candidate cells perform pre-handover preparations, resulting in waste of cell channel resources and large signaling overhead. In addition, in existing studies, the selection of the target cell mainly considers the received signal strength of the user, and does not consider the service characteristics after the user switches to the target cell, which may lead to the inability to guarantee the user's QoS experience. Therefore, how to design an efficient handover method by comprehensively considering multiple factors such as user handover success rate, handover candidate cell and target cell characteristics, and user QoS experience has become an urgent problem to be solved.

Contents of the invention

In view of this, the object of the present invention is to provide a cell handover method, the method is as follows:

A cell switching method, comprising the following steps:

Step 1: The user equipment (UE) continuously detects the reference signal received power RSRP of the current serving cell and the adjacent cell, and performs data smoothing on the RSRP to determine whether the handover trigger condition is met. If so, start the trigger time (TTT) timer, and Execute step 2, otherwise, continue to detect RSRP;

Step 2: The UE sends a pre-handover request to the current serving cell, including its own status and the status of neighboring cells; the current serving cell determines the UE pre-handover candidate cell set according to the received message;

Step 3: The current serving cell notifies the pre-handover candidate cell to perform pre-handover preparation;

Step 4: If the TTT fails and the UE detects that the handover trigger condition is still satisfied, it sends a handover instruction to the current serving cell, which includes the current cell and neighboring cell measurement reports;

Step 5: The current serving cell determines the handover target cell according to the measurement report;

Step 6: The current serving cell notifies the handover target cell to perform the handover.

Further, in step 1, the UE continuously detects the reference signal received power RSRP of the current serving cell and neighboring cells, and obtains the smoothed reference signal received power RSRP ^s (t) by passing the RSRP through an exponential average filter, and the filter model used is as follows :

RSRP ^s (t) = kRSRP ^r (t-1) + (1-k)RSRP ^r (t)

Among them, RSRP ^s (t) represents the output value of the filter at time t, RSRP ^r (t) represents the received power of the reference signal received at time t, that is, the input value of the filter, and k represents the smoothing parameter of the filter.

Further, the handover trigger condition is that the smoothed RSRP difference between the adjacent cell and the current serving cell is higher than the trigger threshold; if Indicates the smoothed RSRP of the current serving cell, with Indicates the smoothed RSRP of the i-th adjacent cell, and the handover trigger condition is expressed as: there is i, and Wherein, RSRP _th is the trigger threshold.

Further, in step 2, the pre-handover request message sent by the UE to the current serving cell includes its own status and the status of neighboring cells, wherein the UE's own status includes the current moving speed and direction of the UE.

Further, in step 2, the current serving cell determines the UE pre-handover candidate cell set according to the state of the UE itself and the state of neighboring cells, specifically including:

1) The current serving cell judges whether to perform handover according to the moving speed of the UE. If the UE speed V≤V _th , and V _th is the moving speed threshold value, then step 2) can be performed; otherwise, the current serving cell stops selecting pre-handover candidates for the UE District;

2) The current serving cell performs the first screening of adjacent cells according to the RSRP difference between the adjacent cell and the current serving cell reported by the UE, as follows: the difference between the RSRP of the adjacent cell and the current serving cell and the preset ΔRSRP _th is compared, if it is greater than ΔRSRP _th , the adjacent cell can be used as a pre-handover candidate cell; otherwise, the adjacent cell is not a pre-handover candidate cell;

3) The angle between the current serving cell and the adjacent cell according to the moving direction of the UE The second screening is performed on the pre-handover candidate cells, as follows: Indicates the angle between the connection line between the i-th handover candidate cell base station and the UE and the moving direction of the UE, if Then confirm that the cell is a user pre-handover candidate cell; if Then the cell is not used as a pre-handover candidate cell. After secondary screening, the UE pre-handover candidate cell set can be obtained.

Further, in step 3, the current serving cell notifies the pre-handover candidate cell to perform pre-handover preparation, specifically including:

1) The current serving cell sends a pre-handover preparation message to the pre-handover candidate cell;

2) The pre-handover candidate cell receives the pre-handover preparation message, performs resource reservation, and sends a pre-handover preparation response message to the current serving cell;

3) The current serving cell receives the pre-handover preparation response message, and sends a pre-handover request response message to the UE.

Further, in step five, the current serving cell determines the handover target cell according to the measurement report, specifically including:

1) The current serving cell acquires the smoothed pre-handover candidate cell received at the UE and available bandwidth B _i of pre-handover candidate cells, 1≤i≤N, where N is the number of pre-handover candidate cells;

2) The current serving cell estimates the transmission rate of the UE after switching to the pre-handover candidate cell according to the UE pre-handover candidate cell information, and uses R _i to identify the transmission rate of the UE after switching to the i-th cell, which can be obtained

in, is the RSRP of the j-th cell with the same frequency as the i-th cell arriving at the UE, N _i is the number of cells with the same frequency as the i-th cell, and ^σ2 is the noise power; the current serving cell selects the pre-handover with the highest transmission rate The candidate cell is used as the handover target cell, namely: i ^* =argmaxR _i .

The beneficial effects of the present invention are:

1) The present invention can more accurately estimate the received power RSRP of each cell received by the UE, reduce the impact of data mutation on handover decision, and effectively avoid the ping-pong effect.

2) The pre-handover candidate cell selection method in the present invention can effectively reduce the number of pre-handover preparation cells, thereby reducing waste of cell reserved resources and signaling overhead.

3) The target cell selection method in the present invention selects the target cell based on the transmission rate of the UE after switching to the target cell, so as to effectively guarantee the QoS experience of the switched UE.

Description of drawings

In order to make the purpose, technical scheme and beneficial effect of the present invention clearer, the present invention provides the following drawings for illustration:

Figure 1 is a schematic diagram of a heterogeneous cellular network scenario;

Fig. 2 is a schematic flow chart of the method of the present invention.

Detailed ways

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Figure 1 is a schematic diagram of a heterogeneous cellular network scenario. In the figure, there are seven low-power cells in a macro cell coverage area, and each low-power cell does not share the frequency band with the macro cell. Among them, cells A, C and F share the frequency band f _1. Cells B, E, and G share the frequency band f ₂ , and cell D exclusively uses the frequency band f ₃ . When the UE is moving, it detects the reference signal received power (RSRP) of the macro cell and the low-power cell. If the UE detects that the handover trigger condition is met and the condition is still met after the trigger time (TTT), execute switch.

Fig. 2 is a flow chart of the cell handover method proposed by the present invention. As shown in the figure, the cell switching method of the present invention is specifically as follows:

S1: The current serving cell sends a measurement control message to the UE, and the UE configures measurement parameters through the measurement control message, and periodically detects the current serving cell and neighboring cells.

S2: The UE detects whether a handover trigger condition is satisfied. The switching trigger condition is defined as: in, Indicates the smoothed RSRP value of the current serving cell, Indicates the smoothed RSRP value of the i-th neighboring cell. The UE uses an exponential average filter to obtain the smoothed reference signal received power RSRP ^s (t), and the filter model used is: RSRP ^s (t)=kRSRP ^r (t-1)+(1-k)RSRP ^r (t) . If the handover trigger condition is met, the UE sends a pre-handover request message to the current serving cell, and the TTT timer starts counting; otherwise, the UE continues to detect the RSRP values of the current serving cell and neighboring cells.

S3: The UE sends a pre-handover request message to the current serving cell, which includes the UE's own moving speed and moving direction. The current serving cell selects a candidate cell for pre-handover according to the mobile state of the UE. The specific selection process is as follows: (1) The current serving cell judges whether to perform handover according to the mobile speed of the UE; if V≤V _th , then perform step (2); otherwise, the current The serving cell terminates to select a pre-handover candidate cell set for the UE; (2) The current serving cell performs initial screening on the adjacent cells according to the RSRP difference between the adjacent cells reported by the UE and the current serving cell. The current serving cell RSRP difference is compared with a preset threshold value ΔRSRP _th , if it is greater than ΔRSRP _th , the adjacent cell can be used as a pre-handover candidate cell; otherwise, the adjacent cell is not used as a pre-handover candidate cell; ( 3) The angle between the current serving cell and the adjacent cell according to the moving direction of the UE Perform secondary screening on the pre-handover candidate cells, and the screening preparations are as follows: Indicates the angle between the connection line between the i-th handover candidate cell base station and the UE and the moving direction of the UE, if Indicates that the UE is moving towards the adjacent cell, then confirm that the cell is a candidate cell for UE pre-handover; if It means that the UE is moving away from this cell, and this cell is not used as a pre-handover candidate cell. After secondary screening, the UE pre-handover candidate cell set can be obtained.

S4: The current serving cell sends a pre-handover preparation message to the pre-handover candidate cell after selecting a pre-handover candidate cell for the UE; the pre-handover candidate cell receives the pre-handover preparation message, performs resource reservation, and sends a pre-handover preparation message to the current serving cell The response message notifies the current serving cell that it is ready for handover; the current serving cell sends a pre-handover request response message to the UE after receiving the pre-handover preparation response, notifying the UE that the pre-handover preparation has been completed.

S5: The UE continues to detect the RSRP values of the current serving cell and the neighboring cell. If the TTT timer expires, the handover trigger condition is still met, that is, Then the UE sends a handover indication message to the current serving cell.

S6: After receiving the handover instruction, the current serving cell selects the target cell by considering the transmission rate of the UE after switching to the target cell, specifically: the current serving cell obtains the information of the pre-handover candidate cell at the UE value and the available bandwidth B _i of the pre-handover candidate cell, 1≤i≤N, where N is the number of neighbor cells of the UE; the current serving cell estimates the transmission rate of the UE after switching to the pre-handover candidate cell according to the information of the pre-handover candidate cell, expressed as R _i identifies the transmission rate after the UE switches to the i-th cell, which can be obtained

in, is the RSRP of the j-th cell with the same frequency as the i-th cell to the UE, N _i is the number of cells with the same frequency as the i-th cell, and ^σ2 is the noise power; the base station of the current cell selects the candidate handover cell with the highest transmission rate As the handover target cell, that is: i ^* =argmaxR _i .

S7: The current serving cell sends a handover indication response message to the UE, and starts to execute the handover process. After the handover process ends, the current serving cell sends a resource release message to other pre-handover candidate cells, notifying the other pre-handover candidate cells to release handover reserved resources.

Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that it can be described in terms of form and Various changes may be made in the details without departing from the scope of the invention defined by the claims.

Claims (1)

1. A method of cell handover, characterized by: the method comprises the following steps:

the method comprises the following steps: the User Equipment (UE) continuously detects the Reference Signal Received Power (RSRP) of the current service cell and the adjacent cell, and judges whether a switching trigger condition is met or not after data smoothing is carried out on the RSRP, if so, a Time To Trigger (TTT) timer is started, and the step two is executed, otherwise, the RSRP is continuously detected;

step two: UE sends a pre-switching request to a current service cell, wherein the pre-switching request comprises a self state and an adjacent cell state; the current service cell determines a UE pre-switching candidate cell set according to the received information;

step three: the current service cell informs the pre-switching candidate cell to execute pre-switching preparation;

step four: if the TTT is invalid and the UE detects that the switching triggering condition is still met, the UE sends a switching instruction to the current service cell, wherein the switching instruction comprises a measurement report of the current cell and an adjacent cell;

step five: the current service cell determines a switching target cell according to the measurement report;

step six: the current service cell informs the switching target cell to execute switching;

in step two, the pre-switching request message sent by the UE to the current service cell comprises a self state and an adjacent cell state, wherein the self state of the UE comprises the current moving speed and direction of the UE;

in step two, the current serving cell determines the UE pre-handover candidate cell set according to the UE self-state and the neighboring cell state, and specifically includes:

1) the current service cell judges whether to execute switching according to the UE moving speed, if the UE speed V is less than or equal to V_th，V_thIf the threshold value is the moving speed threshold value, step 2) can be executed; otherwise, the current service cell terminates selecting pre-switching candidate cells for the UE;

2) the current serving cell performs first screening on the neighboring cells according to the RSRP difference between the neighboring cells reported by the UE and the current serving cell, specifically as follows: the difference value of the RSRP of the adjacent cell and the current service cell is compared with the preset delta RSRP_thComparing, if greater than Δ RSRP_thThen the neighboring cell can be used as a pre-handover candidate cell; otherwise, the adjacent cell is not taken as a pre-switching candidate cell;

3) the current service cell forms an included angle with the adjacent cell according to the moving direction of the UEAnd performing secondary screening on the pre-switching candidate cell, specifically as follows: to be provided withIndicating the included angle between the connection line between the base station of the ith handover candidate cell and the UE and the moving direction of the UE, if the included angle is larger than the set value, the UE moves in the moving direction of the ith handover candidate cellConfirming the cell as a user pre-switching candidate cell; if it isThe cell is not taken as a pre-handover candidate cell; after secondary screening, a UE pre-switching candidate cell set can be obtained;

in step one, the UE continuously detects reference signal received power RSRP of the current service cell and the adjacent cell, and obtains the reference signal received power RSRP after smoothing by an exponential averaging filter^s(t), the filter model used is as follows:

RSRP^s(t)＝kRSRP^r(t-1)+(1-k)RSRP^r(t)

wherein, RSRP^s(t) denotes the filter output value, RSRP, at time t^r(t) denotes a reference signal received power received at time t, i.e., a filter input value, and k denotes a filter smoothing parameter;

the switching triggering condition is that the RSRP difference value after the adjacent cell and the current service cell are smoothed is higher than a triggering threshold value; if soRepresenting the smoothed RSRP of the current serving cell as the RSRP_i ^sRepresenting the smoothed RSRP of the ith adjacent cell, and the handover trigger condition is represented as: presence of i, satisfyWherein, RSRP_thIs a trigger threshold value;

in step three, the current serving cell notifies the pre-handover candidate cell to perform pre-handover preparation, which specifically includes:

1) the current service cell sends pre-switching preparation information to the pre-switching candidate cell;

2) the pre-switching candidate cell receives the pre-switching preparation message, executes resource reservation and sends a pre-switching preparation response message to the current serving cell;

3) the current service cell receives the pre-switching preparation response message and sends the pre-switching request response message to the UE;

in step five, the determining, by the current serving cell, a handover target cell according to the measurement report specifically includes:

1) current serving cell acquisition pre-handover candidate cell smoothed RSRP received at UE_i ^sAnd pre-switching candidate cell available bandwidth B_iI is more than or equal to 1 and less than or equal to N, wherein N is the number of pre-handover candidate cells;

2) the current service cell estimates the transmission rate after the UE is switched to the pre-switching candidate cell according to the information of the UE pre-switching candidate cell, and the transmission rate is R_iThe transmission rate after the UE is identified to be switched to the ith cell can be obtained

Wherein,the RSRP, N of the UE arrived at by the jth cell with the same frequency as the ith cell_iFor the number of cells of the same frequency as the ith cell, σ²Is the noise power; the current serving cell selects a pre-switching candidate cell with the maximum corresponding transmission rate as a switching target cell, namely: i.e. i^*＝argmaxR_i。