Method for performing high-speed handover in base station cooperative wireless communication system, and device for same

Abstract

Disclosed in the present application is a method for a terminal to perform a handover in a wireless communication system. In particular, the method comprises the steps of: receiving a random access triggering signal from a serving cell; executing a random access procedure with a target cell on the basis of the random access triggering signal; receiving a downlink signal from the serving cell and transmitting an uplink signal to the target cell; receiving, from the serving cell, a message ordering a handover to the target cell; and transmitting, to the target cell, a predetermined message indicating the completed handover, on the basis of the message ordering a handover.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application may indicate which TA value or power control value is maintained through the handover command.

When the UE operates to directly receive a control channel of the target cell without using the random access procedure after handover as in the present invention, if a valid control channel signal is not received from the target cell for a predetermined time, the UE determines that handover has failed and receives the control channel from an original serving cell.

Hereinafter, additional information transmitted to the UE in a handover situation in which the above described random access procedure is omitted will be described in more detail. The additional information may be included in a handover command.

The additional information may include a C-RNTI which is to be used by the UE after handover to a target cell. To aid in a C-RNTI transfer operation, the macro eNB and the pico eNB may exchange a handover preparation signal through a backhaul link. For example, the macro eNB, which is a serving cell, may inform the pico eNB of an ID of a UE which is to perform handover to the pico eNB. Especially, the macro eNB may inform the pico eNB that a corresponding UE is performing a CoMP operation in the pico eNB and simultaneously may request a C-RNTI to be used by the UE after handover. As a response to a C-RNTI request, the pico eNB may inform the macro eNB of information about the C-RNTI to be used by the UE. Alternatively, the macro eNB, which is a serving cell, transmits a temporary C-RNTI to be used by the UE in the pico eNB, which is a target cell, to the UE and the UE transmits a prescribed message masked with the temporary C-RNTI to the target cell based on a timing and a resource indicated by the handover command. The prescribed message transmitted using the temporary C-RNTI may have the same format as a format (i.e. message 3 of FIG. 9) transmitted using a temporary C-RNTI in an existing random access procedure.

The additional information may also include scheduling request configuration information to be used by the UE after handover to the target cell. Instead of performing the random access procedure with respect to the target cell, the UE may transmit a scheduling request message to the target cell by using the scheduling request configuration information and transmit, as a response to the scheduling request message, information thereof and a message indicating that handover has been completed to the target cell by using a resource allocated by the target cell. Especially, upon receiving the handover command, the UE may be defined to transmit the scheduling request message using the scheduling request configuration information within a predetermined time. This is because the target cell will transmit a control channel after the UE transmits the scheduling request message since the scheduling request message may be interpreted as completion of handover of the UE (i.e. change of a cell receiving a DL control channel) although the UE should be capable of receiving the control channel from the target cell from a timing at which the scheduling request message is transmitted.

Meanwhile, such a handover scheme omitting the random access procedure may be applied even to a replacement process of a primary component carrier (or a primary cell (PCell)) in a wireless communication system to which carrier aggregation is applied. That is, in a process in which a secondary component carrier (or a secondary cell (SCell)) is reconfigured as the primary component carrier, since a UL transmission timing to the secondary component carrier has already been acquired and the replacement process of the primary component carrier conforms to a handover process, the handover scheme of the present can be applied.

FIG. 11 is a flowchart illustrating an example of performing a handover process by a UE according to an embodiment of the present invention. Especially, FIG. 11 illustrates the case in which the UE transmits a scheduling request message indicating that handover has been completed.

Referring to FIG. 11, in step 1100, the UE may receive a DL signal from a macro eNB and simultaneously transmit a UL signal to the macro eNB as illustrated in FIG. 8. Namely, step 1100 may correspond to a process before a CoMP scheme is applied.

Next, when the UE moves towards a pico eNB, the UE may perform a random access procedure for UL synchronization acquisition with the pico eNB in step 1105 according to a PDCCH received from the macro eNB. After UL synchronization acquisition, the UE operates in CoMP mode to receive the DL signal from the macro eNB and simultaneously transmit a UL signal to the pico eNB in step 1110 (refer to FIG. 9).

If the UE further moves toward the pico eNB (refer to FIG. 10), the UE may receive, from the macro eNB, a handover command message indicating that handover to the pico eNB should be performed in step 1115. The handover command message is desirably a high-speed handover message according to the present invention.

As described above, the high-speed handover command message may include scheduling request configuration information to be used after handover. Upon receiving the high-speed handover message, the UE may immediately transmit a scheduling request message to the pico eNB without an additional random access procedure.

Accordingly, the UE may transmit the scheduling request message to the target cell using the scheduling request configuration information in step 1120. Especially, the UE, which has received the handover command, needs to transmit the scheduling request message using the scheduling request configuration information within a predetermined time. In addition, as described above, the UE may receive a DL control channel from the pico eNB, which is the target cell, from a timing at which the scheduling request message is transmitted.

FIG. 12 is a block diagram illustrating a communication device according to an embodiment of the present invention.

Referring to FIG. 12, a communication device 1200 includes a processor 1210, a memory 1220, a radio frequency (RF) module 1230, a display module 1240, and a user interface module 1250.

The communication device 1200 is illustrated for convenience of description and some modules may be omitted. The communication device 1200 may further include necessary modules. Some modules of the communication device 1200 may be further divided into sub-modules. The processor 1210 is configured to perform operations according to the embodiments of the present invention exemplarily described with reference to the drawings. Specifically, for a detailed description of operations of the processor 1210, reference may be made to the statements described with reference to FIGS. 1 to 11.

The memory 1220 is connected to the processor 1210 and stores operating systems, applications, program code, data, and the like. The RF module 1230 is connected to the processor 1210 and performs a function of converting a baseband signal into a radio signal or converting a radio signal into a baseband signal. For this, the RF module 1230 performs analog conversion, amplification, filtering, and frequency upconversion or performs inverse processes thereof. The display module 1240 is connected to the processor 1210 and displays various types of information. The display module 1240 may include, but is not limited to, a well-known element such as a liquid crystal display (LCD), a light emitting diode (LED), or an organic light emitting diode (OLED). The user interface module 1250 is connected to the processor 1210 and may include a combination of well-known user interfaces such as a keypad and a touchscreen.

The above-described embodiments are combinations of elements and features of the present invention in a predetermined manner. Each of the elements or features may be considered selective unless mentioned otherwise. Each element or feature may be practiced without being combined with other elements or features. Further, an embodiment of the present invention may be constructed by combining parts of the elements and/or features. Operation orders described in embodiments of the present invention may be rearranged. Some constructions of any one embodiment may be included in another embodiment and may be replaced with corresponding constructions of another embodiment. In the appended claims, claims that are not explicitly dependent on each other may of course be combined to provide an embodiment or new claims can be added through amendment after the application is filed.

The embodiments according to the present invention can be implemented by various means, for example, hardware, firmware, software, or combinations thereof. In the case of a hardware configuration, the embodiments of the present invention may be implemented by one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, etc.

In the case of a firmware or software configuration, an embodiment of the present invention may be implemented by a module, a procedure, or a function, which performs functions or operations described above. For example, software code may be stored in a memory unit and then may be executed by a processor. The memory unit may be located inside or outside the processor to transmit and receive data to and from the processor through various well-known means.

The present invention may be carried out in other specific ways than those set forth herein without departing from the spirit and essential characteristics of the present invention. The above embodiments are therefore to be construed in all aspects as illustrative and not restrictive. The scope of the invention should be determined by the appended claims and their legal equivalents and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

While a method for performing high-speed handover in an eNB-coordinated wireless communication system and an apparatus therefor have been described in the context of a 3GPP LTE system, the present invention is also applicable to many other wireless communication systems in addition to the 3GPP LTE system.

Claims

1. A method for performing handover by a user equipment (UE) in a wireless communication system, the method comprising:

receiving a random access triggering signal from a serving cell;

performing a random access procedure with a target cell based on the random access triggering signal;

receiving a downlink signal from the serving cell and transmitting an uplink signal to the target cell;

receiving, by the UE from a serving base station (bs), a handover command message indicating which commands the UE to perform handover to the a target cell from the serving cell bs, the handover command message including first information indicating whether a random access procedure to the target bs is to be skipped;

performing, by the UE, the handover to the target bs without performing the random access procedure to the target bs, based on that the first information indicates the random access procedure to the target bs is to be skipped; and

transmittinga prescribed, by the UE to the target bs based on a specific timing advance (ta), an uplink signal including a handover completion message indicating completion of that the handover to the target cell based on the handover command message bs is completed at the UE,

wherein the handover command message includes second information regarding a ta, based on that the first information indicates the random access procedure to the target bs is to be skipped,

wherein the UE obtains the specific ta from the second information regarding the ta in the handover command message based on that the first information indicates the random access procedure is to be skipped,

wherein the specific ta is a ta which has been used by the UE prior to the handover to the target bs and the second information indicates that the specific ta is to be reused for the target bs after the handover to the target bs, and

wherein the handover command message includes third information about a cell-radio network temporary identity (C-RNTI) to be used by the UE in the target bs.

2. The method according to claim 1, wherein the handover command message includes information indicating that the random access procedure is omitted.

3. The method according to claim 2, wherein the handover command message includes information about a temporary user equipment identity to be used by the user equipment in the target cell.

4. The method according to claim 2 1, wherein the handover command message includes information used for transmitting a scheduling request message by the user equipment UE to the target cell bs.

5. The method according to claim 1, wherein the serving cell is a macro base station and the target cell is a pico base station bs and the target bs are different eNodeBs (eNBs) in the wireless communication system.

6. The method according to claim 1, wherein the serving cell is a primary component carrier and the target cell is a secondary component carrier.

7. The method according to claim 6, wherein the secondary component carrier is reconfigured as the primary component carrier after the prescribed message is transmitted.

8. The method according to claim 1, wherein the prescribed handover completion message is related to a scheduling request message.

9. The method according to claim 1, wherein the a random access triggering signal is received through a physical control channel from the serving cell bs.

10. The method according to claim 1, further comprising:

receiving a downlink signal from the target cell bs; and

transmitting an another uplink signal to the target cell bs, after transmitting the prescribed uplink signal including the handover completion message,

wherein a power control process of the user equipment UE is maintained before and after the prescribed handover completion message is transmitted.

11. The method according to claim 1, further comprising:

monitoring, by the UE, a control channel signal of the target bs based on the C-RNTI included in the handover command message.

12. The method according to claim 11, wherein the uplink signal transmission is performed based on the control channel signal of the target bs.

13. The method according to claim 1, wherein the uplink signal transmission is performed based on the C-RNTI included in the handover command message.

14. The method according to claim 1, wherein the handover command message includes fourth information regarding an uplink resource allocated to the UE for transmission of the uplink signal to the target bs.

15. The method according to claim 1, further comprising:

determining whether the handover to the target bs is successful or failed based on whether a control channel signal of the target bs is received within a predetermined time duration.

16. A non-transitory medium readable by a processor and recorded thereon one or more instructions that cause the processor to perform operations including:

a reception procedure of a handover command message from a serving base station (bs), wherein the handover command message commands the processor to perform handover to a target bs, and the handover command message includes first information indicating whether a random access procedure to the target bs is to be skipped, second information regarding a timing advance (ta) based on that the first information indicates the random access procedure to the target bs is to be skipped, and third information about a cell-radio network temporary identity (C-RNTI) to be used by the processor in the target bs;

obtaining a specific ta from the second information regarding the ta in the handover command message based on that the first information indicates the random access procedure is to be skipped, wherein the specific ta is a ta which has been used by the processor prior to the handover to the target bs and the second information indicates that the specific ta is to be reused for the target bs after the handover to the target bs;

performing the handover to the target bs without performing the random access procedure to the target bs, based on that the first information indicates the random access procedure to the target bs is to be skipped; and

a transmission procedure of an uplink signal to the target bs based on the specific ta, the uplink signal including a handover completion message indicating that the handover to the target bs is completed at the processor.

17. A device for wireless communication, comprising:

a radio frequency (rf) module; and

a processor controlling the rf module:

to receive, from a serving base station (bs), a handover command message which commands the device to perform handover to a target bs, the handover command message including first information indicating whether a random access procedure to the target bs is to be skipped,

to perform the handover to the target bs without performing the random access procedure to the target bs, based on that the first information indicates the random access procedure to the target bs is to be skipped, and

to transmit, to the target bs based on a specific timing advance (ta), an uplink signal including a handover completion message indicating that the handover to the target bs is completed at the device,

wherein the handover command message includes second information regarding a ta, based on that the first information indicates the random access procedure to the target bs is to be skipped,

wherein the processor obtains the specific ta from the second information regarding the ta in the handover command message based on that the first information indicates the random access procedure is to be skipped,

wherein the specific ta is a ta which has been used by the device prior to the handover to the target bs and the second information indicates that the specific ta is to be reused for the target bs after the handover to the target bs, and

wherein the handover command message includes third information about a cell-radio network temporary identity (C-RNTI) to be used by the device in the target bs.