Method for controlling power of RRH in cloud RAN environment

1. A method for controlling power of a Remote Radio Head (RRH) by a Base Band Unit (BBU) in a Cloud Radio Access Network (C-RAN) environment having the BBU and the RRH separated from each other, the method comprising:

receiving, from a terminal, a measurement report message for reporting that a measured strength of a downlink (DL) signal of the RRH having a switched-off state is greater than or equal to a threshold,

wherein the RRH is controlled by the BBU associated with the RRH, and

wherein the BBU performs layer processing for the RRH;

transmitting, to the terminal, Radio Access Technology (RAT) information indicating RATs supported by the RRH in response to the measurement report message;

receiving, from the terminal, a wake-up request message containing information about a RAT preferred by the terminal among the RATs indicated by the RAT information; and

setting a power status of the RRH to Switch On based on the wake-up request message.

2. The method according to claim 1 , wherein the RAT information is acquired from an entity managing information about a mapping relationship between RRHs and BBUs or the RRH.

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

checking the power status of the RRH before transmitting the RAT information to the terminal,

wherein the power status is Switch On or Switch Off, and is checked from an entity managing information about a mapping relationship between RRHs and BBUs or the RRH.

4. The method according to claim 1 , wherein the RAT information expresses information about the RATs or a frequency band supported by the RRH as a bitmap, a combination of preconfigured bits for the respective RATs, or an Absolute Radio Frequency Channel Number (ARFCN) value.

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

acquiring information about a first BBU mapped to the RRH after receiving the wake-up request message,

wherein the information about the first BBU is acquired from an entity managing information about a mapping relationship between RRHs and BBUs.

6. The method according to claim 5 , further comprising:

changing, after the acquiring, a mapping relationship between the RRH and the first BBU to a mapping relationship between the RRH and a second BBU supporting the RAT preferred by the terminal.

7. The method according to claim 6 , wherein the changing comprises:

requesting that the entity configure a BBU supporting the RAT preferred by the terminal;

requesting that the second BBU establish connection to the RRH, based on a response for designation of the second BBU from the entity; and

receiving, from the second BBU, a response message indicating that connection to the RRH has been established.

8. The method according to claim 6 , wherein the changing comprises:

requesting that the entity configure a BBU supporting the RAT preferred by the terminal; and

receiving, from the first BBU, a response message indicating that connection between the second BBU and the RRH has been established when a procedure of coordination between the first BBU and the second BBU is completed according to an instruction from the entity.

9. The method according to claim 6 , wherein the changing comprises:

requesting that the entity configure a BBU supporting the RAT preferred by the terminal; and

receiving, from the entity, a response message indicating that connection between the second BBU and the RRH has been established when a procedure of coordination between the entity and the second BBU is completed.

10. The method according to claim 6 , wherein the changing comprises:

requesting that the first BBU configure a BBU supporting the RAT preferred by the terminal; and

receiving, from the first BBU, a response message indicating that connection between the second BBU and the RRH has been established when a procedure of coordination among the first BBU, the second BBU and the entity is completed according to a request from the first BBU.

11. A method for controlling power of a Remote Radio Head (RRH) by a Base Band Unit (BBU) in a Cloud Radio Access Network (C-RAN) environment having the BBU and the RRH separated from each other, the method comprising:

determining to set a power status of a first RRH having a switched-on state to Switch Off based on a measurement report message about the first RRH received from a terminal;

transmitting, to BBUs connected to the first RRH, an RRH status change request message for signaling that the power status of the first RRH should be set to Switch Off;

transmitting, when RRH status change response messages for approving the RRH status change request are received from all the BBUs connected to the first RRH, and RRH status change command message for instructing RRH switching to the BBUs;

performing, when RRH switching of the BBUs is completed, RRH switching for changing a mapping relationship with the first RRH to a mapping relationship with a second RRH; and

setting the power status of the first RRH to Switch Off,

wherein the first RRH and the second RRH are controlled by the BBU, and

wherein the BBU performs layer processing for the first RRH and the second RRH.

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

stopping, when an RRH status change failure message for rejecting the RRH status change request is received from at least one of the BBUs connected to the first RRH, a procedure of controlling the power of the RRH.

13. The method according to claim 11 , wherein the RRH status change command message comprises an indicator for designating one of the BBUs connected to the first RRH as a common BBU,

wherein the common BBU is a BBU connected to the first RRH to perform communication even if the first RRH is switched off.

14. The method according to claim 11 , wherein the performing of the RRH switching comprises:

determining completion of the RRH switching as an RRH status change command acknowledgement (ACK) message is received from the BBU in response to the RRH status change command message.

15. The method according to claim 11 , wherein the setting comprises:

switching off at least one of a transmission mode and reception mode of the first RRH and switching off a part or entirety of carriers and Radio Access Technologies (RATs) supported by the first RRH.