FEMTOCELL SEARCH METHOD FOR MACRO TO FEMTO HANDOVER

• US 20110105129A1
• Filed: 03/26/2009
• Published: 05/05/2011
• Est. Priority Date: 06/27/2008
• Status: Active Grant

• Current Assignee: Electronics and Telecommunications Research Institute, Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Lee, Hyun, Kim, Won-Ik, Lim, Kwang Jae, Chang, Sung Cheol, Yoon, Chul Sik, Jin, Sung-Geun
• Granted Patent: US 8,326,304 B2
• Time in Patent Office: Days
• US Class Current: 455/443
• CPC Class Codes: H04W 36/00835 Determination of neighbour cell lists
• CPC Class Codes: H04W 36/0085 Hand-off measurements

Abstract

The present invention relates to a femtocell search method for a handover from a macrocell to a femtocell. The present invention relates to a method for a terminal that accesses a macrocell to search a femtocell in an environment where a plurality of femtocells are overlapped in one macrocell. The terminal searches a femtocell by using a dummy preamble in order to minimize the size of neighbor cell lists broadcasted from the macrocell to the terminal. Therefore, according to the present invention, an MAC overhead can be minimized by eliminating neighbor femtocell lists in a mobile neighbor advertisement (MOB_NBR_ADV) message broadcasted from the macrocell, and the terminal can search a femtocell with a minimum scanning load by checking only a femtocell dummy preamble in a dedicated symbol of the macrocell.

Claims

1. A search method of a terminal for searching a second base station in an environment where a cell of a first base station and a plurality of cells of a plurality second base stations are overlapped, comprising:

checking dummy preamble information on the plurality of second base stations by receiving a message broadcasted from the first base station;

receiving a plurality of dummy preambles broadcasted from the plurality of second base stations through a predetermined dedicated symbol; and

measuring received signal strengths from the plurality of dummy preambles, and searching a candidate base station according to the measured result.

2. The search method of claim 1, wherein the message broadcasted from the first base station includes at lease one of information on the dedicated symbol, cell identifiers (IDs) of the plurality of cells generated by the plurality of second base stations, a frequency index, and a preamble index.

3. The search method of claim 1, wherein a cell ID and a received signal strength indication (RSSI) value of each of the plurality of second base stations that have broadcasted the plurality of dummy preambles are acquired from the plurality of dummy preambles.

4. The search method of claim 3, wherein the searching of the candidate base station comprises:

determining whether a dummy preamble having received signal strength that is greater than a predetermined reference value exists among the plurality of dummy preambles;

if a dummy preamble having the received signal strength that is greater than the reference value exists, requesting information on a second base station that has broadcasted the dummy preamble, from the first base station;

receiving the information from the first base station, and setting a second base station of dummy preambles each of which has received signal strength that is greater than a predetermined reference value to a candidate base station; and

searching the candidate base station.

5. The search method of claim 4, wherein the requesting of the information on the second base station from the first base station comprises generating a femtocell information request message that includes the cell ID acquired from the dummy preamble.

6. The search method of claim 4, wherein the setting of the candidate base station further comprises receiving a femtocell information response message that includes a neighbor femtocell list of a second base station that has broadcasted the dummy preamble of which received signal strength is greater than the reference value from the first base station.

7. A search method of a base station in an environment where a cell of a first base station and a plurality of cells of a plurality of second base stations are overlapped, comprising:

allocating a dedicated symbol to be used for broadcasting a dummy preamble to a terminal from the second base station;

broadcasting a message to the terminal, the message including at least one of cell IDs of the plurality of cells generated by the plurality of second base stations, a frequency index, and a preamble index;

receiving a femtocell information request message that includes a cell ID from the terminal that has received the dummy preamble broadcasted from the second base station; and

including a neighbor femtocell list that includes the cell ID among pre-stored neighbor femtocell lists in a femtocell information response message and transmitting the femtocell information response message to the terminal.

8. The search method of claim 7, wherein, in the allocating of the dedicated symbol, the second base station acquires information on the allocated dedicated symbol from the first base station and checks the information.

9. The search method of claim 8, wherein, when the first base station and the second base station use different frequencies, the search method further comprises:

the second base station performing frequency switching from an operation frequency used by the second base station to an operation frequency used by the first base station;

the second base station broadcasting a dummy preamble to the terminal through a dedicated symbol that is predetermined by the first base station; and

the second base station performing frequency switching from the operation frequency used by the first base station to the operation frequency used by the second base station.

10. The search method of claim 9, wherein, when two or more dedicated symbols are provided, the search method comprises:

the second base station collecting dedicated symbol information by receiving information on the dedicated symbols from the first base station;

the base station checking a received signal strength indication (RSSI) value of neighbor base stations when the two or more dedicated symbols are preoccupied by the neighbor base stations of the second base station; and

the base station sharing a dedicated symbol preoccupied by a neighbor base station having the lowest RSSI value based on the RSSI value to broadcast a dummy preamble to the terminal.

11. The search method of claim 10, wherein the first base station is a base station that forms a macrocell, and the second base station is a base station that forms a femtocell.