Downlink signal configuring method and device in mobile communication system, and synchronization and cell searching method and device using the same

Abstract

Disclosed is a downlink signal configuring method and device, and synchronization and cell search method and device using the same in a mobile communication system. A downlink frame has plural symbols into which pilot subcarriers are distributively arranged with respect to time and frequency axes. Initial symbol synchronization and initial frequency synchronization are estimated by using a position at which autocorrelation of a cyclic prefix of a downlink signal and a valid symbol of the downlink is maximized, and cell search and integer-times frequency synchronization are estimated by using pilot subcarriers included in the estimated symbol. Fine symbol synchronization, fine frequency synchronization, and downlink frame synchronization is estimated by using an estimated cell search result. Downlink frequency and time tracking is performed, cell tracking is performed by using a position set of pilot subcarriers inserted into the downlink frame, fine symbol synchronization tracking and fine frequency synchronization tracking are repeated by using the pilot subcarriers to perform the frequency and time tracking of the downlink frame.

What is claimed is: 
     
       1. A method of configuring a downlink signal in an orthogonal frequency division multiplexing access-frequency division duplexing (OFDMA-FDD) mobile communication system, said method comprising:
 (a) configuring a downlink frame with a plurality of symbols; and 
 (b) for each symbol, allocating a plurality of traffic subcarriers and a plurality of pilot subcarriers, said pilot subcarriers being distributed with respect to both time and frequency, a part of said pilot subcarriers being reference for a mobile station to perform time synchronization, frequency synchronization, and cell search; 
 wherein 
 the pilot subcarriers are distributed at regular intervals with respect to time, and are distributed at irregular intervals with respect to frequency; 
 said system comprises a plurality of cells; 
 the pilot subcarriers are allocated to the cells according to proper position sets of pilot subcarriers so that the pilot subcarriers in adjacent cells are not superimposed; 
 when the number of cells is greater than an available number of the proper position sets, the pilot subcarriers are allocated so as to minimize a number of pilot subcarriers that are superimposed in non-adjacent cells; 
 the cells are divided into groups of cells; 
 a predetermined number of said pilot subcarriers are allocated for each cell, said predetermined number being generated by dividing the number of subcarriers by the number of cells; 
 as to insufficient pilot subcarriers, part of said pilot subcarriers being allocated for each cell are allocated to the cells which have the same position in different groups; and 
 the proper position set K ig+j  of pilot subcarriers allocated to each j th  cell of each i th  cell group is determined according to the following equations
   K={f K, 0 , f K, 1 , . . . , f K, gNp−1 } 
   h i (k)=v(k)+(ik)modg 
   K ig+j ={f K, r |r=kg+(h imodg (k)+j)modg} 
 
 where 
 g is a prime number that satisfies Nu/Np≥g; 
 Nu is the number of subcarriers; 
 Np is the number of subcarriers included in each cell group; 
 G is the number of cells in each cell group, wherein G<g; 
 K is a set of subcarriers f K,O , f K,1 , . . . f K,gNp−1  selected to be pilot subcarriers; 
 h imodg  is a default sequence allocated to the i th  cell group; 
 v(k) is a specified pseudo random sequence having values from 0 to (g−1); and 
 j is a valued from 0 to (G−1). 
 
     
     
       2. The method of  claim 1 , wherein the pilot subcarriers are not punctured at a position other than the position of subcarriers used for transmission to the mobile station, whereby the pilot subcarriers are not transmitted. 
     
     
       3. A communication method comprising:
 transmitting, at a first cell among a plurality of cells, a first frame, wherein the first frame comprises a first pilot sequence consisting of a plurality of elements, and positions of the elements of the first pilot sequence with respect to time and frequency within the first frame are determined at least based on a number representing the first cell; and   transmitting, at a second cell among the plurality of cells, a second frame, wherein the second frame comprises a second pilot sequence consisting of a plurality of elements, and positions of the elements of the second pilot sequence with respect to time and frequency within the second frame are determined at least based on a number representing the second cell,   wherein the plurality of cells are grouped into a plurality of cell groups and, if the first cell and the second cell belong to a same cell group, each of the positions of the elements of the first pilot sequence within the first frame is different from each of the positions of the elements of the second pilot sequence within the second frame.   
     
     
       4. The method of claim 3, wherein the first pilot sequence allows a terminal to estimate a first channel condition and the second pilot sequence allows the terminal to estimate a second channel condition, and wherein the terminal performs handover from the first cell to the second cell at least based on the estimated first channel condition and the second channel condition. 
     
     
       5. The method of claim 3, wherein the second cell is a neighboring cell to the first cell. 
     
     
       6. The method of claim 3, further comprising:
 transmitting, at a third cell among the plurality of cells, a third frame, wherein the third frame comprises a third pilot sequence consisting of a plurality of elements, and positions of the elements of the third pilot sequence with respect to time and frequency within the third frame are determined at least based on a number representing the third cell; and   wherein some of the positions of the elements of the first pilot sequence within the first frame are same as some of the positions of the elements of the third pilot sequence within the third frame.   
     
     
       7. The method of claim 3, wherein the pilot sequence is derived from a pseudo random sequence. 
     
     
       8. A communication method, comprising:
 receiving, at a user equipment (UE), a first frame from a first cell among a plurality of cells, wherein the first frame comprises a first pilot sequence consisting of a plurality of elements, and positions of the elements of the first pilot sequence with respect to time and frequency within the first frame are determined at least based on a number representing the first cell;   receiving, at the UE, a second frame from a second cell among the plurality of cells, wherein the second frame comprises a second pilot sequence consisting of a plurality of elements, and positions of the elements of the second pilot sequence with respect to time and frequency within the second frame are determined at least based on a number representing the second cell;   estimating, at the UE, a first channel condition based on the first pilot sequence; and   estimating, at the UE, a second channel condition based on the second pilot sequence,   wherein the plurality of cells are grouped into a plurality of cell groups and, if the first cell and the second cell belong to a same cell group, each of the positions of the elements of the first pilot sequence within the first frame is different from each of the positions of the elements of the second pilot sequence within the second frame.   
     
     
       9. The method of claim 8, further comprising performing handover from the first cell to the second cell, wherein the handover is at least based on the estimated first channel condition and the second channel condition. 
     
     
       10. The method of claim 8, wherein:
 the second cell is a neighboring cell to the first cell.   
     
     
       11. The method of claim 8, further comprising:
 receiving, at the user equipment, a third frame from a third cell among the plurality of cells, wherein the third frame comprises a third pilot sequence consisting of a plurality of elements, and positions of the elements of the third pilot sequence with respect to time and frequency within the third frame are determined at least based on a number representing the third cell;   and wherein some of the positions of the elements of the first pilot sequence within the first frame are same as some of the positions of the elements of the third pilot sequence within the third frame.   
     
     
       12. An apparatus for wireless communication, comprising:
 a memory; and   a processor operably coupled to the memory, wherein the processor, when executing program instructions stored in the memory, is configured to:   cause the apparatus to receive a first frame from a first cell among a plurality of cells, wherein the first frame comprises a first pilot sequence consisting of a plurality of elements, and positions of the elements of the first pilot sequence with respect to time and frequency within the first frame are determined at least based on a number representing the first cell;   cause the apparatus to receive a second frame from a second cell among the plurality of cells, wherein the second frame comprises a second pilot sequence consisting of a plurality of elements, and positions of the elements of the second pilot sequence with respect to time and frequency within the second frame are determined at least based on a number representing the second cell;   estimate a first channel condition based on the first pilot sequence; and   estimate a second channel condition based on the second pilot sequence,   wherein the plurality of cells are grouped into a plurality of cell groups and, if the first cell and the second cell belong to a same cell group, each of the positions of the elements of the first pilot sequence within the first frame is different from each of the positions of the elements of the second pilot sequence within the second frame.   
     
     
       13. The apparatus of claim 12, wherein the processor is further configured to:
 cause the apparatus to perform handover from the first cell to the second cell, wherein the handover is at least based on the estimated first channel condition and the second channel condition.   
     
     
       14. The apparatus of claim 12, wherein:
 the second cell is a neighboring cell to the first cell.   
     
     
       15. The apparatus of claim 12, wherein the processor is further configured to:
 cause the apparatus to receive a third frame from a third cell among the plurality of cells, wherein the third frame comprises a third pilot sequence consisting of a plurality elements, and   
       positions of the elements of the third pilot sequence with respect to time and frequency within the third frame are determined at least based on a number representing the third cell;
 and wherein some of the positions of the elements of the pilot sequence within the first frame are same as some of the positions of the elements of the third pilot sequence within the third frame. 
 
     
     
       16. A device for a wireless communication system, the device comprising:
 a memory; and   a processor operably coupled to the memory,   wherein the processor, when executing program instructions stored in the memory, is configured to:   cause a first frame to be transmitted from a first cell among a plurality of cells, wherein the first frame comprises a first pilot sequence consisting of a plurality of elements, and   
       positions of the elements of the first pilot sequence with respect to time and frequency within the first frame are determined at least based on a number representing the first cell; and
 cause a second frame to be transmitted from a second cell among the plurality of cells, wherein the second frame comprises a second pilot sequence consisting of a plurality of elements, and positions of the elements of the second pilot sequence with respect to time and frequency within the second frame are determined at least based on a number representing the second cell, 
 wherein the plurality of cells are grouped into a plurality of cell groups and, if the first cell and the second cell belong to a same cell group, each of the positions of the elements of the first pilot sequence within the first frame is different from each of the positions of the elements of the second pilot sequence within the second frame. 
 
     
     
       17. The device of claim 16, wherein the first pilot sequence allows a terminal to estimate a first channel condition and the second pilot sequence allows the terminal to estimate a second channel condition, and wherein the terminal performs handover from the first cell to the second cell at least based on the estimated first channel condition and the second channel condition. 
     
     
       18. The device of claim 16, wherein the second cell is a neighboring cell to the first cell. 
     
     
       19. The device of claim 16, wherein the processor is further configured to:
 cause a third cell among the plurality of cells a third frame, wherein the third frame comprises a third pilot sequence consisting of a plurality of elements, and positions of the elements of the third pilot sequence with respect to time and frequency within the third frame are determined at least based on a number representing the third cell;   and wherein some of the positions of the elements of the pilot sequence within the first frame are same as some of the positions of the elements of the third pilot sequence within the third frame.   
     
     
       20. The device of claim 16, wherein the pilot sequence is derived from a pseudo random sequence. 
     
     
       21. An apparatus for a user equipment (UE), the apparatus comprising:
 a memory; and   a processor operably coupled to the memory, wherein the processor, when executing program instructions stored in the memory, is configured to:   cause the UE to receive a first frame from a first cell among a plurality of cells, wherein the first frame comprises a first pilot sequence consisting of a plurality of elements, and positions of the elements of the first pilot sequence with respect to time and frequency within the first frame are determined at least based on a number representing the first cell,   cause the UE to receive a second frame from a second cell among the plurality of cells, wherein the second frame comprises a second pilot sequence consisting of a plurality of elements, and positions of the elements of the second pilot sequence with respect to time and frequency within the second frame are determined at least based on a number representing the second cell;   estimate a first channel condition based on the first pilot sequence; and   estimate a second channel condition based on the second pilot sequence,   wherein the plurality of cells are grouped into a plurality of cell groups and, if the first cell and the second cell belong to a same cell group, each of the positions of the elements of the first pilot sequence within the first frame is different from each of the positions of the elements of the second pilot sequence within the second frame.   
     
     
       22. The apparatus of claim 21, wherein the processor is further configured to:
 cause the UE to perform handover from the first cell to the second cell, wherein the handover is at least based on the estimated first channel condition and the second channel condition.   
     
     
       23. The apparatus of claim 21, wherein:
 the second cell is a neighboring cell to the first cell.   
     
     
       24. The apparatus of claim 21, wherein the processor is further configured to:
 cause the UE to receive a third frame from a third cell among the plurality of cells, wherein the third frame comprises a third pilot sequence consisting of a plurality elements, and positions of the elements of the third pilot sequence with respect to time and frequency within the third frame are determined at least based on a number representing the third cell;   and wherein some of the positions of the elements of the pilot sequence within the first frame are same as some of the positions of the elements of the third pilot sequence within the third frame.