Synchronization apparatus and method in wireless network systems

1. A method for synchronizing receiving time of a node in a wireless network system node, the method comprising:

estimating propagation delays between the node and a plurality of neighbor nodes corresponding to one hop of the node; and

requesting at least one of a neighbor node having a minimum propagation delay and a neighbor node having a maximum propagation delay to change its signal transmission time.

2. The method of claim 1 , wherein the requesting of the at least one neighbor node comprises requesting the at least one neighbor node to change its signal transmission time when a difference between the maximum propagation delay and the minimum propagation delay is greater than the length of a cycle prefix (CP) of one symbol.

3. The method of claim 1 , wherein the requesting of the at least one neighbor node comprises requesting the neighbor node having the minimum propagation delay to delay its signal transmission time.

4. The method of claim 1 , wherein the requesting of the at least one neighbor node comprises requesting the neighbor node having the maximum propagation delay to advance its signal transmission time.

5. The method of claim 1 , wherein the requesting of the at least one neighbor node comprises requesting the neighbor node having the minimum propagation delay to delay its signal transmission time, and requesting the neighbor node having the maximum propagation delay to advance its signal transmission time.

6. The method of claim 1 , wherein the requesting of the at least one neighbor node comprises:

checking whether a fast Fourier transform (FFT) start point is present within a range between the maximum propagation delay and the minimum propagation delay;

excluding the at least one of a neighbor node having a minimum propagation delay and a neighbor node having a maximum propagation delay from among the plurality of neighbor nodes until the FFT start point is present within the range between the maximum propagation delay and the minimum propagation delay when the FFT start point is not present; and

requesting the excluded neighbor node to change its signal transmission time.

7. The method of claim 6 , wherein the requesting of the at least one neighbor node further comprises setting the FFT start point to a value closest to an FFT start reference point between the maximum propagation delay and the minimum propagation delay when the FFT start point is present within the range between the maximum propagation delay and the minimum propagation delay.

8. The method of claim 6 , wherein the requesting of the at least one neighbor node further comprises setting the FFT start point to the minimum propagation delay when the FFT start point is not present within the range between the maximum propagation delay and the minimum propagation delay.

9. The method of claim 1 , further comprising:

measuring the amount of interference for a predetermined time when the at least one neighbor node rejects the transmission time change request; and

forcibly instructing the at least one neighbor node to change its signal transmission time when the measured amount of interference exceeds a predetermined reference value.

10. The method of claim 1 , wherein the estimating of the propagation delays comprises calculating round trip delays between the specific node and the plurality of neighbor nodes through a ranging procedure with the plurality of neighbor nodes, and estimating the propagation delays from the round trip delays.

11. A method for synchronizing transmission time of a node in a wireless network system, the method comprising:

estimating propagation delays between the node and a plurality of neighbor nodes corresponding to one hop of the node; and

requesting at least one of a neighbor node having a minimum propagation delay and a neighbor node having a maximum propagation delay to change its signal receiving time.

12. The method of claim 11 , wherein the requesting of the at least one neighbor node comprises requesting the neighbor node having the minimum propagation delay to delay its signal receiving time, and requesting the neighbor node having the maximum propagation delay to advance its signal receiving time.

13. The method of claim 11 , wherein the requesting of the at least one neighbor node comprises:

checking whether a transmission start point is present within a range between the maximum propagation delay and the minimum propagation delay;

excluding at least one of a neighbor node having a minimum propagation delay and a neighbor node having a maximum propagation delay from among the plurality of neighbor nodes until the transmission start point is present within the range between the maximum propagation delay and the minimum propagation delay when the FFT start point is not present; and

requesting an excluded neighbor node to change its signal receiving time.

14. The method of claim 13 , wherein the requesting of the at least one neighbor node further comprises setting the transmission start point to a value closest to a transmission start reference point between the maximum propagation delay and the minimum propagation delay when the transmission start point is present within the range between the maximum propagation delay and the minimum propagation delay.

15. The method of claim 13 , wherein the requesting of the at least one neighbor node further comprises setting the transmission start point to the minimum propagation delay when the transmission start point is not present within the range between the maximum propagation delay and the minimum propagation delay.

16. An apparatus for synchronizing nodes in a wireless network system, the apparatus comprising:

a delay estimation unit configured to estimate propagation delays between the node and a plurality of neighbor nodes corresponding to one hop of the node;

a reception synchronization unit configured to request at least one of a neighbor node having a minimum propagation delay and a neighbor node having a maximum propagation delay to change its signal transmission time using the propagation delays of the plurality of neighbor nodes; and

a transmission synchronization unit configured to request at least one of a neighbor node having a minimum propagation delay and a neighbor node having a maximum propagation delay to change its signal receiving time using the propagation delays of the plurality of neighbor nodes.

17. The apparatus of claim 16 , wherein the reception synchronization unit excludes at least one of a neighbor node having a minimum propagation delay and a neighbor node having a maximum propagation delay until an FFT start point is present within the range between the maximum propagation delay and the minimum propagation delay when the FFT start point is not present within the range between the maximum propagation delay and the minimum propagation delay, and requests an excluded neighbor node to change its signal transmission time.

18. The apparatus of claim 17 , wherein the reception synchronization unit measures the amount of interference for a predetermined time when the at least one neighbor node rejects the transmission time change request, and forcibly instructs the at least one neighbor node to change its signal transmission time when the measured amount of interference exceeds a predetermined reference value.

19. The apparatus of claim 17 , wherein the reception synchronization unit sets the FFT start point to a value closest to a predetermined FFT start reference point between the maximum propagation delay and the minimum propagation delay when the FFT start point is present within the range between the maximum propagation delay and the minimum propagation delay, and sets the FFT start point to the minimum propagation delay when the FFT start point is not present within the range between the maximum propagation delay and the minimum propagation delay.

20. The apparatus of claim 16 , wherein the transmission synchronization unit excludes at least one of a neighbor node having a minimum propagation delay and a neighbor node having a maximum propagation delay until a transmission start point is present within the range between the maximum propagation delay and the minimum propagation delay when the transmission start point is not present within the range between the maximum propagation delay and the minimum propagation delay, and requests an excluded neighbor node to change its signal receiving time.