SYNCHRONIZATION OF DISTRIBUTED NETWORKS

• US 20090041003A1
• Filed: 02/21/2007
• Published: 02/12/2009
• Est. Priority Date: 02/23/2006
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Cordeiro, Carlos M., Challapali, Kiran S.
• Granted Patent: US 8,284,755 B2
• Time in Patent Office: Days
• US Class Current: 370/350
• CPC Class Codes: H04B 7/2696 Over the air autonomous synchronisation, e.g. by monitoring network activity H04B7/2693 takes precedence
• CPC Class Codes: H04J 3/0679 by determining clock distribution path in a network

Abstract

A system (400), apparatus (300), and method (100) are provided to synchronize distributed (otherwise uncoordinated) networks (400) of independent nodes (401_i). Such synchronization can be used in a number of different ways. In the context of cognitive radios, such synchronization can be used to synchronize quiet periods. Quiet periods are times when all cognitive radios (that are otherwise uncoordinated) become quiet so that incumbent users can be detected reliably. The technique of the present invention converges quickly and scales well.

Claims

1. A synchronization system (400) for wireless networks, comprising:

a plurality of uncoordinated wireless devices j (401_j) configured to transmit a beacon (20j.2.1) in a beacon period (20j.2) having a beacon period start time BPST_j (20j.1) and receive a beacon (20i.2.1) in a beacon period (20i.2) having a beacon period start time BPST_i (20i.1) for all devices i (401_i)≠

j (401_j); and

a beacon alignment apparatus (300) that aligns the BPST_j of device j such that BPST_j (20j.1)=BPST_i (20i.1) for all devices j≠

i,

wherein the beacon alignment apparatus (300) is used by each device j whenever the device j receives a beacon (20i.2.1) from another device i of said plurality and BPST_j (20j.1)≠

BPST_i (20i.1).

2. The system of claim 1, wherein the beacon period (20i.220j.2) occurs at a beginning of a superframe (20i 20j).

3. The system of claim 1, wherein each device (401_i) of said plurality is further configured to include an own beacon alignment apparatus (300).

4. The system of claim 3, wherein the beacon alignment apparatus (300) is configured to include a synchronizer module (303) to perform a pre-determined adjustment method (100) until one of the conditions holds selected from the group consisting of the algorithm has been performed a pre-specified number of times and BPST_j ε

1^st half of BPST_i (20i.1) and then respectively set BPST_j (20j.1) to a random number and to BPST_i (20i.1).

5. The system of claim 4, wherein the beacon period (20i.220j.2) occurs at a beginning of a superframe (20i 20j).

6. The system of claim 1, wherein the beacon alignment apparatus (300) is configured to include a synchronizer module (303) to perform a pre-determined adjustment method (100) until one of the conditions holds selected from the group consisting of the algorithm has been performed a pre-specified number of times and BPST_j (20j.1) ε

1^st half of BPST_i (20i.1) and then respectively set BPST_j (20j.1) to a random number and to BPST_i (20i.1).

7. The system of claim 6, wherein the beacon period (20i.220j.2) occurs at a beginning of a superframe (20i 20j).

8. A beacon alignment apparatus (300), comprising:

an antenna (305) to transmit an own beacon (304 20j.2.1) in a beacon period (20j.2) having a beacon period start time BPST_j (20j.1) and receive a beacon (301 20i.2.1) of another wireless device i (401_i) said received beacon (301 20i.2.1) being received in a beacon period (20i.2) having a beacon period start time BPST_i (20i.1);

a synchronization memory (302) to store said received beacon (301 20i.2.1) and a synchronization counter for said received beacon (301 20i.2.1);

a synchronizer module (303) operably connected to said antenna (305) to accept said received beacon (301 20i.2.1) therefrom and operably connected to said synchronization memory (302) to store said accepted received beacon (301 20i.2.1) therein and, using said synchronization counter (302), perform a pre-determined adjustment method (100) with respect to said own beacon (304 20j.2.1).

9. The apparatus (300) of claim 8, wherein the beacon period (20i.220j.2) occurs at a beginning of a superframe (20i 20j).

10. The apparatus (300) of claim 8, wherein:

the synchronization counter is set to a pre-determined number of times to perform the pre-determined adjustment method (100); and

the pre-determined adjustment method comprises iteration until one of the conditions holds selected from the group consisting of iteration has been performed the pre-determined number of times and BPST_j ε

1^st half of BPST_i (20i1) and then respectively setting BPST_j (20j.1) to a random number and to BPST_i (20i.1).

11. The apparatus (300) of claim 10, wherein the beacon period (20i.220j.2) occurs at a beginning of a superframe (20i 20j).

12. A method (100) for synchronizing a plurality of uncoordinated wireless devices, comprising the steps of:

receiving a beacon (20i.2.1) in a beacon period (20i.2) having a beacon period start time BPST_i (20i. 1) from an uncoordinated wireless device i by another uncoordinated wireless device j that transmits an own beacon (20j.2.1) in a beacon period (20j.2) having a beacon period start time BPST_j (20j.1) where j≠

i;

if an adjustment procedure (100) has been performed by the device j for the uncoordinated device i a predetermined number of times (104), setting (105) the beacon period start time BPST_j for the device j to a random number, otherwise if BPST_j ε

1^st half of BPST_i (20i.1) setting (108) BPST_j to BPST_i(20i.1); and

transmitting an own beacon by device j (20j.2.1) in the beacon period (20j.2) having the beacon period start time BPST_j (20j.1).

13. The method of claim 13, wherein the beacon period (20i.220j.2) occurs at a beginning of a superframe (20i 20j).