System and method for determining synchronization point in OFDM modems for accurate time of flight measurement

• US 20040252630A1
• Filed: 06/07/2004
• Published: 12/16/2004
• Est. Priority Date: 06/05/2003
• Status: Active Grant

• Current Assignee: ARRIS Enterprises LLC (CommScope Holding Company, Inc.)
• Original Assignee: MeshNetworks, Inc. (Motorola Solutions, Inc.)
• Inventors: Alapuranen, Pertti O.
• Granted Patent: US 7,116,632 B2
• Time in Patent Office: Days
• US Class Current: 370/208
• CPC Class Codes: H04L 27/2656 Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 40/24 Connectivity information management, e.g. connectivity discovery or connectivity update
• CPC Class Codes: H04W 56/0065 using measurement of signal travel time
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks
• CPC Class Codes: H04W 92/18 between terminal devices

Abstract

A system and method including an algorithm that can use the linear time shift property of the subcarrier modulation to provide accurate frame synchronization for communications between nodes in a wireless network, where nodes employ orthogonal frequency division multiplexing (OFDM) modems. The subcarrier modulation is typically performed with a Fast Fourier Transform (FFT) that includes a time shift between Inverse Fast Fourier Transform (IFFT) and guard interval insertion at transmission, but due to the guard insertion, the system and method of the present invention corrects the time shifts allowing accurate TOF calculations.

Claims

1. A method for determining a synchronization point in an orthogonal frequency division multiplexing (OFDM) modem of a node in a wireless communication network, the synchronization point being used for time of flight (TOF) measurements, the method comprising:

detecting receipt of a frame by the node; and

cross-correlating the time of receipt of the received frame with a stored waveform in the node to determine the synchronization point.

2. A method as claimed in claim 1, wherein:

the cross-correlating is performed to determine the synchronization point relative to a counter in the node.

3. A method as claimed in claim 1, wherein:

the node is a wireless node and the network is an ad-hoc multi-hopping peer-to-peer communication network.