US 5,408,506 A · Distributed time synchronization system and method

Abstract

A distributed time synchronization system and method synchronizes nodes within a frequency hopping spread spectrum (FHSS) local area network (LAN) group to a virtual master clock value. Each node system of the present invention comprises a CPU, an input device, a display device, a printer or hard copy device, a given amount of RAM and ROM memory, a data storage device, a local clock, a transmitter/receiver, an antenna, a virtual master clock processor, and a common data bus. The method of the present invention comprises the inclusion of a node's local clock value in a message just prior to transmission over the network, storage of a node's local clock value in RAM after an incoming message has been received, and the calculation of the time delay between the sending node and the receiving node by the virtual master clock processor. The virtual master clock processor utilizes this time delay in maintaining a virtual master clock value, which it uses in adjusting the value of the node's local clock at periodic intervals. This synchronizes the receiving node to the virtual master clock value. If the magnitude of the time delay exceeds a maximum allowed value, the magnitude is clamped to the maximum allowed value, thereby maintaining synchronization within a predetermined tolerance. A node can receive a message transmitted over the FHSS LAN regardless of the message address. Synchronization is therefore maintained without requiring a node to be able to communicate with any specific node within the FHSS LAN group.

Claims19

Dependent claims

A distributed time synchronization system for a wireless communications network having a plurality of node systems, each node system comprising:

a display device for displaying information to the user, the display device having an input;
an input device for inputting information to the system, the input device having an output;
a local clock having an input and an output for providing a timing signal, the input of the local clock for receiving a signal to adjust the local clock;
a transmitter/receiver for receiving and translating radio signals into digital signals and for translating and transmitting digital signals into radio signals in response to digital control signals, the transmitter/receiver coupled to an antenna to receive and transmit radio signals, the transmitter/receiver having an input and an output for processing digital signals;
a virtual master clock processing means for calculating the value of a virtual master clock for the node system, the virtual master clock processing means coupled to the transmitter/receiver, the virtual master clock processing means extracting time synchronization information from each message received over the network during a predetermined time interval and using the synchronization information extracted from each message received to calculate the value of the virtual master clock;
a processing unit for adding synchronization information to each message sent by the transmitter/receiver, and for using the value of the virtual master clock to adjust the local clock, the processing unit having inputs and outputs coupled to the input device, the display device, the local clock, the transmitter/receiver and the virtual master clock processing means;
and
a memory for storing data and routines, the memory having inputs and outputs, the memory including a first memory area storing a routine for sending messages with time synchronization information, a second memory area storing a routine for receiving messages and storing a local clock value corresponding to each message received, and a third memory area storing a routine for adjusting the local clock using extracted synchronization information, the first and second memory areas coupled to the transmitter/receiver and the processing unit, and the third memory area coupled to the local clock and the virtual master clock processing means.

5 more elements

A computer implemented method for synchronizing a plurality of node computer systems in a communications network, the node computer systems being coupled by a media, each node computer system having a local clock, the method comprising the steps of:

storing time synchronization information as part of a first message at a first node computer system;
sending the first message over the network using the first node computer system;
storing time synchronization information as part of a second message at a second node computer system;
sending the second message over the network using the second node computer system;
receiving the first message at a third node computer system in the communications network;
extracting the time synchronization information from the first message at the third node computer system;
receiving the second message at the third node computer system in the communications network;
extracting the time synchronization information from the second message at the third node computer system;
and
adjusting the local clock of the third node computer system using the time synchronization information extracted from both the first and second messages.

7 more elements

A computer implemented method for receiving messages and synchronizing a first node computer system in a communications network having a plurality of node computer systems being coupled by a media, the first node computer system having a local clock and a memory, the method comprising the steps of:

monitoring the media for a message;
determining whether a message was detected on the media;
returning to the monitoring step if a message was not detected on the media;
transferring the incoming message from a transmitter/receiver of the first node computer system to the memory of the first node computer system;
storing the value of a local clock of the first node computer system at the time the message is received in memory of the first node computer system;
extracting time synchronization information from each message received at the first node computer system;
and
adjusting the local clock of the first node computer system using the time synchronization information extracted from each message received.

5 more elements

Dependencies are inferred from the claim text.

Distributed time synchronization system and method

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Distributed time synchronization system and method

Life of this patent

Abstract

Claims19