Pulse or digital communications – Spread spectrum – Frequency hopping
Reexamination Certificate
1995-04-06
2002-10-15
Luther, William (Department: 2664)
Pulse or digital communications
Spread spectrum
Frequency hopping
C375S356000
Reexamination Certificate
active
06466608
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to communication among plural nodes, and more particularly, to control of wireless communication among nodes using frequency hopping radio signals.
2. State of the Art
Communication systems, such as local area networks (LANs), have achieved widespread use for the exchange of information. These systems include a plurality of data processing nodes, or “agents”, which contend for access to a communication medium that interconnects the nodes.
Typical communication networks use hardwired interconnections, such as the local area network communication system described in U.S. Pat. No. 4,661,902 (Hochsprung et al). More recent efforts have been directed to developing wireless communication networks. For example, commonly assigned U.S. Pat. No. 5,231,634 (Giles et al) relates to a communication system for regulating communication among a plurality of nodes, each of which is equipped with a radio transceiver. The '634 patent describes medium access control of a wireless LAN to provide decentralized, peer-to-peer access for all of the agents. A peer-to-peer communication system is one in which all agents can freely communicate without any agent having an advantage over another.
Wireless communication systems require consideration of potential problems which do not exist in hardwired systems. For example, in a wireless communication system, the nodes can be mobile, moving in and out of range with other nodes in the system. The '634 patent is directed to continuously ensuring that all agents possess fair access to the communication system (i.e., to avoid, for example, agents which are physically closer to a given destination from having an unfair advantage due to their signal strength being greater than that of agents physically located further from the destination).
Due to their unique considerations, wireless communication systems have not been developed which can exploit communication techniques such as frequency hopping. Frequency hopping is a known spread-spectrum technique whereby a signal is transmitted using a plurality of frequencies. The exact frequency used at any given time is switched from one frequency to another either in a random or a predetermined sequence.
Frequency hopping techniques provide reliable and secure wireless communication. However, conventional frequency hopping techniques are not readily adaptable to a wireless LAN environment, such as the LAN described in the '634 patent. For example, in frequency hopping systems, synchronization among transmitting and receiving stations constitutes a significant problem. In a LAN environment, synchronization becomes a more significant problem since nodes can move into and out of any number of dynamically changing, reconfigurable communication systems, each of which can have an independently synchronized frequency hopping sequence. There is presently no mechanism for establishing and maintaining synchronization among the nodes present in a dynamically changing, reconftigurable communication system.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to providing wireless frequency hopping communication among a plurality of nodes. For example, the present invention is directed to features such as (1) synchronizing frequency hopping communication of a dynamically changing, wireless communication system having plural nodes; and (2) automatically resolving which of the plural nodes of the dynamically changing communication system is best suited to control synchronization (e.g., which node can establish synchronized communication among the greatest number of nodes at any given time). Exemplary embodiments provide decentralized control of synchronization whereby a master node used to control synchronization of the communication system can dynamically change as the communication system is dynamically reconfigured.
Generally speaking, exemplary embodiments of the present invention relate to an apparatus and method for controlling frequency hopping communication among plural nodes in a communication system by transmitting a synchronization signal from a first node during a predetermined contention-free synchronization period; and synchronizing frequency hopping of at least a second node to said first node via said synchronization signal.
Embodiments of the present invention also relate to an apparatus and method for controlling frequency hopping communication among plural nodes in a communication system by assigning each of the nodes a hierarchical designation representing a priority of the node to control synchronization of the communication system; initializing the communication system by synchronizing the nodes to a first node; searching the communication system to locate a second node to control synchronization of the communication system; and synchronizing the communication system to the second node if located.
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Harry Newton, Newton's Telecom Dictionary, p. 777, 1994.
Coleman Arthur
Giles Rick R.
Grau Juan
Hong Hilton
Burns Doane , Swecker, Mathis LLP
Luther William
Proxim Inc.
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