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United States Patent [w]
US005875179A [ii] Patent Number: 5,875,179  Date of Patent: Feb. 23, 1999
 METHOD AND APPARATUS FOR
SYNCHRONIZED COMMUNICATION OVER
WIRELESS BACKBONE ARCHITECTURE
 Inventor: Terry L. Tikalsky, Sunnyvale, Calif.
 Assignee: Proxim, Inc., Mountain View, Calif.
 Appl. No.: 739,224
 Filed: Oct. 29, 1996
 Int. CI.6 H04J 3/06; H04J 13/06;
 U.S. CI 370/315; 370/342; 370/350;
370/516; 375/202; 375/371
 Field of Search 370/254, 255,
370/256, 315, 320, 335, 342, 350, 441, 479, 503, 516; 375/202, 205, 354, 356, 371; 455/507, 509
 References Cited
U.S. PATENT DOCUMENTS
5,121,408 6/1992 Cai et al 375/202
5,231,634 7/1993 Giles et al 370/348
5,428,636 6/1995 Meier 370/256
5,442,659 8/1995 Bauchot et al 375/202
5,453,977 9/1995 Flammer, III et al 370/254
5,509,027 4/1996 Vook et al 375/202
5,696,903 12/1997 Mahany 395/200.58
Primary Examiner—Hassan Kizou
Attorney, Agent, or Firm—Burns, Doane, Swecker & Mathis LLP
The present invention is directed to providing wireless communication among a plurality of nodes and repeaters that are synchronized for communication with a central hub that constitutes a master repeater. For example, the present invention is directed to a wireless network having a wireless backbone of repeaters which can use frequency hopping to automatically establish synchronization despite dynamic changes in the wireless communication system. Exemplary embodiments provide for control of synchronization whereby a repeater, when introduced to the system, automatically scans for, and synchronizes to another repeater, while at the same time continuing to listen for other repeater signals which identify either the master repeater, or another repeater which is closer to the master repeater (i.e., communicates to the master repeater through a more direct communication link).
16 Claims, 2 Drawing Sheets
METHOD AND APPARATUS FOR
SYNCHRONIZED COMMUNICATION OVER
WIRELESS BACKBONE ARCHITECTURE
BACKGROUND OF THE INVENTION 5
1. Field of the Invention
The present invention relates generally to synchronizing communication among plural nodes in a communications system and more particularly, to synchronizing communi- 10 cation among plural nodes which communicate within a network having a wireless backbone of repeaters.
2. State of the Art
Communication systems, such as local area networks (LANs), have achieved widespread use for the exchange of :5 information. These systems include a plurality of data processing nodes or "agents", which access a transmission medium that interconnects the nodes. Many local area network schemes have been devised for providing the nodes with a shared access network, or backbone, through which 20 the nodes communicate with each other or with a central hub, or server. Where plural nodes of a network are synchronized to a central hub, local area network schemes have been devised with a central hub organization wherein a backbone of nodes which function as repeaters are intercon- 25 nected by a wired communication path. Non-repeater nodes are connected to repeater nodes which are directly, or via other repeater nodes, connected to the central hub. These network arrangements typically involve hardwire connections. 30
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 35 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 40 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 4J and repeaters can be mobile, moving in and out of range of other nodes and repeaters 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 5Q destination from having an unfair advantage due to their signal strength being greater than that of agents physically located further from the destination).
Wireless systems also require consideration of radio transmission limits imposed by a physical setting, or even by 55 FCC regulations regarding radio emissions. Due to these considerations, wireless networks, such as the one described in the '634 patent, may have restricted operating flexibility.
Due to their unique considerations, wireless communication systems have not been developed which can freely 60 exploit communication techniques such as central hub organization. Central hub organization is a network scheme involving use of a central, or master repeater, that controls the operation of the network. The master repeater may communicate directly with non-repeater nodes or, in widely 65 distributed networks, through the use of repeater nodes. For purposes of this discussion, both repeater and non-repeater
nodes are referred to as "nodes" while repeaters are also referred to as "repeaters". The repeaters in a master repeater network facilitate the propagation of data, control and synchronization information to the nodes, including other repeaters. The repeaters may be in direct contact with the master repeater or, may be in contact with another repeater that is directly or indirectly in contact with a master repeater.
Because of the constraints associated with wireless network schemes, such schemes have at most been used for communications between the nodes and the repeaters of a central hub architecture and not for communications between repeaters. By limiting wireless communications to communications between nodes and repeaters, interference of signals within the overall network can be controlled. For example, all nodes which communicate to the central hub via a first repeater can communicate with the first repeater on a first frequency channel, while all nodes which communicate with the central hub via a second repeater can communicate with the second repeater on a second frequency channel. The nodes connected to a given repeater thus constitute a sub-network, or domain. Each of the repeaters can then communicate with the central hub via a wired link through any number of repeaters to ensure reliable communications. Because repeaters typically handle increased communications (i.e., communications from nodes connected directly to the repeater as well as communication to and from linked repeaters) reliable communication between repeaters can thus be ensured with wired links.
Although techniques exist for enhancing the reliability of wireless communications, these techniques have not been considered practical for use in interconnecting a backbone of repeaters. For example, 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 is useful in preventing fading errors, and is generally more secure than single channel communication.
While frequency hopping techniques provide reliable and secure wireless communication, conventional frequency hopping techniques are not readily adaptable to a wireless LAN environment, and in particular, a wireless LAN environment which includes a backbone of repeaters which can move into and out of any number of dynamically changing, reconfigurable arrangements. Further, the need to maintain a high level of synchronization for wireless communication has been considered to render its use impractical for high traffic repeaters which are located in communication networks that operate with a number of different frequency channels (e.g., a different frequency channel for each repeater).
It would therefore be desirable to provide the advantages of a central hub organization which exploits the use of wireless links for communication between nodes and repeaters, and for communication between repeaters and a central hub. Further it would be desirable to provide some mechanism for establishing and maintaining synchronization among the repeaters in a dynamically changing, reconfigurable communication system.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to providing wireless communication among a plurality of nodes that are synchronized for communication with a central hub that constitutes a master repeater. For example, the present invention is directed to a wireless network having a wireless