Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-08-26
2003-07-22
Marcelo, Melvin (Department: 2663)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S338000, C375S132000
Reexamination Certificate
active
06597671
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to communications systems and, in particular such communications in a wireless local area network (LAN). Specifically, the invention is directed to assignment of network resources in communication systems using shared multiple access communication media, such as, for instance, frequency hopping patterns, in a multicell radio LAN based on slow frequency hopping spread spectrum signaling.
BACKGROUND OF THE INVENTION
In a wireless LAN network various configuration parameters or network resources have to be maintained and distributed as base stations and remote stations enter or leave the network. A typical wireless LAN topology is divided into cells. Associated with each cell is a base station connected to a backbone network which acts as an access point and relay for remote stations. To become part of the network, remote stations have to register with one of the base stations. All communications between the remote station and other entities are subsequently handled by the base station with which the remote station has registered. For instance a multicell radio LAN installation based on slow frequency hopping spread spectrum signaling may consist of a set of base stations with overlapping coverage areas. In a frequency hopping (FH) system, the carrier frequency of the transmitter changes at intervals of time, remaining constant between those instants. The period of constant frequency is called a hop and messages may be exchanged during these hops. Efficient methods for controlling and minimizing radio interference between overlapping cells are essential to the reliability and performance of such radio LAN installations. The transmission and reception of messages in a cell of a multicell network of the type that employs identical communication frequencies in different cells, requires control of interference between users. This interference may occur from several sources including transmission from remote stations that lie in overlapping areas between adjacent cells and transmissions from base stations if these overlapping cell areas contain one or more remote users. Assigning different frequency hopping sequences or patterns to base stations with overlapping coverage areas allows to control and limit interferences.
The following U.S. Patents and European Patent applications teach various aspects of mobile communications using wireless transmission media.
U.S. Pat. No. 5,239,673 teaches a scheduling method for efficient frequency reuse in a multi-cell wireless network served by a wired local area network. One method of the invention circulates a high priority token among a plurality of header stations connected to the wired network. Reception of the token causes the receiving header station to perform wireless communications. When finished, the header station forwards the token to another header station.
The following two U.S. Patents show communication systems having overlapping coverage areas: U.S. Pat. No. 4,597,105, Jun. 24, 1986, entitled “Data Communications System having Overlapping Receiver coverage Zones” to Freeburg and U.S. Pat. No. 4,881,271 issued Nov. 14, 1989, entitled “Portable Wireless Communication Systems” to Yamauchi et al. provide for a hand-off of a subscriber station from one base station to another by the base station continually monitoring the signal strength of the subscriber station.
The following U.S. Patents teach various aspects of wireless communication networks.
In U.S. Pat. No. 4,792,942, issued Dec. 20, 1988 entitled “Wireless Local Area Network for Use in Neighborhoods” S. Mayo describes a local area network that includes transceiver stations serially coupled in a loop.
In U.S. Pat. No. 4,730,310 issued Mar. 8, 1988 entitled “Terrestrial Communications Systems” Acampora et al. describe a communications system that employs spot beams, TDMA and frequency reuse to provide communication between a base station and remote stations.
In U.S. Pat. No. 4,639,914, issued Jan. 27, 1987 entitled “Wireless PBX/LAN System with Optimum Combining” Winters discloses a wireless LAN system that employs adaptive signal processing to dynamically reassign a user from one channel to another.
In U.S. Pat. No. 4,926,495, issued May 15, 1990 entitled “Computer Aided Dispatch System” Comroe et al. disclose a computer aided dispatch system that includes a master file node and a plurality of user nodes. The master file node maintains a record for each subscriber and automatically transmits an updated record to each dispatcher attached to a subgroup in which the subscriber operates.
In U.S. Pat. No. 4,456,793, issued Jun. 26, 1984 W. E. Baker et al. describe a cordless telephone system having infrared wireless links between handsets and transponders. The transponders are wired to subsystem controllers that are in turn wired to a system controller. The central controller polls the cordless stations every 100 milliseconds to detect cordless station locations and to identify “missing” cordless stations.
In U.S. Pat. No. 4,807,222, issued Feb. 21, 1989 N. Amitay described a LAN in which users communicate with RF or IR signals with an assigned Regional Bus Interface Unit (RBIU). Protocols such as CSMA/CD and slotted ALOHA are employed in communicating with the RBIUs.
In U.S. Pat. No. 4,402,090 issued Aug. 30, 1983, F. Gfeller et al. describe an infrared communication system that operates between a plurality of satellite stations and a plurality of terminal stations. A host computer communicates with the terminal stations via a cluster controller and the satellite stations, which may be ceiling mounted. Communication with the terminal stations is not interrupted even during movement of the terminal stations.
In IBM Technical Disclosure Bulletin, vol. 24, No 8, page 4043, January 1982 F. Gfeller describes general control principles of an infrared wireless network incorporating multiple ceiling mounted transponders that couple a host/controller to multiple terminal stations. Access to the uplink channel is controlled by a Carrier Sense Multiple Access/Collision Detection (CSMA/CD) method.
What is not taught in the prior art is a method for reusing frequency hopping patterns thus allowing to operate such frequency hopping wireless LAN's with a number of base stations greater than the number of existing frequency hopping patterns. More generally such method applies to the allocation of other kinds of network resources, such as a limited pool of remote stations addresses. In addition the method of the invention applies as well to wireless systems using different signalling techniques such as for instance direct sequence spread system radio frequency signalling or infrared and more generally to any communication system using a multiple access shared communication medium.
SUMMARY OF THE INVENTION
The invention as defined is to provide a method for reusing a limited number of network resources in a communication system using a multiple access shared communication medium such as a wireless radio frequency (RF) or infrared (IR) communication network comprised of a local area network connected to a plurality of base stations. Each base station has a geographic area, defined as a cell, within which remote stations are within reception range. Remote stations select one base station as home base station. Home base stations are capable of performing bidirectional communication with one or more remote stations under control of a controller connected to said local area network, the method of the invention comprises the steps of:
(a) requesting by a given base station assignment by said controller of one of said network resources; and
(b) selecting and assigning by said controller one of said network resources;
This method allows to select and assign one of the network resources already assigned to one or more other base stations. Selection is based on the computation by the controller of a distance index between the given base station and the other base stations. The resource assigned to the given base station is the one already assigned t
Ahmadi Hamid
Bantz David
Bauchot Frederic
Harrison Colin
Krishna Arvind
Cockburn Joscelyn G.
Marcelo Melvin
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