Distributed control methods for management of migrating data stations in a wireless communications network

Claims

Having thus described my invention, what I claim as new, and desire to secure by Letters Patent is:

1. A method for managing ownership of one or more mobile communication units in a wireless communications network, the wireless communications network having a plurality of header stations in bidirectional wireless communication over the wireless communications network with one or more of the mobile communication units, the method comprising the steps of:

periodically transmitting a first message over the wireless communications network from each of the plurality of header stations, the transmitted first message including information for uniquely identifying the transmitting header station and also including information for specifying a number of mobile communication units for which the transmitting header station is presently managing wireless communications;

receiving, with a mobile communication unit located at a position that is served by two or more of the header stations, the transmitted first message from each of the header stations that serve the position occupied by the mobile communication unit, the transmitted first messages being received over the wireless communications network;

selecting, with the mobile communication unit in accordance with the received transmitted first messages from the two or more header station as, one of the header stations as a header station to manage future wireless communications for the mobile communication unit; and

if the selected header station is not a header station that is presently managing wireless communications for the mobile communication unit, transmitting a second message over the wireless communications network from the mobile communication unit to the selected header station, the transmitted second message requesting that wireless communications for the mobile communication unit be managed by the selected header station.

2. A method as set forth in claim 1 wherein the step of selecting includes the following steps:

determining if the received transmitted first message originated from a header station that is presently managing wireless communications for the mobile communication unit; and, if so

determining if a strength of the received transmitted first message is above a predetermined threshold; and, if so

retaining the header station that is presently managing wireless communications for the mobile communication unit.

3. A method as set forth in claim 2 wherein if the header station that is presently managing wireless communications for the mobile communication unit is not retained, the step of selecting further includes the steps of:

determining from the received transmitted first messages the number of other mobile communication units that are currently managed by each of the header stations that serve the position occupied by the mobile communication unit; and

selecting a header station that is managing wireless communications for the fewest number of other mobile units; or

if all of the header stations that serve the position occupied by the mobile communication unit are determined to be managing a same number of other mobile communication units,

selecting the header station having a received signal strength that exceeds the received signal strengths of the other header stations by a predetermined amount; or

if none of the header stations that serve the position occupied by the mobile communication unit are determined to have a received signal strength that exceeds that of the other header stations by the predetermined amount,

selecting one of the header stations at random.

4. A method as set forth in claim 1 and further comprising the steps of:

receiving at the selected header station the second message transmitted by the mobile communication unit; and

notifying the mobile communication unit that the selected header station has accepted the mobile communication unit for inclusion within a set of mobile communication units for which the selected header station is managing wireless communications.

5. A method as set forth in claim 1, wherein the second message includes information for identifying a header station, if any, that is currently managing wireless communications for the mobile communication unit, and further comprising the steps of:

receiving at the selected header station the second message transmitted by the mobile communication unit;

determining, with the selected header station, if wireless communications for the mobile communication unit was previously managed by another header station; and, if so,

informing the other header station, from the selected header station, that the mobile communication unit is now managed by the selected header station.

6. A method as set forth in claim 5 and further comprising a step of notifying, with the selected header station, all other header stations that maintain a communications routing table that includes the mobile communication unit, that the mobile communication unit is now managed by the selected header station.

7. A method as set forth in claim 1 wherein the step of receiving occurs for a period of time determined to be sufficiently long so as to receive at least one transmitted first message from each of the header stations that serve the position occupied by the mobile communication unit.

8. A method as set forth in claim 1 wherein the step of receiving occurs for a period of time at least equal to (.DELTA.+.epsilon.), where delta is a predetermined time interval and wherein epsilon is a variable time period, the period of time being sufficiently long so as to receive at least one transmitted first message from each of the header stations that serve the position occupied by the mobile communication unit.

9. A method as set forth in claim 1 wherein the step of transmitting the second message includes a step of transmitting a message including at least an identification of the mobile communication unit, an identification of a header station, if any, having a domain of which the mobile communication unit is currently a member, and an identification of the selected header station.

10. A method as set forth in claim 6 wherein the steps of informing and notifying each include a step of transmitting a message over a wired network that is coupled between the header station and others of the header stations.

11. A method as set forth in claim 1 wherein each of the header stations is bidirectionally coupled to a wired network, and wherein the selected header station records an identification of the second header station in response to a receipt of a message from the wired network that is directed to the mobile communication unit from a second header station.

12. A method as set forth in claim 11 wherein the selected header station, in response to a receipt of a message from the wired network from a third header station, the received message from the third header station indicating that the mobile communication unit has selected the third header station to manage wireless communications for the mobile communication unit, transmits a message over the wired network to the third header station, the message that is transmitted to the third header station including the identification of the second header station.

13. A method as set forth in claim 12 wherein the third header station, upon receipt of the message from the previously selected header station, transmits a message over the wired network to the second header station to inform the second header station that the third header station is managing wireless communications for the mobile communication unit.

14. A method as set forth in claim 13 wherein the second header station updates an internally maintained routing table in response to a receipt of the message from the third header station such that a subsequent message that is directed to the mobile communication unit is transmitted over the wired network from the second header station to the third header station.

15. A method as set forth in claim 12 wherein the third header station updates an internally maintained status table in response to a receipt of the message from the previously selected header station such that the third header station is enabled to determine what other header stations, if any, have previously directed a message to the mobile communication unit.

16. A wireless communications system having a plurality of header stations each serving a communication coverage area, the system further including at least one mobile communication unit, the mobile communication unit comprising:

means for receiving, when located at a position that is served by two or more of the header stations, a transmission from each of the header stations that serve the position occupied by the mobile communication unit, the received transmissions being received over the wireless communications network and each transmission including information for uniquely identifying the transmitting header station, each transmission further including other information for indicating a number of mobile communication units for which the transmitting header station is currently managing wireless communications;

means for selecting, in accordance with the received transmissions from the two or more header stations, one of the header stations as a header station to manage future wireless communications for the mobile communication unit; and

means for transmitting a message over the wireless communications network from the mobile communication unit to the selected header station, the transmitted message requesting that the mobile communication unit be assigned to the selected header station, said transmitting means operating in response to a determination by the mobile communication unit that the selected header station is not a header station that is presently managing wireless communications for the mobile communication unit, the transmitted message including information for identifying a header station, if any, that is currently managing wireless communications for the mobile communication unit.

17. A wireless communications system as set froth in claim 16 and further including a wired network for coupling together the plurality of header stations such that the header stations are enabled to communicate messages one to another, one type of message being transmitted over the wired network from the selected header station to a previously selected header station to inform the previously selected header station that the selected header station is now managing wireless communications for the mobile communication unit.

18. A wireless communications system as set forth in claim 16 wherein each of the header stations and the mobile communication unit include means for transmitting an infrared radiation signal to the wireless communications network and means for receiving an infrared radiation signal from the wireless communications network.

19. A wireless communications system as set forth in claim 16 wherein the mobile communication unit further includes:

means for storing a list of header stations that are determined by the mobile communication unit to be potential owners of the mobile communication unit; and

means for updating the list in response to the received transmissions;

and wherein each of the header stations includes means for storing a communications routing table associated with one or more mobile communication units that are owned by the header station.

20. A method for managing ownership of one or more mobile communication units in a wireless communications network, the wireless communications network having a plurality of header stations in bidirectional wireless communication with one or more of the mobile communication units, the method comprising the steps of:

receiving, with a mobile communication unit located at a position that is served by two or more of the header stations, a transmission from each of the header stations that serve the position occupied by the mobile communication unit, the received transmissions being received over the wireless communications network, each transmission uniquely identifying the transmitting header station;

selecting, with the mobile communication unit and in accordance with the received transmissions from the two or more header stations, one of the header stations as a header station to manage future wireless communications for the mobile communication unit; and

if the selected header station is not a header station that is presently managing wireless communications for the mobile communication unit, transmitting a message over the wireless communications network from the mobile communication unit to the selected header station requesting that the selected header station manage future wireless communications for the mobile communication unit;

wherein the selected header station, in response to a message directed to the mobile communication unit from a second header station, records an identification of the second header station; and wherein

the selected header station, in response to a message from a third header station that indicates that the mobile communication unit has selected the third header station to manage wireless communications for the mobile communication unit, transmits a message to a a third header station, the message including the identification of the second header station.

21. A wireless data communications system, comprising:

a plurality of header stations, each of said header stations including means for transmitting information to a wireless network and means for receiving information for the wireless network, each of said header stations having a wireless communication cell associated therewith, each of said header stations further including means for bidirectionally coupling the header station to a wired network for transmitting information to the wired network and for receiving information from the wired network, wherein at least some of the information that is transmitted to the wired network is information that is first received from the wireless network, and wherein at least some of the information that is transmitted to the wireless network is information that is first received from the wired network; and

at least one mobile data station, said mobile data station including,

means for receiving, when located at a position where two or more wireless communications cells overlap, a transmission from each of the header stations associated with the overlapping wireless communications cells, each of the transmissions including information for uniquely identifying the transmitting header station, each transmission further including other information for indicating a number of mobile data stations for which the transmitting header station is currently managing wireless data communications;

means for selecting, in accordance with the received transmissions from the two or more header stations, one of the header stations as a header station to manage future wireless communications for the mobile data station; and

means for transmitting a message over the wireless communications network from the mobile data station, the transmitted message including information for uniquely identifying the mobile data station, information for specifying an identification of a header station, if any, that is currently managing wireless communications for the mobile data station, and information for specifying the identification of the selected header station, said transmitting means operating in response to a determination by the mobile communication unit that the selected header station is not a header station that is presently managing wireless communications for the mobile communication unit.

22. A wireless data communications system as set forth in claim 21 wherein each of the header stations and the mobile data station include means for transmitting an infrared radiation signal to the wireless communications network and means for receiving an infrared radiation signal for the wireless communications network.

23. A wireless data communications system as set forth in claim 21 wherein the mobile data station includes means for storing a list of header stations that are determined by the mobile data station to be potential owners of the mobile data station, and wherein each of the header stations includes means for storing a communications routing table having entries for at least each of the mobile data stations for which the header station is currently managing wireless data communications.

FIELD OF THE INVENTION

This invention relates generally to communication methods and, in particular, to a method of managing domain and ownership relationships of mobile communication units in a wireless network having fixed header stations with overlapping communication cells.

BACKGROUND OF THE INVENTION

In a local area network (LAN) environment a user, such as a portable computer equipped with communication capability, gains access to the LAN via a physical connection in order to communicate with remote facilities or use shared resources, such as file servers, print servers, etc. In a stationary mode of operation, all users are static and each user gains access to the network via a fixed homing point. However, in a mobile environment users are free to change their physical location and cannot be restricted to gain access to the network only through one of several homing points attached to the LAN. In a mobile environment the homing points are fixed header stations that communicate with the mobile units through a wireless link. Examples of wireless links include radio frequency (RF) links, microwave links and infrared (IR) links.

For example, a wireless network may include two Header Stations (HS.sub.1 and HS.sub.2) attached to a wired network. Each header station has an associated wireless communication coverage area, or cell. All communication traffic originating from or destined for a first mobile data processing unit is managed by HS.sub.1, also considered to be the "owner" of the first mobile data processing unit. Similarly, all communication traffic originating from or destined for a second mobile data processing unit is managed by HS.sub.2, the owner of the second mobile data processing unit. As a user moves from one physical location to another, the header station responsible for managing the communication needs of the user must also change. Management of the communications needs of a mobile unit includes routing messages from the mobile unit to the LAN and broadcasting messages from the LAN to the mobile unit.

As a mobile unit moves from cell to cell, the mobile unit's owner is required to change. The type of mobile communication of interest herein implies that mobile units communicate with one another, via a header station or stations, using symbolic names and without any specific reference to a physical location at which the mobile unit may presently be positioned. As such, a number of suitable communication protocols are required to manage the change in ownership of a given mobile unit as it changes position relative to the fixed header stations. These protocols include the following.

(a) Establishment of unique ownership for each mobile unit that become active, or turned on, for the first time in the system.

(b) Detection of movement of mobile units as they cross from one communication cell to another.

(c) Accomplishing the change of ownership of mobile units as movement from one cell to another occurs.

(d) The assignment of a unique owner to a mobile unit positioned in an area of overlap between two header stations and wherein the mobile unit could potentially be serviced by either of the header stations.

(e) Readjustment of routing related information at header stations that are affected by the movement of a mobile unit.

An underlying concern in implementing these protocols is a consideration that mobile units are battery powered and that any implementation of the protocols must seek to conserve battery power. In this regard it is typically the case that an uplink transmission, from the mobile unit to the header station, places significantly more demand on battery power than the reception of a downlink transmission from the header station to the mobile unit. Thus, a protocol that minimizes the number of uplink transmissions is preferable to one that may require many uplink transmissions for accomplishing the same function.

The following U.S. Patents and articles are made of record for teaching various aspects of mobile communication.

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. Yamauchi et al. provide for a hand-off of a subscriber station from one header station to another by the header 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. 4,792,946, 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 together in a loop.

In U.S. Pat. No. 4,777,633, issued Oct. 11, 1988, entitled "Base Station for Wireless Digital Telephone System" Fletcher et al. describe a base station that communicates with subscriber stations by employing a slotted communications protocol.

In U.S. Pat. No. 4,730,310, issued Mar. 8, 1988, entitled "Terrestrial Communications System" Acampora et al. describe a communications system that employs spot beams, TDMA and frequency reuse to provide communication between a header station and remote stations.

In U.S. Pat. No. 4,655,519, issued May 12, 1987, entitled "Wireless Computer Modem" Kirchner et al. disclose a wireless modem for transferring data in a computer local area network.

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. 4,837,858, issued Jun. 6, 1989, entitled "Subscriber Unit for a Trunked Voice/Data Communication System" Ablay et al. disclose a trunked voice/data subscriber that operates in either a voice mode or one of three data modes.

In U.S. Pat. No. 4,852,122, issued Jul. 25, 1989, entitled "Modem Suited for Wireless Communication Channel Use" Nelson et al. disclose a wireless communication system and, specifically, a modem that communicates digital data with data terminal equipment.

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 which 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 describes a LAN wherein 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 commonly assigned 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. 20, No. 7, December 1977 F. Closs et al. describe the use of both line-of-sight and diffuse transmission of infrared signals for wireless communications between a ceiling-based controller and a plurality of terminals.

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 by this prior art, and what is thus an object of the invention to provide, are communication methodologies that realize, in a wireless communications network, the protocols (a)-(e) described above.

A further object of the invention is to accomplish the above referenced protocols (a)-(e) in a manner that makes efficient use of battery power of mobile units in a wireless communications network.

SUMMARY OF THE INVENTION

The foregoing and other problems are overcome and the objects of the invention are realized by a method for managing ownership of one or more mobile communication units within a wireless communications network. The wireless communications network has a plurality of header stations in bidirectional wireless communication with one or more mobile communication units. In accordance with the method the following steps are executed. A first step receives, with a mobile communication unit located at a position that is served by two or more of the header stations, a transmission from each of the header stations. The received transmissions are received over the wireless communications network and each uniquely identify the transmitting header station. The method further includes a step of selecting, with the mobile communication unit, one of the header stations as a header station to manage future wireless communications for the mobile unit. A further step is performed if the selected header station is not a header station that is presently managing wireless communications for the mobile unit This further step transmits a message over the wireless network from the mobile unit to the selected header station requesting that the mobile unit be assigned to the selected header station.

The step of selecting includes the steps of (a) determining if a received transmission originated from a header station that is presently managing wireless communications for the mobile unit; and, if so (b) determining if a strength of the received transmission is above a predetermined threshold; and if so (c) retaining the header station that is presently managing wireless communications for the mobile unit.

If the header station that is presently managing communications for the mobile unit is not retained the step of selecting further includes the steps of (d) determining a number of other mobile units that are currently managed by the header stations that serve the position occupied by the mobile unit; and (e) selecting the header station that is managing the fewest number of other mobile units. If all of the header stations that serve the position occupied by the mobile unit are determined to be managing a same number of other mobile units the method includes a further step of (f) selecting the header station having a signal strength that exceeds the signal strengths of the other header stations by a predetermined amount. If none of the header stations that serve the position occupied by the mobile unit are determined to have a signal strength that exceeds that of the other header stations by the predetermined amount, the method includes a further step of (g) selecting one of the header stations at random.

BRIEF DESCRIPTION OF THE DRAWING

The above set forth and other features of the invention are made more apparent in the ensuing Detailed Description of the Invention when read in conjunction with the attached Drawing, wherein:

FIG. 1a is a block diagram showing a plurality of mobile units communicating with a header station;

FIG. 1b is a block diagram of the header station of FIG. 1a;

FIG. 1c is a block diagram of the mobile unit of FIG. 1a;

FIG. 2 shows a plurality of overlapping header station communication cells;

FIG. 3 is a flow chart illustrating a method performed by a mobile unit in selecting a new header station having a domain to which the mobile unit is to become associated;

FIG. 4a shows the format of an inquiry message that is periodically transmitted from a header station to all mobile units within the communication cell of the header station;

FIG. 4b shows the format of a message transmitted from a mobile unit to specific header station having a domain that the mobile unit has determined that it will become a member of;

FIG. 5 is a flow chart illustrating a method performed by the mobile unit in determining a new header station having a domain to which the mobile unit is to become associated;

FIG. 6 is a flow chart illustrating a method performed by the header station in adding a mobile unit to its associated domain; and

FIG. 7 diagrammatically shows an interaction between three header stations caused by the migration of a mobile unit from the domain of one of the header stations to the domain of another of the header stations.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1a depicts an embodiment of the invention wherein a mobile data station 10 is in bidirectional communication over an optical radiation communications channel with a network adapter, also referred to herein as a header station 12. The header station 12 is coupled via a connector 14 to a wired local area network (LAN) 16. As shown the header station 12 is disposed within or adjacent to a ceiling 18 and the mobile unit 10 is carried or is otherwise transported over a floor 20. Of course, the mobile unit 10 may be used in a stationary manner if desired.

The communications channel is carried via an infrared (IR) data link. Presently available optical devices readily provide for operation within the range of approximately 750 nanometers to approximately 1000 nanometers.

Referring to FIG. 1b there is shown a simplified block diagram of the header station 12. The header station 12 is coupled to the LAN 16 via the connector 14. Connector 14 is coupled to a network adapter transceiver 22 which in turn is coupled to an internal bus 24. The header station 12 includes a processor 26 that is bidirectionally coupled to a memory 28 that stores program-related and other data, including packets of data transmitted to or received from the mobile units 10. Also bidirectionally coupled to the processor 26 is a time keeping unit, or clock 27, the use of which is described below. Processor 26 also communicates with IR modulators and receivers; specifically a modulator 30a and a receiver 30b. The IR modulator and receiver have inputs coupled to suitable infrared emitting or receiving devices such as laser diodes