US005960344A
`5,960,344
`(114) Patent Number:
`United States Patent 55
`Mahany
`[45] Date of Patent:
`Sep. 28, 1999
`
`
`[54] LOCAL AREA NETWORK HAVING
`MULTIPLE CHANNEL WIRELESS ACCESS
`
`[75]
`
`Inventor: Ronald L. Mahany, Cedar Rapids,
`Towa
`[73] Assignee: Norand Corporation, Cedar Rapids,
`Iowa
`
`[21] Appl. No.: 08/878,357
`[22]
`Filed:
`Jun.27, 1997
`
`Related U.S. Application Data
`
`[63] Continuation-in-part of application No. 08/772,895,filed as
`application No. PCT/US96/09474, Jun. 3, 1996, abandoned,
`which is a continuation-in-part of application No. 08/696,
`086, Aug, 13, 1996, abandoned, which is a continuation of
`application No. 08/238,180, May 4, 1994, Pat. No. 5,546,
`397, which is a continuation-in-part of application No.
`08/197,392, Feb. 16, 1994, abandoned, which is a continu-
`ation-in-part of application No. 08/170,121, Dec. 20,1993,
`abandoned.
`Tint, Cdeee ccccsssecceessseessssseseessnees H04Q 7/00
`[51]
`[52] U.S. Ch. eee 455/432; 455/434; 455/435
`[58] Field of Search oo... 455/432, 435,
`455/455, 450, 517, 582, 515, 553, 78, 434;
`370/310, 311, 328, 329, 330, 335
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`9/1991 Halll et ale uccccccsseeccssssseeeeeen 455/78
`wee 455/422
`4/1996 Vannucci...
`
`........
`w 455/562
`8/1996 Fujii et al.
`10/1996 Bendixen etal. occ 455/434
`
`5,046,130
`5,513,184
`5,551,060
`5,561,845
`
`8/1997 Tusa et al. seessssssssssssestensen 455/435
`5,655,219
`
`3/1998 Raith et al. oes 370/329
`5,734,645
`6/1998 Raith et al. o.eecceeeeee 455/434
`5,768,267
`Primary Examiner—Salvatore Cangialosi
`Attorney, Agent, or Firm—Akin, Gump, Strauss, Hauer &
`Feld, L.L.P.
`“
`[57]
`
`ABSTRACT
`
`A communication network having at least one access point
`supports wireless communication amonga plurality of wire-
`less roaming devices via a first and a second wireless
`channel. The access point comprises a first and a second
`transceiver. The first and second transceivers operate on the
`first and second wireless channels, respectively. Each of the
`plurality of wireless roaming devices are capable of com-
`municating on the first and second wireless channel. In one
`:
`:
`:
`embodiment, the first wireless channel is used to exchange
`data, while the second channel is used to manage such
`exchanges as well as access to the first channel. In an
`alternate embodiment, both channels are used to support
`communication flow, however the first channel supports a
`protocol that is more deterministic than that of the second
`channel. Allocation of ones of the plurality of wireless
`roaming devices from one channel to the next may occur per
`direction from the access point. It may also result from
`decisions made by each of the wireless roaming devices
`made independent of the access point. For example, a
`decision may be made based on the data type being trans-
`ferred or based on the current channel load. Such factors
`may also be used by the access point for allocation deter-
`minations. In addition, allocation may be based on the type
`of roaming deviceinvolved, suchasallocating peripherals to
`a slower channel.
`
`28 Claims, 17 Drawing Sheets
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`U.S. Patent
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`Sep. 28, 1999
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`U.S. Patent
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`Sep. 28, 1999
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`Sep. 28, 1999
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`U.S. Patent
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`Sep. 28, 1999
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`Sep. 28, 1999
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`5,960,344
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`Sep. 28, 1999
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`5,960,344
`
`1
`LOCAL AREA NETWORK HAVING
`MULTIPLE CHANNEL WIRELESS ACCESS
`
`CROSS-REFERENCE To RELATED APPLICATIONS
`The present application is a continuation-in-part of US.
`application Ser. No. 08/772,895 filed Dec. 24, 1996, now
`abandoned, which is a continuation-in-part of U.S. applica-
`tion Ser. No. 08/696,086 filed Aug. 13, 1996, abandoned,
`whichis a continuation of U.S. application Ser. No. 08/238,
`180 filed May 4, 1994, now issued as U.S. Pat. No. 5,546,
`397, which is a continuation-in-part of U.S. application Ser.
`No. 08/197,392 filed Feb. 16, 1994, now abandoned which
`is a continuation-in-part of U.S. application Ser. No. 08/170,
`121 filed Dec. 20, 1993 now abandoned.
`The U.S. application Ser. No. 08/772,895 filed Dec. 24,
`1996, now abandonedalso claims priority to PCT Applica-
`tion Ser. No. PCT/US96/09474, filed on Jun. 3, 1996.
`All of the aforementioned applications are hereby incor-
`porated herein by referencein their entirety. In addition, U.S.
`Pat. No. 5,425,051 issued Jun. 13, 1995 to Ronald L.
`Mahanyis also hereby incorporated herein by reference in
`its entirety.
`
`BACKGROUND
`
`1. Technical Field
`
`The present invention relates generally to access points
`used in wireless local area networks, and more specifically
`to an access point which includes multiple wireless adapters.
`2. Related Art
`
`Wireless local area networks (WLAN’s) use radio fre-
`quency transmissions to communicate between roaming
`computer devices and access points (or base stations). The
`access points are connected to an infrastructure that elec-
`tronically connects all of the access points to a host system.
`The wired infrastructure and the access points make up an
`information distribution network used for the transfer of
`information and for communications.
`
`In a wireless networking environment, various types of
`devices may need to communicate within a given area.
`When incompatibilities between device types arise,
`the
`wireless infrastructure must accommodate the various
`device types. Accommodating the different device types in
`a single infrastructure is generally difficult to accomplish.
`Further, devices within the wireless networking environ-
`ment typically communicate differing types of data, each
`with its own priority and bandwidth requirements. Accom-
`modating the various types of data with their related priori-
`ties often could not be accomplished by prior devices due to
`bandwidth limitations, conflicting priorities and incompat-
`ible standards within the wireless network.
`
`In prior WLANs,a first wireless terminal that desired to
`communicate with a base station often could not detect
`
`transmissions from a second wireless terminal currently
`engaged in ongoing communication with the access point.
`As a result, the wireless terminal often initiated transmis-
`sions that collided with the ongoing communications.
`Operation of this type is referred to as a “hidden terminal”
`situation. To solve the hidden terminal situation, some prior
`base stations were configured with a second transmitter for
`delivering a carrier signal on a “busy channel” wheneverthe
`base station was engaged in communication on the “data
`channel.” All
`terminals were also fitted with a second
`receiver, tuned to the busy channel, and required to check the
`busy channel before initiating communication on the data
`channel. However, the additional power required, bandwidth
`used, hardware needed and associated cost made the busy
`channel solution undesirable for most applications.
`
`10
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`2
`Some prior WLANsattempted to solve operational dif-
`ficulties by simply increasing the transmission capacity
`available on the infrastructure. Such expansion temporarily
`decreased conflicts in operation of the WLANs. However,
`the infrastructure, which is expensive to install, typically
`became overloaded quickly resulting in the same or similar
`problems.
`
`SUMMARYOF THE INVENTION
`
`The present invention is directed to communication net-
`work that supports communication within a premises. The
`communication network comprises an access point, a plu-
`rality of wireless roaming devices, a first wireless commu-
`nication channel, and a second wireless communication
`channel. The access point itself comprises a first processing
`circuit, a first radio transceiver coupledto the first process-
`ing circuit, and a second radio transceiver coupled to the first
`processing circuit. Each of the plurality of wireless roaming
`devices comprising a second processing circuit, a third radio
`transceiver and a radio receiver. Therein, the first wireless
`communication channel that supports communication flow
`via the communication network, while the second wireless
`communication channel
`is used to manage the flow of
`communication through the first wireless communication
`channel. In addition, the first and third radio transceivers are
`operable on the first wireless communication channel, while
`the second radio transceiver and the radio receiver are
`
`operable on the second wireless communication channel.
`The communication network also supports various other
`aspects of the present invention. For example, the access
`point may further comprises a wired communication inter-
`face circuit coupled to the first processing circuit. Selective
`participation on the first and second communication chan-
`nels may also provide further benefits. In one embodiment,
`each of the plurality of wireless roaming devicesutilizes the
`radio receiver on the second wireless communication chan-
`
`nel before participating with the third radio transceiver on
`the first wireless communication channel. In another, each
`utilizes the radio receiver on the second wireless commu-
`nication channel to gain access with the third radio trans-
`ceiver on the first wireless communication channel. Each
`may also or alternatively utilize the second wireless com-
`munication channel to identify ongoing communication on
`the first wireless communication channel to, perhaps, pro-
`vide an indication as to when channel capacity may become
`available.
`
`Other aspects may be found in an alternate communica-
`tion network which also supports communication within a
`premises. This communication network comprises an access
`point, first and second wireless communication channels and
`plurality of wireless roaming devices. The first wireless
`communication channel has first communication flow
`characteristics, while the second wireless communication
`channel has second communication flow characteristics. The
`first and second radio transceiversparticipate on the first and
`second wireless communication channels,
`respectively.
`Therein, each of the plurality of wireless roaming devices
`comprises a second processing circuit and meansfor selec-
`tively participating on the first and second wireless commu-
`nication channels.
`
`The access point may also comprise a wired communi-
`cation interface circuit coupled to thefirst processing circuit
`that may itself comprisea first and a second microprocessor.
`Additionally, at least one of the plurality of wireless roaming
`devices may participate on the first wireless communication
`channel while the other of the plurality of wireless roaming
`19
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`19
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`

`

`5,960,344
`
`3
`devices participates on the second wireless communication
`channel. Althoughthe at least one of the plurality of wireless
`roaming devices may participate on the first wireless com-
`munication channel as directed by the access device, other
`variations and combinations are also possible. For example,
`the at least one of the plurality of wireless roaming devices
`may participate on the first wireless communication channel
`to exchange a specific type of data, and/or may participate
`based on current channel conditions. Such participation may
`be based the fact that, in some embodiments, the second
`wireless communication channel is more deterministic than
`the first wireless communication channel.
`
`In any of the aforementioned embodiment, the commu-
`nication network may comprise at least a second access
`point. Other variations and aspects of the present invention
`will become apparentto ones of ordinary skill in the art after
`reviewing the entire specification and drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic representation of a high reliability
`access point in accordance with the present invention.
`FIG. 2 is a schematic representation of another high
`reliability access point of the present invention utilizing an
`antenna diversity scheme at each wireless adapter.
`FIG. 3 is a representation of a distribution network for a
`wireless LAN system utilizing high reliability access points.
`FIG. 4 is a schematic representation of a high reliability
`access point with a backup powersupply.
`FIG. 5 is a schematic representation of a remote high
`reliability access point connecting to the distribution net-
`work.
`
`10
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`20
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`25
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`30
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`4
`wherein an access point uses a dedicated control/obusy chan-
`nel transmitter to manage transmissions between the access
`point and a plurality of roaming portable data terminals
`within its cell.
`
`FIG. 12 is a drawing illustrating advantageous operation
`of the access device and portable data terminals of FIG. 11
`when two roaming terminals encounter hidden terminal
`conditions.
`
`FIG. 13 is a block diagram illustrating an alternate
`embodiment of the communication system of the present
`invention wherein an access point
`includes a dedicated
`control/busy channel transceiver and roaming data terminals
`communicate with the access point using either frequency
`nimble multi-channel transceivers or dedicated control/busy
`channeltransceivers.
`
`FIG. 14ais a block diagram illustrating a communication
`system of the present invention wherein access points and
`portable data terminals operate on a deterministic first
`channel and a non-deterministic second channel and the
`system routes communications on the channels based upon
`system conditions.
`FIG. 14d is a diagram illustrating operation of a commu-
`nication system of the present invention having both wired
`and wireless communication capability that includesat least
`one access point providing communication over
`a
`deterministic,
`time bounded first channel and a non-
`deterministic, contention access second channel.
`FIG. 15 is a diagram illustrating the use of the access
`points and portable data terminals of FIG. 14a wherein the
`system routes various transmissions within the network
`system according to system conditions such as channel
`activity, data type and data priority.
`DETAILED DESCRIPTION
`
`FIG. 6 is block diagram illustrating an embodimentof an
`access point built in accordance with the present invention
`which includes two radios and a wired network interface, a
`Referring now to the drawings wherein like reference
`first one of the radios operable on a first channel and a
`numerals designate identical or corresponding parts
`second one of the radios is operable on a second channel.
`throughoutthe several views, FIG. 1 showsa highreliability
`FIG. 7a is a block diagram illustrating an embodimentof
`access point 10 built in accordance with the present inven-
`a portable data terminal according to the present invention,
`tion. An access pointis a base station on a wireless local area
`the portable data terminal having a single PCMCIAcardthat
`network with which roaming portable or mobile computer
`contains two radios,afirst one of the radios operable on the
`devices can connect and communicate. The access point is
`first channel and a second oneofthe radios operable on the
`typically part of an overall distribution network which is
`second channel.
`connected to a host computer or entire computer local area
`network (LAN). The access points and the infrastructure
`make up the distribution network and allow for communi-
`cations between the roaming computer devices and the host
`computer or entire computer local area network (LAN).
`A highreliability access point 10 of the present invention
`includes a central processing unit CPU processor 13 and at
`least two wireless adapters 15 and 16. Each of the wireless
`adapters 15 and 16 include a radio 17 and 18, a media access
`control (MAC)processor 19 and 20 and an antenna 21 and
`22, respectively. The radios and antennas are used for RF
`transmission and reception. The MAC processor controls
`low level protocol functions including controlling the opera-
`tion of the radio, radio channel, error control, e.g., ARQ or
`Selective Response, and communication with the CPU pro-
`cessor 13. The CPU processor 13 controls the high level
`communications protocol functions and controls the inter-
`face 25 between the high reliability access point 10 and the
`infrastructure 26.
`In a preferred embodiment
`there is a
`PCMCIAstandard interface between the wireless adapters
`and the access point.
`The distribution network is comprised of all of the access
`points and the infrastructure which connectsall of the access
`points. A host computer or an entire host network is con-
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`FIG. 7b is a block diagram illustrating an alternative
`embodiment of the portable data terminal of FIG. 7a,
`wherein the single PCMCIAcard includes a single radio
`operable on the first channel and the second channel and
`controlled by the processing circuitry.
`FIG. 8 is a block diagram illustrating an alternative
`embodiment of a portable data terminal according to the
`present invention, the portable data terminal having a single
`PCMCIAcard that contains a multi-channel wireless trans-
`ceiver and a wired network interface.
`
`FIG. 9 is a diagram illustrating a communication system
`built and operating according to the present invention, the
`communication system including at least one access point
`having multiple radios, portable terminals having multiple
`radios and portable terminals having multi-channel radios.
`FIG. 10 is a diagram illustrating a communication system
`built and operating according to the present
`invention
`wherein one of the access points facilitates communication
`between portable terminal units operating on different chan-
`nels within its cell by routing communication between two
`of its radios.
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`a communication system according to the present invention
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`nected to the distribution network. The distribution network
`allows computer devices to communicate with the host
`computer or host network.
`The division between whatis high level protocol, and thus
`handled by the CPU processor, and what
`is low level
`protocol, and thus handled by the MAC processor, can vary
`greatly depending upon the intelligence level of the MAC
`processor.
`In a preferred embodiment,
`the infrastructure
`conforms to an industry standard wired LAN such as Eth-
`ernet. The MAC processor can be made very intelligent and
`therefore capable of handling a great deal of radio specific
`protocol. On the other hand, the MAC processor can be
`minimally intelligent and handle only the most basic pro-
`tocol functions allowing the CPU processor to handle the
`majority of the protocol functions.
`Utilizing multiple wireless adapters in a single access
`point, as well as incorporating independentintelligence and
`low level protocol responsibility into each wireless adapter,
`yields several significant advantages. The examples depicted
`in FIGS. 1-4 show access points using only two wireless
`adapters per access point. Utilizing two wireless adapters in
`the manner discussed below will greatly increase the reli-
`ability of a particular access point, as well as increase the
`reliability of the entire distribution network. Access points
`could use more than two wireless adapters and the utilization
`of the multiple wireless adapters would be similar to the
`implementation describes using only two wireless adapters
`with addition protocol being required to handle the increased
`redundancy and to allow for more sophisticated self moni-
`toring.
`the CPU processor 13 can
`to FIG. 1,
`Referring still
`designate the RF address to which each wireless adapter 15
`and 16 is to respond. The CPU processor 13 can, but need
`not, assign the same address to each wireless adapter.
`Therefore, in one configuration, the CPU processor 13 can
`designate that each of the wireless adapters 15 and 16
`respond to the address assigned to that access point 10.
`Designated as such, both radios 17 and 18 will be operating
`simultaneously on the same channel. In a frequency hopping
`system, both radios 17 and 18 would be operating on the
`same hopping sequence, and be mutually synchronized to
`that hopping sequence.
`Accordingly, the wireless adapters 15 and 16 are config-
`ured to receive incoming transmission from roaming com-
`puter devices within range. As both wireless adapters 15 and
`16 receive the transmission, each adapter can evaluate the
`quality information to the CPU processor 13. The CPU
`processor 13 uses the quality information to determine
`which wireless adapter is receiving the higher quality signal.
`The CPU processor 13 will then typically choose to receive
`the incoming transmission on the wireless adapter with the
`higher signal quality and respond using the same adapter.
`The antennas 21 and 22 can be positioned to allow the
`access point 10 to implement an antenna diversity scheme
`which will help reduce the negative effects caused by
`multipath interference. Antenna diversity can be accom-
`plished in various ways. For example, the antennas can be
`placed sufficiently far apart, typically greater than a quarter
`wavelength apart, or the antennas can be positioned at a 90
`degree angle with respect to each other to create a polar-
`ization antenna diversity scheme.
`With an antennadiversity schemein place, the signal from
`a wireless computer device will be received differently on
`each antenna due to multipath signal propagation. Therefore,
`each wireless adapter may receive a signal of a different
`quality. The CPU processor 13 can choose which wireless
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`adapter to use based upon the quality of the received signal.
`Each wireless adapter includes the capability of measuring
`signal quality and only good messageswill be forwarded on
`to the CPU processor 13. The quality can be appendedto the
`message or can be presented to the CPU in a memory
`register.
`Referring now to FIG. 2, another high reliability access
`point 20 built in accordance with the present invention is
`shown. In this embodiment, in addition to having an antenna
`diversity schemeat the access point level, there is an antenna
`diversity schemeat the wireless adapter level. Each wireless
`adapter 15 and 16 includesat least two antennas 21 and 23,
`22 and 24, respectively positioned to create an antenna
`diversity scheme. Thus for the wireless adapter 15 the
`antennas 21 and 23 are either positioned sufficiently far
`apart, more than a quarter wavelength, or the antennas 21
`and 23 are positioned in an asymmetrical or orthogonal
`manner to provide polarization diversity. The antennas 22
`and 24 for the wireless adapter 26 are placed in a similar
`manner.
`
`In this embodiment, an incoming signal is received on
`both antennas 21 and 23 of the wireless adapter 15. The
`MACprocessor 19 then determines the quality if the signal
`coming in on each of the antennas 21 and 23 connected to
`the wireless adapter 15. Based upon the signal quality
`information, the MAC processor 19 will choose whichof the
`antennas 21 and 23 to use to receive the incoming trans-
`mission. The MACprocessor will also forward the signal
`quality information regarding the selected antenna to the
`CPU processor 13. The wireless adapter 16 will perform a
`similar process and forward the signal quality information
`for its best antenna to the CPU processor 13. The CPU
`processor 13 can then determine which wireless adapter is
`receiving the highest quality signal and use that wireless
`adapter to receive the incoming transmission and respondto
`the transmitting station.
`Whena highreliability access point wishes to transmit a
`message, such as an acknowledgmentof a received message,
`to a roaming computer device, the CPU processor 13 will
`utilize the received quality signal information to determine
`which wireless adapter to use to send the message. Likewise,
`if the wireless adapter is utilizing an antenna diversity
`scheme it will also select the most appropriate antenna for
`transmitting a message.
`While one of the wireless adapters is transmitting, the
`other wireless adapter can operate as a promiscuouslistener
`to determine if the correct message is being sent. For
`example, referring to FIG. 1, if the CPU processor 13 is
`sending a message to a roaming computer device via wire-
`less adapter 16, wireless adapter 17 can operate in the
`receive mode and monitor the message being sent by the
`wireless adapter 16. This provides a local loop back capa-
`bility and allows the access point to perform self monitoring.
`If the CPU processor 13 determines that one of the wireless
`adapters is not operating correctly, the malfunctioning wire-
`less adapter can be disabled. Additionally, the CPU proces-
`sor 13 can then send a message to the system management
`portion of the host network via the infrastructure 26 that it
`has a defective wireless adapter and repairs are needed.
`Referring again to the configuration in which each of the
`wireless adapters is listening on the same channel, another
`advantage achieved by this configuration is the ability to
`receive two concurrent messages. In an access point that
`only contains one adapter, this situation will cause a colli-
`sion and neither message will be received. In a high reli-
`ability access point built in accordance with the present
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`invention, it is possible that the one wireless adapter will be
`able to receive one of the messages while the other wireless
`adapter receives the other, due to multipath fading at each of
`the wireless adapter antennas.
`Referring now to FIG. 3, a portion of a distribution
`network 30 utilizing high reliability access points is shown.
`The distribution network 30 includes an infrastructure 33
`and two high reliability access points 35 and 36. Access
`point 35 includes a CPU processor 37 and two wireless
`adapters 38 and 39. Access point 36 includes a CPU pro-
`cessor 41 and two wireless adapters 42 and 43. In the present
`example, a break 45 in the infrastructure 33 has occurred.
`Access point 35 is upstream to the break with respect to the
`host computer network and thus is not immediately affected
`by the break 45. However, access point 36 is downstream to
`the break 45 and therefore is no longer connected to the host
`computer network.
`Whena situation like this occurs, the downstream access
`point 36 will begin attempting to communicate with an
`upstream access point using wireless communication. In this
`example,
`the upstream access point
`is access point 35.
`However, the communication need not be with the access
`point immediately upstream, the only requirement is that it
`be with an access point which is upstream with respect to the
`break. The host computer networkor other access points will
`previously have shared the logistic and address information
`concerningall of the access points to each access point in the
`distribution network.
`
`Once communications with an upstream access point 35
`is established, each access point 35 and 36 will dedicate one
`of its wireless adapters 39 and 42, respectively to provide a
`wireless repair of the break 45 in the infrastructure 33. When
`this happens,
`the CPU processor for each of the access
`points will instruct the dedicated wireless adapter to change
`so that it is no longer operating on the same channel as the
`other adapter in the access point. A communication channel
`between access points is established. The dedicated wireless
`adapters 39 and 42 will no longer be used to transmit or
`receive information to or from roaming computer devices.
`However, the non dedicated wireless adapters 38 and 43 will
`communicate with the roaming computer devices. Once the
`top priority of re-establishing communications betweenall
`of the access points in the distribution network 30 and the
`host computer network has been accomplished, the access
`points can then send a message to the system management
`portion of the host computer network detailing where the
`break (or breaks) exists.
`It is conceivable that the distribution network could lose
`
`In this case, each of the high
`its entire infrastructure.
`reliability access points would dedicate one of its wireless
`adapters to network infrastructure communications while
`retaining one of its wireless adapters for communication
`with roaming computer devices. Using the same technique
`described above, a temporary or remote access point could
`be established that, intentionally, is not connected to the
`infrastructure. This configuration is discussed below in
`greater detail with reference to FIG. 5. The use of directional
`gain antennas for the dedicated wireless adapter would allow
`the temporary or remote access point to be positioned a
`considerable distance from the infrastructure.
`
`Referring now to FIG. 4, a high reliability access point 50
`with a backup power supply 52 is shown. Typically, the
`access point will be wires to an external power source 54
`such as a wall outlet. However, there is a great desire that if
`poweris lost that the distribution network not shut down
`since the roaming computer devices will normally not be
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`In this
`dependent upon the external power source 54.
`embodiment of the present invention, the back-up power
`source 52 is wired in parallel with respect to the external
`powersource 54. Thus, if the external power source 54 fails,
`the access point 50 will not lose power.
`Referring now to FIG. 5, a remote access point 70 is
`shown connecting to the infrastructure 33 by means of
`dedicated wireless adapters 62 and 72. The access point 70
`is not hard wired to th