CA2476866A1 - Wireless personal local area networks and power saving mechanisms therefor - Google Patents

Abstract

A transceiver apparatus (110) for creating a wireless personal local area network between a computer terminal (7) and one or more peripheral devices (9, 13, 23). A separate transceiver (110) is connected to the computer terminal (7) and to each peripheral device (9. 13, 23). The transceivers (110) can be connected to the terminal (7) or the peripheral devices (9, 13, 23) either internally or externally. A low power radio (112) is used to communicate information between the computer terminal (7) and the peripheral devices (9, 13, 23). Different transceivers (110) can be used for modifying the carrier frequency and power of the local area network. A microprocessor (120) is located inside each transceiver (110) and controls the information flow of the transceiver including the communication protocol which allows each device (7, 9, 13. 23) to know if other devices (7, 9, 13, 23) are communicating, which devices (7, 9, 13, 23) are being communicated to, and selectively address the peripheral devices (9, 13, 23). An Idle Sense communication protocol is used for information transfer between the computer terminal (7) and the peripheral devices (9, 13, 23).

Description

,.
TI~'LE: 'WIRELESS PERSONAL LOCAL AREA NETWORK
EAC1CGROtJND OF THE INDENTION
Computer terminals and peripheral devices ' are now used in practically every aspect of life. Computer terminals come in all shapes and sizes and vary greatly in terms of function;
power and speed. Additionally, the number of ~ .
peripheral devices which can be"attached to the computer terminals is incireasing. Many , peripheral devices exist such as printers, modems, graphics scanners, text scanners, code readers, magnetic card readers, external monitors, voice command interfaces, external storage devices, and so on.
Computer terminals and peripherals have become dramatically smaller and more portable.
Personal computers and peripherals are small enough to'~sit on the desk at work. Smaller still are lap top computers and notebook computers. There are computer terminals which are small enough to be mounted in a vehicle such as a delivery truck or on a fork lift. Still '' smaller are the hand field terminals typically used for their portability features where the user can carry the computes terminal in one hand and operate it with the other.
Despite the seduction in computer site, the computer terminal still must physically interface with the peripheral devices. Thus, there must either be a cable running from one of the computer terminals to each device or the computer terminal must be docked with the device while the information trans~fer.is to take place.
In the office or work'.place setting, the ~ .
physical connection is typically done with cables. These cables pose several problems. If w ~ ~ there are many peripheral devices, there isust be many cables attached to the,~~omputer terminal.
In addition to the eyesore~created by all of the cables, the placement,of the peripheral devices ' , is limited by.the~length, of the cable. Longer ' cables can be used but they are costly and do not~alleviate the eyesore created by having , cables: running in all directions., Additionally, there may be a limited numt~er of ports onvthe computer terminal thus limiting the number of peripherals that can be attached. , Another problem exists,when there are ~ several computer terminals which must share the same peripheral device such as a printer. All of the computers must be hardwired to the printer. As discussed above, long cables can fix this problem at least from a physical .
connection perspective but-there still remains a protocol problem between the different ' computers. This problem is especially severe when the various computers are of different types such as a mixed environment of IBM's and Macintoshes.
In the smaller computer terminal setting, the hand-held.terminals and the potables, the cabling and connection problem can be more .
severe and cumbersome. Peripheral devices such as printers and scanners of all types have been reduced dramatically in size to match the smallness of the computer terminals. A notebook computer operator may wish to carry the computer _3_ and a cellular phone modem., in a briefcase.
Similarly, an operator may 'wish to,have a hand-held computer terminal in one hand,~a small portable printer attached~t~o his belt. and a .

'h~nd. The smallness of code reader in the other the computers and peripherals~makes these demands possible but the required cabling makes these demands costlya inconvenient and even dangerous. .', ' 10 Physically connecting the computer terminals and peripherals severely reduces the efficiency gained by making the units smaller.

An operator must somehow account for all of the ,', devices in a system and keep them all connected.

This can be very invonveient. In the.notebook w computer and modem example;; the operator may wish to have freedom to move around with the ' computer but without the modem. He may, for example, wish to work in various locations on a job sight and at various times transmit o~

receive information via his modem. If the modem and the computer are hard wired together, he must either carry the modem with him at all times or connect it and then disconnect it each time he wishes to use the modem:. Similarly, the operator of the hand held terminal, code reader and printer will have the feeling of being all tied~up while using the three devices simultaneously when all three devices are connected with cables.

The physical connections created by cabling can be expensive because cables frequently prove to be unreliable and must be replaced frequently. In portable environments, cables are subject to frequent handling, temperature extremes, dropping and other physical trauma. It is not uncommon for the F.
. -4-,,.
devices to need replacing every three months~or so. Additionally, alh of tie cabling can be dangerous. An operator whQ is using, holding or carrying.several devices and feels all tied ug is not just inconvenienced, he may be~severely limited in his mobility and flexibility as he moves about the work area. This loss of ' mobility and flexibility directly undercuts. the entire reason for having small and portable computers and peripheral de'rices and greatly w increases the'likelihood'of operator injury while usingv the computer and.peripheral devices.
Furthermore, as the cables wear out and break, which, as mentioned" happens frequently, .
~ there are dangers which are' associated with the electrical current running through~the cables.
If the cable or connectors. break, the current, could shock the operator or'create a spark which could cause a fire or even an explosion in-some work environments.
. Attempts to alleviate or eliminate these . problems have been made but have not been greatly successful. One solution is to .
incorporate a computer terminal and all of the . peripherals into one unit: However, this solution proves unsatisfactory for several reasons. For example. the incorporation of many devices into one unit greatly increases the size and weight, thus jeopardizing the portability of the unit. Furthermore, incorporating all of the functions into one unit greatly reduces and, in mast cases eliminates, the flexibility of the overall system. A user may only wish to use a hand-held computer terminal at times, but at other times may also need to use a printer or occasionally a code reader. An all-incorporated unit thus becomes either overly large because it must include everything, or very limiting because it does not include,evezyth3ng.
Another solution has been to set up Local Area Networks (LAN's) utilizing various forms of RF (Radio Frequency) communication. The LAN's to date, however, have been designed for large scale wireless communications between several portable camputer terminals and a host computer.
Therein, the host computer., ~.tself generally a stationary device, manages a~series of 10~ stationary peripherals that, upon requests to the host, may be utilized by the portable terminals. Other large scale~'wireless , communications have also-be.en developed which are ,' for RF communication between. several computer ~ terminals and peripheral d~arices, but all proving to be ineffective~as a solution.' For 'example, these systems sequi~,e the peripheral devices to remain active at, all times to histe~n for. an occasional communication. Although.this requirement may be acceptable~for stationary peripheral devices receiving virtually unlimited power (i.e., when plugged into an AC outlet), it proves detrimental to portable peripherals by unnecessarily draining battery power.
Similarly, in such systems, the. computer terminals are also required to remain active to receive, an occasional communication not only _ from the other terminals or the host but also from the peripherals. Again, often unnecessarily, battery power is wasted.
In addition, such large scale systems are designed for long range RF communication and often require either a licensed frequency or must be operated using spread spectrum technology. Thus, these radios are typically cost prohibitive, prove too Iarge for convenient use with personal computers and small peripheral devices, and require a great deal of 73164-12$D
' _6_ transmission energy utilization.
. Thus, there is a need-for a radio frequency communication network that' supports the,use of . network peripherals which~solves the foregoing problems relating to power conservation and portability.
. SAY OF T8E INVENTION
The present invention solves many of the problems inherent in the prior art radio frequency communication network. The mobile network device, .. 10 participates as a slave to the first network pursuant to the first protocol and as a master to the second. network pursuant to the second protocol, and resolves conflicts between tb~
. ~ first and second protocols in communication 15 systems having devices which use battery power.
The present invention rel~a'tes generally to local area networks and, more specifically. to a ' . , communication system for maintaining connectivity between devices on networks~which 20 ~ have different operating parameters while limiting the power drain of 'battery po~zered devices.
In one embodiment of the present invention, a mobile network device has a single radio unit 25 which is capable of participating in a first and second radio network which operate using a first and second communication protocol. The mobile network device participates as a slave to the .
first network pursuant to the first protocol and 30 as a master to the second network pursuant~ta the second protocol, and resolves conflicts between the first and second protocols.
In another embodiment of the present invention, a mobile network device has a first 35~ radio transceiver for communicating with a main radio network and a second radio transceiver for communicating with a radio subnetwork. The -'7 -mobile network device participates as a slave to the main , radio network and' participates ~as a master to the radio subnetwork.
In a further embodiment of the present .
invention, a mobile netwob~~k~,device has a single radio unit capable~of participating in a first and a second radio network. The.first and second radio networks operate using a first. and second communication protocol,; respectively:
ZO The mobile network device participates as a slave to the first network pursuant to the first protocol and as a master to the seFond network pursuant to the second protocol and enters,a state of low power consumption when not communicating with either the first or second netvuork. ~ .
In another,embodiment;.of the present -invention, an RF local area network contains a first network device which 'uses battery power to transmit data to a second network device.. In order to conserve power, the second network device determines a range value-betweew °the first and second network devices and transmits that value to~the first network device so that the first network device can identify an appropriate, and potentially lower, data rate for subsequent transmission of data. The first network device may also consider its own battery parameters along with the received range value and identify an appropriate power level as well as data rate for subsequent transmissions.
In another similar embodiment, the second network device. determines the range value between the first and second network devices and, based on the range value, indicates to the first network device an appropriate, and potentially lower, data rate for subsequent data transmission to the second network device. The second network device may also consider'battery _g_ parameter information received from the first network device .a and use that information along,with the range value to indicate to the first network device an appropriate power level, as well as data rate, for subsequent transmissions by the first network device.
;; Thus, according to an aspect of the, invention, there is provided a communication system comprising: ,a first radio network operating using a first communication protocol; a second radio network operating using a second ' communication protocol; a mobile network device having a single radio unit capable of participating in both the first and second radio networks; the mobile network device v.
participating as a slave device to the first radio network pursuant to the first communication protocol while participating as a master device to the second radio network pursuant to the second communication protocol; and the mobile network device resolving conflicts between the first and second communication protocols.
The invention provides, in a further aspect, a communication system comprising: a main radio network; a radio subnetwork; a mobile network device having a first radio transceiver for communicating with the main radio network and a second radio transceiver for communicating with the radio subnetwork; the mobile network device participating as a slave device to the main radio network while participating as a master device to the radio subnetwork.
The invention also provided a communication system comprising: a first radio network operating using a first communication protocol; a second radio network operating using a second communication protocol; mobile network device -8a-having a single radio unit capable of participating in both the first and second radio networks; the mobile, network device participating as a slave device to the first radio network pursuant to the first communication prdtocol while participating as a master device to the second radio network pursuant to the second communication protocol; and the mobile network device entering a state of low power consumption when not communicating with either the first or the second~radio network.
In accordance with a still_further aspect of the invention, there is provided a communication system comprising: a first radio network comprising a first .
plurality of network devices; a second,radio network ' ., comprising a second plurality of network devices; a mobile network device configured to participate as a member of both the first and second pluralities of network devices; when .
within range of one of the second plurality of network devices, the mobile network device participates as a, master device in the second radio network; and when within range of one of the first plurality of network devices, the mobile network device participates as a slave device in the first radio network; the second plurality of network devices entering a state of low power consumption when communication with the. mobile network device is not available.
According to another aspect of the invention, there is provided a communication system comprising: a first radio network comprising a first plurality of network devices; a second radio network comprising a second plurality of network devices; a mobile network device configured to participate as a member of both the first and second pluralities of network devices; when within range of one of the second plurality of network devices, the mobile network device participates as a master device in the second radio network; and when within -8b-range of one of the first plurality of network devices, the mobile network device participates as ~a slave device in the first radio network. , BRIEF DESCRIPTION OF THE DRAWINGS
Fig. la illustrates a warehouse environment incorporating a communication network which maintains communication connectivity between the various network'devices according to the present invention.
Fig. lb illustrates other features of the present invention in the use of a mobile vehicle and an associated microLAN network which is capable of detaching from the main communication network when moving out ,of range of the main network to perform a service, and reattaching to the main network when moving within range to automatically report Qn the services rendered.
Fig. 2 is a diagrammatic illustration of the use of a microLAN supporting roaming data collection by an operator according to the present invention.
Fig. 3 is a block diagram illustrating the functionality of RF transceivers built in accordance with the present invention.
Fig. 4 is a diagrammatic illustration of an alternate embodiment of the personal microLAN shown in Fig. 2.
Fig. 5 is a block diagram illustrating a channel access algorithm used by microLAN slave devices' according to the present invention.
Fig. 6a is a timing diagram of the protocol used according to the present invention illustrating a typical communication exchange between a microLAN master device having .. 9 ..
w virtually unlimited power resources and a v microLAN slave device. '~'~' Fig. 6b"is a timing diagram of the protocol used according to the present invention illustrating a typical communication exchange between a microLAN master device having limited power resources and a microLAN,'slave device.
' . Fig. 6c is also a timing diagram of~'the protocol used which illustrates a scenario , l0 wherein the microLAN master device fails to , service microLAN slave devices 'Fig. 7 i.s a timing diagram illustrating the microLAN master device's servicing of both~the high powered main communication network and,the, , low powered microLAN subnetwork, with.a single or plural radio transceivers, in accordance with .
the present invention.
t Figs. 8 and 9 are block diagrams , illustrating additional powez saving features according to the present invention wherein ranging and battery parameters, are used, t;,o , optimally select the appropriate data rate and power level of subsequent transmissions.
DETAILED DESCRIPTION OI9' THE INVENTION
Fig. la illustrates a warehouse environment incorporating a communication network which maintains communication connectivity between. the various network devices according to the present invention. Specifically, a worker utilizes a computer terminal 7 and a code reader 9 to collect data such as identifying numbers or codes on warehoused goods, such as the box iC.
As the numbers and codes are collected, they are forwarded through the network to a host computer 11 for storage and cross-referencing. In addition, the host computer 11 may, for example, forward cross-referenced information relating to ~s ~1~_ the collected numbers or~cddes backthrough the .
network for',display on the.terminal~ 7 or for printing on a printer 13. 'Similarly, the , collected may be printed.ftom the computer .
terminal 7 directly to the printer 13. Other exemplary communication pathv~ays supported by the present invention include messages exchanged between the computer terminal ~ and other , computer terminals (not shown) or the host.
. ~. 10 computer 11. . , ' , Many of.the dev,ices.found in the illustrative netwo=k are battery powered and , therefore must conservatively utilize their radio transceivers. For example, the hand-held , computer terminal 7 receiu~s its.power.~from ~ , . either an enclosed battery or a forklift. battery (not shown) wia a docking' ~st~ation within the forklift 14. Similarly, the code .reader. 9 operates an portable battery power as may the printer 13. The arrangement of the .
communication network, communication protocols used, and data rate and power level adjustments help to optimize battery conservation without substantially degrading network performance.
The overall communication network of the present invention is arranged into two functional groups: l~~a main communication.
network; and 2) a microLAN network. The main communication network in the illustrated warehouse embodiment includes a hard-wired backbone LAN 19 and base stations 15 and 17. A
host computer 11 and any other non-mobile network device located in the vicinity of the backbone LAN 19 can be directly attached to the backbone LAN 1°. However, mobile devices and remotely located devices must maintain connectivity to the backbone LAN 19 through either a single base station such as the base station 15, or through a mufti-hop network of .. base stations such as is~'illustrated by th~,base stations 15°and 17'. The base stations 15 and 17 contain a higher power transmitter, and provide coverage over the entire~~warehouse floor.
. Although a single base station may be sufficient, if the warehouse i's too large or contains interfering physical barriers,'the mufti-hop plurality of base,stations l7 may be necessary. Otherwise, the~backbone LAN 19 must be extended to connect all of the base stations ~.
~. 17 directly.to provide sufficient radio coverage. Through'the main communication network, relatively stable.,~.long range. wireless ' 15 and hard-wired communicat.i~on is maint~ined.~
' ~ . . Network devices that,; are mobile or remote (i.e., cannot be directlyconnected to the backbone LAN 19 ) are fitted ~urith RF
transceivers. To guarantee that such a network device will be able to directly communicate with at.least one of the base stations 15 and 17, the fifted transceiver is selected to yield.
approximately the same transmission power as do the base stations 15 and 17. However, not all mobile or remote network devices require a direct RF link to the base stations 15 and 17, and some may not require any link at all.
Instead, communication is~~generally localized to a small area and, as such, only requires relatively lower power, short range transceivers. The devices which participate in the localized, short range communication, form what is termed herein a "microLAN".. For example, the interaction between peripheral devices such as the printer 13, modem 23, and code reader 9 with the terminal 7 provide a, justification for a microLAN configuration.
For example, the printer 13 may be located ., -12- , , , in a dock with the sole assignment of printing out forms based on the code"information gathered ~.
from boxes delivered to the dock. 'In such an example, only when the forklift 14 enters the ,, .
S dock area should the prin'~e~~; 13 begin printing the collected code information. Within the dock area, communicating via the base stations 15 and 1? with the required high powered transceivers is avoided by establishing a microLAN on the ~ .
dock. Specifically, instead,of the high powered .
~~transceivers for communicating with the main' , communication network', ~the,printer 13 is fitted ~ .
with a low power microLAN~transceiver for short , range' communication.direct~ly to the computer terminal ? in the forklift 14. The. computer', terminal 7 is also fitted,with a transceiver ~, capable of.direct, low power communication with the printer 13. Thus, when, within microLAN.
radio range of the printer l3, the cvmputei ~ , .terminal ? transmits the code information at a relatively low power level to the printer. 13.
Whiles in range !whether printing or not)~,~ the computer terminal 7 and printer 13 together participate in a low power, microLAN network.
In the previous example., no communication was necessary between the .microLAN devices and the main network. However, other microLAN
configurations require at least some access to the main network. For example, because of battery constraints, the code reader 9 is also fitted with a microLAN transceiver. whenever the code reader 9 is used, collected code ' signals and counterpart information are not directly exchanged with the host computer 11 via the main network. Instead, in the illustrated example, the computer terminal 7 is configured to be able to communicate not only within the microLAN but also through the main connection .

network. This is accomplished by fitting the computer terminal 7 with~~~~a transceiver (s) capable of communicating ~on both networks (see discussion related to Fic~.'. 3 below). Thus. to w s.

, reach the host computer T'1; the code reader 9 first transmits to the computer terminal 7 via the microhAN. i,.e., through tie microLAN

transceivers in each device. Upon receipt of the data, the computer terminal 7 relays the information to one of the. 'base stations. 15 and ' ' 17 for forwarding to,the host 11. Communication' from the host il to the .code reader 9 is accomplished via. the same pathway.

It is also possible for any two devices in the microT..AN network to communicate to each other. For example, the~.modem 23 could receive data and directly transmit it to the printer 13 r for printing. Similarly: the code reader 9 might choose to directly communicate code ~ signals to other network devices via the modem 23.

In an alternate configuration. a microLAN' base station 21 is provided which may be directly connected to the backbone.LAN,19 (as shown) or indirectly connected via the base stations 15 and 17. The microLAN base station 21 is positioned in the vicinity of other microL~AN network devices and thereafter becomes a participant. Thus, microLAN communication 3o flowing t~ or from the main communication network avoids high power radio transmissions altogether. However, it can be appreciated that a stationary microLAN base station may not always be an option when all of the microLAN

participants are mobile. In such cases, a high power transmission to reach the main communication network may be rea_uired.

As briefly described above, in any _l4_ 'microLAN, the participating ''devices ~ (!'microLl~N
devices") need not all possess the transceiver capability to reach the main communication network. However, at least'one microLAN device. , needs to have that capability to maintain overall network connectivity. , w ' Fig. lb illustrates other features.o~ the present invention in the use, of a mobile vehicle and an associated microLAN neework~which is l0 capable of detaching from the main communication network when moving out of :range of the main network to perform a service, and reattaching to , the main network when moving.within range to. .
'. automatically report on the serviees randered:.
Tn particular, like the forklift l4yof Fig. la, a delivery truck 33 provides a focal point for microLAN aceeas. Within the Ftruck 33, a storage terminal 31 is docked so as'~o draw power from the truck 33's battery supply. The storage terminal 31 is configured with a microLAN
transceiver. Similarly, a computer terminal.~~
also configured as a microLAN.device may either be docked or ported. Because of greater battery access and because of the amount of data to transfer, the storage terminal 31 is also configured to communicate with the main communication network. ~ , Prior to making a delivery, the truck enters a docking area for loading. As goods are loaded into the truck, the driver enters information regarding each loaded good into the storage terminal 31 via either the terminal 7 or .
the code reader 9 (Fig. ia) using the microLAN
network communications. This loading might also be accomplished automatically as the forkli=~ ~4 comes into range of the delivery truck 31, joins the microLAN network, and transmits the previously collected data as described in 0 3;
_ relation to dig la. In addition, as information . .~.,,,, w regarding a good is received and stored, the, storage device might also request further information regarding any,br all of the goods .
via the microLRN's link to~~the host computer li: .
through the main communication network.
." Specifically, the microLAN base"station 21 if located on the dock could provide a direct~low power microLAN connection t~o,the backbone LAN 19 and to the host computer 11: Otherwise, because , of~the normal data f low pathway and because- of ~ .
its.greatest. access to available power, the storage terminal 3l~is configured with a transceiver capable of communicating with the main 'communication network via the base stations . ~., 15 and 17. When fully loa~~d and prior to .
leaving the dock, the storage device 31 communicates via the microLAN to the printer 13 to generate a printout of information~relating.
to the loaded goods. In addition, the information is transmitted via the microLAN to the modem 23 for relay to a given destination site. Upon reaching the destination, the storage terminal 31 detects and participates in 2S the microLAN of the delivery site dock. As specific goads are unloaded, they are scanned for delivery verification, preventing delivery of unwanted goods. The driver is also informed if goods that should have been delivered are still in the truck. As this process takes place, a report might also be generated via.a microLAN printer on the destination dock for signature. Similarly, a microLAN modem on the destination dock might relay the delivery information back to the host computer il for billing information.
Simiiariy, if the truck 33 is used for service purposes, the truck 33 leaves the dock ., , -1&-in the morning with the addresses and directions of the serviee destinations,,] teehni~al manuals, and service notes which have been selectively downloaded from the host computer via the main .
~~, 5 network and microLAN to t~e'''storage terminal 31.
Upon pulling out of range of'~the microLAN
network in the dock, the storage terminal 31 and the computer terminal 7 automatieally form. an independent, detached microLAN. At each service _ , , address, the driver collects'information using ' .
the terminal 7 either as the data is collected ~ , .
if within microLAN transmission range of the storage terminal 3I,, or~as soon as the terminal ,' .7 comes within range. Through the detached microLAN network such information is available a , ~~ on the computer terminal. ~vupon returning to the ., dock, as soon as the independent microLAN formed between the storage terminal °31 and the computer terminal 7 come within microLAN range of the microLAN devices on the dock, the detached.
microLAN automatically merges with the~do'ck's microLAN (becomes "attached"), and the storage terminal 31 automatically transfers the service ' information to the host eomputer li whieh uses the information for billing and in formulating the service destinations which will be automatically downloaded the~next day.
Eig. 2 is a diagrammatic illustration of , another embodiment using a microhAN to supporting roaming data collection by an operator according to the present invention. As an operator ~1 roams the warehouse floor he carries with him a microLAN comprising the terminal 7, code reader 9 and a portable printer 3S 58. The operator collects information regarding goods, such as the box 10, with the code reader 9 and the terminal 7. If the power resources are equal, the terminal 7 may be designated to -1?-also communicate with the m~.in communication 'network. Specifically, corresponding information'to the code data must be retrieved from the host computer 11,~,,lcollected code information and retrieved~'corresponding " , information needs to be displayed on the ' terminal ?, and, after viewing'for verification, the information needs to be:printed on the printer 58 . ~ Because of this 'data flow requirement, the computer terminal 7 is selected as the microLAN device.which must also carry the responsibility of communicating with the main communication network.
If during collection; the operator decides, to power down the computer terminal 7..because it is not needed, the microLAN~network becomes detached from the main communication network.
' ~ Although it might be, possible for the detached microLAN to function, all co~munica~tion with the host computer 11 through the main communication network is placed in a queue awaiting ~.
reattachment. As soon as the detached microLAN
cones within range of an attached microLAN
device, i.e., a device attached to the main network, the queued communications are relayed to the host.
To avoid detachment when the terminal 7 is powered down, the code reader 9 may be designated as a backup to the terminal 7 for performing the higher power communication to the main communication network. As described in more detail below in reference to Fig. 6c w regarding the idle sense protocol,..whenever the code reader 9 determines that the terminal 7 has stopped providing access to the main communication network, the code reader 9 will take over the role if it is next in line to perform the backup service. Thereafter, when r .~ ,the,computer terminal '7 is powered up; it monitors the~microLAN channel, requests and . regains from the code reader 9 the role of providing an interface with~,the main computer network. This, however, does 'not restrict the code reader 9 from accessing tie main computer network although the reader'~,may choose, to use the computer terminal 7 for~~power conservation reasons.
. , Ire addition, if the computery terminal 7 , reaches a predetermined low battery threshold level, the termanal~7 will- attempt to pass the burden of providing main network access to other microLAN backup devices. .If no backup devicew , exists in the current mierohAN, the.compu~er ,terminal ~ may refuse all high power transmissions to the main communication network.
Alternatively, the. computer terminal 7 msyw either refuse predetermined select types of requests, or prompt the operator before performing any transmission to the main network.
However, the computer terminal 7 may still listen to the communications from the main communication network and inform microLAN
members of waiting messages,e Fig. 3 is a block diagram illustrating the functionality of RF transceivers built in accordance with the present invention. Although preferably plugging into PCMCIA slots of the computer terminals and peripherals, the transceiver 110 may also be built-in or externally attached via available serial, parallel or ethernet connectors for example.
Although the transceivers used by potential microLAN master devices may vary from those used by microLAN slave devices (as detailed below), they all contain the illustrated functional blocks.

_19_ In particular,' the transceiver Z10 contains a radio unit 112 whieh.attaches to an attached antenna I13.~ The radio unit 112 used in ' microLAN slave devices need~only provide reliable loci power transmi~ssaons, and are w designed to conserve cost,. weight and size.
... wPotential microLAN master devices not only require the ability to communicate with microLAN
slave devices, but also require higher poweic radios to also communicate~With the main network. Thus,.potential microLAN master w, .
devices and other non-microLAN slave devices might contain two radio units 112 ~(or two transceivers 110) -- one serving the main w network and the other serving the microLAriT
network -- else only conta',ii~ a single radio unit to service both networks.~~
In embodiments where c~~t and addational~
weight is not an issue, a~dual radio unit configuration for potential microLAN master devices provides several advantages. For example, simultaneous transceiver operation is possible by choosing a different operating band for each radio. In such embodiments, a 2.4GHz radio is included for main network communication while a 27MHz radio supports the microLAN
network. MicroLAN slave devices receive only the 2'7NiHa radio, while the non-potential microhAN participants from the main network are fitted with only the 2.4GHz radios. Potential microLAN master devices receive both radios.
The low power.27 MHz microLAN radio is capable of reliably transferring information at a rance of approximately 40 to 100 feet asynchronously at 19.2K BPS. An additional benefit of using the 27 MHz frequency is that it is an unlicensed frequency band. The 2.4GHz radio provides sufficient power (up to 1 Watt) to communicate with other main network devices. Many different frequency. choices could also be made'such as the' 900MHz band, etc.
In embodiments where cpst and additional weight are at issue, a single radio unit , .
configuration is used for potential microLAN
master devices. Specifically, ih such embodiments, a dual mode 2.4GHz radio supports both the microLAN and main networks: In.a microLAN mode, the 2.4GHz radio operates at a low power level tsub-milliwatt) to support microLAN communication at relatively close distances t20-30 feet). In a high power fup~ to 1 Watt) or main mode, the 2.4GHz radio provides relatively long distance communication . , ' connectivity with the main,~n'etwork. Although . all network devices might be fitted with Such a dual mode radio, only microf~AN master devices use both modes. MicroLAN slave devices would only'use the low power mode while all other main network devices would use only~the high~power-mode. Because of this, to save cost, microLAN , slave devices are fitted with a single mode radio operating in the microLAN mode. Non-microLAN participants are also fitted with a single mode imain mode) radio unit for cost savings.
Connected between the radio unit 112 and an' interface 110, a microprocessor 120 controls the information flow between through the transceiver 110. Specifically, the interface 115 connects the transceiver 110 to a selected computer terminal, a peripheral device or other network device. Many different interfaces 115 are used and the choice will depend upon the connection port of the device to which the transceiver 110 will be attached. Virtually any type of interface lI0 could be adapted for use with the _21-transceiver 110 of the present invention.
_~ Common industry interface°st~~andards include RS-232, RS-422-, RS-485, lOHASE: Etherne~t, lOBASES
Ethernet, lOBASE-T Ethernet:~ fiber optics, IBM
4/16 Token Ring, V.11, V.24~;, V.35, Apple Localtalk and telephone interfaces. In addition, via the interface 115, the ' microprocessor 120 maintains a radio independent, interface protocol.with,the l0 attached network device, isolating the attached ~, device from the variations in radios being used.
The microprocessor 120 alto controls the radio unit 112 to .accommodate communication with , either the main network (for main mode ;
radios), the microLAN (for microLAN radios.),' or ,, both (for dual mode radios)~:~ More specifically, ,~
in a main mode transceiver,' the microprocessor 120 utilizes a'main protocol~~rto communicate with the main network. Similarly, in a microLAN mode transceiver, the microprocessor 120 operates pursuant to a microLAN protocol to communicate in the microLAN network. In the dual mode transceiver, the microprocessor 120 manages the use of and potential conflicts between both the main and microLAN protocols: Detail regarding the main and microLAN protocols can be found in reference to Figs. 6-9 below.
In'addition, as directed by the .
corresponding communication protocol, the microprocessor 120.controls the power consumption of the radio 112,.itself and the interface 115 for power conservation. This is accomplished in two ways. First, the microLAN
and main protocols are designed to provide for a 3~ low power mode or sleep mode during periods when no communication involving the subject.
transmitter is desired as described below in relation to FIGS. 6-7. Second, both protocols r are designed to adapt in bpth data rate and ,, transmission power based, on power supply. (i.e., battery) parameters and range information as described in reference to Figs. 8-9.
In order to insure that the proper device' is receiving the information transmitted, each w device is assigned a unique address.
Specifically, the transceiver 110 can either have a unique address of 'its own or .can use' r.he unique address of the device to which it is attached. The unique address of the transceiver canveither be one selected by the operator or system designer or one which is permanently assigned at the factory such as an IEEE addiess.
The address 121 of the particular transceiver 110 is stored with the m~.croprocessor.12~0.
In the illustrated embodiments of Figs. 1-2, the microLAN master device is shown as be~n~g either a microLAN base station or a mobile or portable computer terminal. From a data flow viewpoint in considering the fastest access.
through the network, such choices for the microLAN master devices appear aptimal:
However, any microLAN device might be assigned the role of the master, even those that do not seem to provide an optimal data flow pathway but may provide for optimal battery usage. F~r example, in the personal microLAN network of Fig. 2, because of the support from the belt 59, the printer might contain the greatest battery capacity of the personal microLAN devices. As such, the printer might be designated the microLAN master device and be fitted with either a dual mode radio or two radios as master devices require. The printer, or other microLAN
slave devices, might also be fitted with such required radios to serve only as a micraLAN
master backup. If the battery power on the actual microLAN.master, i.e;. the hand-held terminal 7 (Fig. 2), drops ,below a preset .
threshold, the backup master takes over.
Fig. 4 is a drawing,w~ich illustrates an ' embodiment of the personal~~microLAN shown in Fig. 2 which designates a printer as the microLAN master device. Specifically, in a personal microLAN network~165, a computer terminal 170 is strapped to,,the forearm of the operator. A code reader 1'7i straps~to the back ' of the hand of the user and is triggered by .
pressing a btitt,on 173 With the'thumb. Because of their relatively low battery energy, the computer terminal 170 and~code reader 171 are designated microLAN slave devices and each . contains a microLAN transceiver having a broadcast range of two meters or less. Because of its greater battery enes~gy, the printer 172' contains a dual mode radio,and ~s designated the microLAN master device.
.~v Fig. 5 is a block diagram illustrating a w channel access algorithm used by microhAN slave devices according to the present invention.
At a block 181. when a slave device has a message to send, it waits~for an idle sense message to be received from the microLAN master device~at a block 183. When an idle sense message is received, the slave device executes a back-off protocol at a block 187 in an attempt to avoid collisions with other slave devices waiting to transmit. Basically, instead of permitting. every slave device from repeatedly transmitting immediately after an idle sense message is received, each waiting slave is required to first wait for a pseudo-random time period before attempting a transmission. The pseudo-random back-off time period is generated and the waiting takes place at a block 187. At -24-.
a block 189, the channel is, sensed to determine . , ., whether it is clear far transmission. If not, a branch is made back to the block 183 to attempt a transmission upon receipt of the next idle ,, sense message. If the chahnel is still clear, at a block 191, a relatively small "request to send" type packet is transmitted indicating the desire to send a message. ,If no responsive °'clear to send'° type message is received from , the master device, the slave device assumes that a collision occurred at a block 193 and branches back to the block 183 to try,again. If the "clear to send" message is,received, the slave ,'' device transmits the message at a block 195., , Several alternate channel access strategies have been developed for carrier sense multiple access (CSMA) systems and include i-persistent, non-persistent and p-persistent: Such strategies or variations thereof could easily be adapted to work with the present invention:
Fig. 6a is'a timing diagram of the~..protocol used according to the present invention , illustrating a typical communication exchange between a microLAN master device having virtually unlimited power resources and a microLAN slave device. Time line 201 represents communication activity by the microLAN master device while time line 203 represents the corresponding activity by the microLAN slave device. The master periodically transmits an idle sense message 205 indicating that it is available for communication or that it has data for transmission to a slave device. Hecause the master has virtually unlimited power resources, it "stays awake" for the entire time period 2C
between the idle sense messages 205. In othe:
words, the master does not enter a power conserving made during the time periods 207.

r The slave device uses a binding protocol ' '.(discussed below with reg~rd~ to Fig., 6c) to synchronize to the master~device so that the slave may enter a power conserving mode and 5 still monitor the idle sense, messages of the master to determine if the'master requires servicing. For example, referring to Fig. 6a;
the slave device monitors an idle sense message of the master during a time period 209, to determines that no servicing:is required, and enters a power conserving mode during the time , peribd 211. The slave then activates during a .
time period 213 to monitor the~next idle sense message of the master. Again, the slave determines that no servicing is,required and ~ .
. .
enters a power conserving mode during a,time period 215. When the slave'activates again during a time period 217 to monitor~the next idle sense message, it determines from a "request to send" type message from the~master that the master has data for tr~nsmission,.to.the slave. The slave responds by sending a "clear to .send" type message during the time period 217 and stays activated in order to receive transmission of the data. The master is thus able to transmit the data to the slave during a time period 219. Once the data is received by the slave at the end of the time period 221, the slave again enters a power conserving mode .
during a time period 223 and activates again during the time period 225 to. monitor the next idle sense message.
Alternatively, the slave may have data for transfer to the master. If so, the slave indicates as such to the master by transmitting a message during the time period 217 and then executes a backoff algorithm to 'determine haw long it must wait before transmitting the data.

"f~
- 2 6 -,,, ~ . .
The slave determines from~~the backoff algorithm that it must wait the time:~period 22'7 before transmitting the data during the time period 221. The slave devices use the backoff algorithm in an attempt to~avoi,d the collision w of data, with that from other s~.ave, devices which are also trying to communicate with the master.
The backoff algorithm is~discussed more fully above in reference to~Fig. 5.
,The idle sense messages of the master may also aid in scheduling cocrimunication between two slave devices. For example, if a~first slave device has data for transfer to a second slave ~.
device, the first slave sends a messa~ge~to the master during the time period 209. requesting communication with the second slave. The master then broadcasts the request during the next idle sense message. Because the second slave.~is monitoring the idle sense message, the second slave receives. the request and stays activated at the end of the idle sense message in order to receive the communication. Likewise, because the first slave is also monitoring the idle sense message, it too receives the request and stays activated during the time period 215 to send the communication.
Fig. 6b is a timing diagram, of the protocol used according to the~present invention illustrating a typical communication exchange between a microLAN master having limited power resources and a microLAN slave device. This exchange is similar to that illustrated in Fig.
6a except that,-because it has limited power resources, the master enters a_power conserving mode. Before transmitting an idle sense message, the master listens to determine if the channel is idle. If the channel is idle, the master transmits an idle sense message 2~5 and then Waits a time period 23T~ to determine,if~any.
. , ..
devices desire communication. If no', communication is desired,~tl~e master enters a power conserving mode during a time period 233 a before activating again to fis;ten to the . channel. If the channel is not idle, the master does not send the idle sense. message and enters a power saving mode for a time period 235 before activating again to listen ton~the channel.
. 10 Communication between the master and slave '' devices is the same as .that discussed above in . ', reference to Fig 6a except that, after sending or receiving data during the, time period 219, the master device enters a power conserving~mode ' during the time period 237.,.
Fig. 6c is ~ also a t~:~miag diagram of the protocol used which illustra~,.es~a seenario wherein the microLAN master.devi.ce fails to service microLAN slave devices. The master device periodically sends an idle sense message 205,, waits a time period 231 a and enters 'a power conserving mode during a time period 233 as discussed above in reference to Fig 6b.
Similarly, the slave device monitors the idle ' sense messages during tame periods 209 and 213 .and enters a power conserving mode during time periods,211 and 215. For some reason, however, the master stops transmitting idle,sense messages. Such a situation may occur, for example, if the master device is portable and is carried outside the range of the slave's radio.
During a time period 241, the slave unsuccessfully attempts to monitor~an idle sense message. The slave then goes to sleep for a time period 243 and activates to attempt to monitor a next idle sense message during a time period 245, but is again unsuccessful.
The slave device thereafter initiates a binding protocol to attempt.,"to regain synchronization with the master. Y~hile two time periods t24I, and 245) are shown, the slave may .
,.
initiate such a protocol after any number of unsuccessful attempts to locate an idle sense message. With this protocol, the slave stays active for a time period Z47,.which. is equal to the time period from one idle sense message, to ' the next, in an attempt to,locate a next~idle ~_10 sense message. If the slave is again unsuccessful, it~may stay active until it y .
locates an idle sense message'from the master, or, if power consumption is a concern, the slave may enter a power conserving mode at the end~of z5 the time period 247 and activate at a later time ,.
. to monitor for an idle sense message.
In the event the master device remains outside the range of the slave devices iw the microLAN network for a period long enough such 20 that communication is hindered, one of the slave devices may take over the functionality.'of the master device. Such a situation is useful when the slave devices need to communicate with each other in the absence of the master. Preferably.
25 such a backup device has the ability to communicate with devices on the main communication network. If the original master returns, it listens to the channel to determine idle sense messages from the backup, indicates 30 to the backup that it has returned and then begins idle sense transmissions when it reestablishes dominance over the microLAN
network. . ' Fig. 7 is a timing diagram illustrating the .
35 microLAN master device's servicing of both the high powered main communication network and the low powered microLAN subnetwork, with a single or plural radio transceivers, in accordance with the d nr present invention. Block.,,251 represents typical communication activity of the master device. Line 253 illustrates the master's communication With a base'~Station on the main communication network while'l~ine 255 illustrates the master's communication with a slave device on the microLAN network. Lines 257 and 259 illustrate corresponding communication by the base station and slave device, respectively.
la The base station periodically broadcasts HELLO messages 261 indicating that it is available for. communication. 'The master device monitors the HELLO messages~,during a time period 263, and, upon determining that the base does not need servicing, enters,a power conserving mode during a time period'265. The master then activates for a time period ;to monitor the next HELLO message from the bese.r If the master has data to send to the base, it..transmits the data during a time period 271. Likewise, if the base has data to send to the master, the base~~~
transmits the data during a time period 269.
Once the data is received yr sent by the master, it may again enter a power conserving mode.
While HELLO message protocol is discussed, a number of communication protocols may be used for communication between the base and the master device. As may be appreciated, the microLAN master device acts as a slave to base stations in the main communication network. .
Generallyr the communication exchange between the master and the slave is similar cc that described above in reference to Fig. 6b.
Block 273, however, illustrates a situation.
where the master encounters a communicatio.~.~.
conflict, i.e., it has data to send to or receive from the slave on the subnetwork at the same time it will monitor the main network t n HELLO messages from the base'. If t~e,master has two radio transceivers, the master can service both networks. If, however.~the master only has lone radio transceiver, the mister chooses to service one network based on network priority considerations. For example, in block 273, it may be desirable to service the slave because of the presence of data rather than monitor the main network for HELLO messages from the base. ~ .
On the other hand, in block 275, it may be more desirable to monitor the main network for HELLO
messages rather than transmit an idle sense message on the subnetwork.
Figs. 8 and 9 are block diagrams , illustrating additional power~saving features according to the present invention,~.wherein ranging and battery parameters are used to optimally select the appropriate data rate and '' power level for subsequent transmissions.
Specifically, even though network devices. such as the computer terminal 7 iW Figs. 1'2 have the capability of performing high power ' transmissions, because of battery power concerns, such devices are configured to utilize minimum transmission energy. Adjustments are made to the~data rate and power level based on ranging information and on battery parameters. Similarly, within the microZ,AN network, even though lower power transceivers are used, battery conservation issues also justify the use of such data rate and power adjustments. This process is described in more detail below in reference to Figs. 8 and 9.
More specifically, Fig. 8 is a block diagram which illustrates a protocol 301 used by a destination.microLAN
device and a corresponding protocol 303 used by a source -31- ..
. , microLAN device to adjust the data rate and r possibly the power level 'for future~..transmission between the two devices. yt a block 311. upon receiving a transmission from a source device.
the destination device identifies a range value at a block 31.3. In a low cost embodiment, the range value is identified by considering the . , received signal strength indications (RSS'I7 of the incoming transmission'. ~1'lthough. RSSI , ' ' 10 circuitry might be placed in all microLAN
radios, the added expense may require that only microLAN master. devices receive the circuitry.
This would mean that only'm~.croLAN master . devices would perform thefunction of the . .
' ~15 destination device. other ranging valuea~rmight . ;; . .
' also be calculated using.mo~e expensive...
techniques such as adding GPS (Global Position Service) circuitry to both.radios. ~In~such an.~
embodiment, the range valuetransmitted at.the 20 block 313 would consist of the GPS position of the' destination microLAN device. Finally.,. after identifying the range value at the block 313.
the destination device subsequently transmits the range value to the slave device from. which 25 the transmission was received.
Upon receipt of the range value from the .destina.tion device at a block 321, the source microLAN device evaluates 'its battery parameters' to identify a subsequent data rate for 30, transmission at a block 323.. If range value indicates that the destination microLAN device is very near, the source microLAN device selects a faster data rate. When the range value indicates a distant master, the source device 35 selects a slower rate. In this way, even without adjusting the power level, the total energy dissipated can be controlled to utilize only that necessary to carry out the 73164-128D , transmission. However, if constraints are placed on the maximum or minimum data races: the .~.
transmission power may also need to be modified.
Far example, to further minimize the complexity ,'~ associated with a fully random range of data ' ~ .
rate values, a standard range and set of several w data rates may be used. Under such a scenario.
' :' a transmission power adjustment might also need , ,~ to supplement the data rate~adjustment.
Similarly, any adjustment of power must take.
into consideration maximum and minimum operable levels. Data. rate adjustment may.supplemerit such limitations. Any attempted modification of the power and data rate might take into consideration any available battery pa=ameters ' such as those that might indicate a'normal or:
current battery capacity, the drain on the battery under normal conditions and during . . .
transmission, or the fact that the battery is~
currently being charged. The latter parameter proves to be very significant in that when the battery is being charged, the microLAN slave w device has access to a much greater power source for transmission, which may justify~the highest power transmission and possibly the slowest data rate under certain circumstances.
Finally, at a block 325. an indication of the identified data rate is transmitted back to the destination device so that future transmissions may take place at the newly selected rate. The indieation of data rate may be explicit in that a message is transmitted designating the specific rate. Alternately, the data rate may be transferred implicitly in that the new rate is chosen and used by the source, requiring the destination to adapt to the change. This might also be done using a predetermined header for synchronization.

Fig. ~ illustrates an.,~alternate'embodiment for carrying. out the data rate and~possibly~
power level. adjustment. At,a block 351 upon binding and possibly periodically, the source microLAN device sends an indication of its current battery parameters to the destination microLAN device. This indication may be each of the parameters or may be an averaged indication of all of the parameters together. At a block 355', upon receipt, the destination microLAN
device~355 Mores the~battery parameters for ~ .
indication) . Finally, at~ a~ Mock 358, upon receiving a transmission from the source device, ' based on range determinations and the stored.
battery parameters, the destinat.ion.terminal identifies the subsequent.d~ata rate land possibly power level). Thereafter, the new, data r rate and power level are eommunicated to the source device for either explicitly or 20implicitly for future transmissions.
Moreover, it will be apparent to one'.
' skilled in the art having read the foregoing that various modifications and variations Qf this communication system according to~the present invention are possible and is intended to include all those which are covered by the appended claims.

Claims (4)

1. An RF local area network comprising:
a first network device, the first network device transmitting using battery power;
a second network device:
means within the second network device for identifying a range value indicative of the distance between the first and second network devices;
the second network device responsive to the identifying means by transmitting the range value to the first network device; and the first network device, upon receipt of the range value, identifying an appropriate data rate for subsequent transmission to the second network device.

2. An RF local area network comprising:
a first network device, the first network device transmitting using battery power;
a second network device;
means within the second network device for identifying a range value indicative of the distance between the first and second network devices;
the second network device responsive to the identifying means by indicating to the first network device an appropriate rate for subsequent data transmission to the second network device.

3. An RF local area network comprising:

a first network device;
a battery power supply disposed for powering the first network device, the battery power supply having battery parameter information;
a second network device;
means within the second network device for identifying a range value indicative of the distance between the first and second network devices;
the second network device responsive to the identifying means by sending the range value to the first network device;
means within the first network device for identifying the battery parameter information; and the first network device, based on the received range value and battery parameter information, identifying an appropriate data rate and power level for subsequent transmission to the second network device.

4. An RF local area network comprising:
a first network device;
a battery power supply disposed for powering the first network device, the battery power supply having battery parameter information;
a second network device;
means within the second network device for identifying a range value indicative of the distance between the first and second network devices;

the first network device transmitting battery parameter information to the second network device; and the second network device, based on the range value and received battery parameter information, indicating to the first network device an appropriate rate and power level for subsequent data transmission.