CA2219075A1 - In-building personal pager and identifier - Google Patents

Abstract

In accordance with the present invention, a radio personal communications device is disclosed, which is capable to receiving modulated radio signals, and capable of transmitting modulated radio signals using modulated backscatter technology. This device can operate in an Interrogation Mode, in which a set of mandatory data is transmitted from the device; in a Location Mode, in which the approximate location of the device can be determined, and in a Messaging Mode, in which data can be transmitted to and received from the device. The device is capable of transmitting information, using modulated backscatter, at more than one data rate. The device contains a display to display some or all of the data transmitted to the device. Alternate embodiments of the invention allow the device to also support pushbuttons to allow data to be input to the device. Alternate embodiments support a variety of powering mechanisms for the device, including batteries, charge storage devices, solar cells, a coil or other energy transfer device, etc. A recharging station is also disclosed in the event the power supply of the device requires recharging.

Description

IN-BUILDING PER'iONAL PAGER AND IDEI~ ;K

Field of the Invention This invention relates to wireless comml~nic~tion systems an.d, more particularly, to an in-building or campus area wireless commllnic~ti- n system using S m<~ t~l bac~tter tr~hnology.

R-~lgt~ Apl ~ ~ ~ t;~n~
Related subject matb. r is ~ closed in the following applir~tion~ filed colll;wl~nlly hel~witll and ~signPcl to the same ~si n~e hereof: U.S. p;ltent applir~ti~ n~ "Shiel-ling Technology In ~ Y~ ~ R~f-L ~r~tt~ ~ System," Serial No.
; "Encryption for Mo~llll~ted T~ catter Systems," Serial No.
"QPSK ~Yllll~tP.d R~rL~ *Pr System," Serial No. ; "~c-dnl~t~ R,~L ~
T oc~tion System," Serial No. . ; "Antenna Array In An R~ID System," Serial No. ; "Sube~ . Frequency Division Multiplexing Of Mo~ t~
T~cL-sc~tter Signals," Serial No. ; "IQ Combiner Technn'ogy In ~Sodu R~rL~ tt~r System," Serial No. ; "In-Building ~lodlll~te~l R~eL~ tt~r System," Serial No. , referred to below as the "Shober-Protocol" ~Ipplir~tion;
"T~ ~n~ive ~ ~ te~ acLrec~ttçr E2~flectrr," Serial No. ; ~p~nger, R~ e, And Cargo Reconciliation System," Serial No. . Related subject matter is also ~ closell in the following appli~tir n~ i ne~l to the sa e ~eSign~e 20 hereof: U.S. patent application 08/504188, entitled "~ tt-~l R~rL-sc~ter Comml-nir?ti- n~ System Having An FYten-led Range"; U.S. Patent Applic~ )n Serial No 08/492,173, entitled "Dual Mode ~od~ te~ R --L ~C~i~r System,"; U.S.
Patent Application Serial No. 08/~492~174~ entitled "Fùll Duplex ~odlll~t~rl R~rL-~r?~ttPr System,"; and U.S. P~atent Application Serial No. 08/571,00~, entitlçd 25 "T;nh~nre~ Uplin_ ~ ~Ill~t~iB~L ~ h- System."

Back~round of the Il.v~:..ti~)..
Security access syst~,ms have been developed to support the ~lton~tir ntifi~tion of ~lsolmel, for example to authorize the entrance of an elnployee into a building. an this appli~tion, we use the term "employee" to mean the person to30 whom we wish to provide service. Other appli~tion~ of the invention fl; ~closed here exist in which the receiver of the service is not an "employee", but that tt,rm is convellient and we will use it.) E~amples of such systems include the provision of a tinctive employee idenfifi~tif~n badge, perhaps with the employee's picture printed on the badge, which is eY~mined by a guard to det~rmin~ if access to the b~ ing is authori7e~l A next logical step is for the employee to carry an identifirq-tion card which electronically ~q,~lthori~çs entrance to the builAin~ For mple "mqgnetir" key cards exist which are keyed with a particular m qg~etir ~ign~tll~G; and which, when held in close ~ ity to a m~rnl~tir reader, can S authori~e building ent~qnre. Another ex~ is a card with a ma~neti~ stripe on the back (such as a m2gnetir stripe used on the back of a credit card); the employee then "swipes" the card through a card ;reader to allth~n7~ building entrance. Still another eYq-mple of the same concept is a "Smart Card" in which the card is placed either into or on top of an electronic reader which can access data stored on the Smart Card, and 10 this data is the means to ?~lth~n7f, building entrance. Recent trends are emphq~i7ing the use of mq-gn~tic key cards, m~gnetic stripe cards, or Smart Cards in o;rder to . llow building entrances to be unstaffed, and tl-~.Gr(jl~ to reduce costs.
Radio Frequency Tde ~liriralis?n (RFID) systems IG~.Se~ll the next logical evolution in the technolo~;ies Ai~c~ls~d above. RE~D is used for i~lPn~ifirqtion 15 and/or t~cl~ing of equipment, in~ , or living things. RFID systems are radio communir~tion systems that communicate between a radio ~ LnSC~ Gl, c,alled an Interrogator, and a number of ine~ e devices called Tags. In RFID sys~ems, the IntGrrogator cnmmllnir~tes to the Tags using mo~ t~l radio signals, an~i the Tags ~Gspond with moA~ teA radio signals. In one RFID technique, the Inter~gator first 20 ~ lsllli~ a messa~ to the Tag (called the Downlink); then the Interrogator transmits a Continuous-Wave (CW~ radio signal to the Tag. The Tag mQ--lQt~s the CW
signal using moA-ll:~teA b~L ~r~ ;ilg where the ~n~nn~ is electrically ~wi~hed, by the modul~ting signal, from being an absorber of RF r~Ai~ti ~n to being a reflector of RF radi~tion This MnA~ tecl BackScatter, or MBS, allows commlmic~tirn~ from 25 the Tag back to the Interrogator (called the Uplink). RFlD is used today in the ~u~ industry to fa~ilit~te building access; for example, the use of an RFIlD Tag to I;c~lly a lfh-)ri7~ entrance to a b~lilding, and/or to record that an in,dividual passcd by a particular Ic~tion I'his operation is called the Interrogation Mode; it is a mode of operation in which the In~ug~lol tr~n~mit~ a signal to all Ta~ss in the 30 reading field, requesting those Tags to respond with data which identifiPs this Tag.
The Tag then transmits this information back to the I~ lu~tol using MBS.
RFID t~chnology l~lesents a con~ çr~ble i-l-pr~ve-llent over the other building access technologies ~ cu~se~ above. The other t~hnologies have limited range (typically a few inches or less) between the reading device and the card or 35 badge. This limited range ~equire s the employee to place the card or badge in close p~ imily to the reading device. RFID technology allows this range limil~ti(~n to be relaxed, at least to some clegree, and in some cases relaxed ~lto~ther. Some RFID

~erhnqlogiPs are inherently short r ange (i.e., effective range of a foot or two), while other RFID te~hnolc-gies support an Interrogation Mode range eY.~ee~1ing ten feet.
This latter range is capable of providing a truly "hands free" ope~ti~)n where the RPID Tag does not have to be removed and held close to the reading device in order S to be read.
Beyond the security applit~tion~ di~ ss~ above, employees within a building or campus en~ ,e.~t have other needs as well. (For the Ien~in~er of this osllre~ we use thle term "build,ing" or "in-building" to mean either within a b~ in~ or within a campus ~ lent whlich could include a blliklin~ ) For 10 c~u"ple, "T ~tion~ applic~tion~ also exist. It is be ~-el;ci~l to know the h)calrion of a s~cifin Tag within the building, especi~lly in high-security b~liklings P~o~y~
systems, using infrared tr~n~ , have been developed to allow the loc~ion of a"Tag" to be tracked; however theIe a~e no comm~rcial products, and infrared terhnology suffers from lack of range and no ability to pass through ob~:ts. For15 ~y~mple~ if the infraIed tr~nsmitter is placed inside a person's shirt pocket, the co"""~ iration~ path is bl~A For large, expxnsive items, such as a tr;lctar usedin long~ t~n~e trucking, it may Ix cost-effective to place a Global Po~i~i onin~System (GPS) receiver in the tractor; thus, the po~ition of the tractor can lx d~te~",ined. However, GPS receivers are expensive, not suitable for use by 20 individuals, and not de~ign~1 for in-building applinati~)n~ Th~.erole, there are today no cost-effective solut-ion~ to the loc~hion problem for inclividuals within a building or campus e.lvilo~
In v:lAition~ low spee,d Idata "~mmlmirqti-~n~" applirq-tion~ are also present. Let us assume that an employee l~Ce,;V~s a very ~ t phone call, but25 ~e employee is not in his/her of fice at the time the call is lece;~ed. About the only -q~le option today is for a S~ to take the call and attempt to find the employee. Let us further assume that an employee receives a very h,l~li~nt cl~~ ic mail mes~a~ Systems are in eYi~t~nce today that allow the el~ctronic mail system to illt~/~;onl-~-,ct with a "Paging" system, so that all or part of the 30 elech~onic mail me~q~ appears on the clisplay of the pager. Toclay, Paging ls the most commonly used ll-echallism to support low speed wi~eless data commllni~ti- n~ However, there are drawbacks to the use of Paging syst~ms.
Some Paging systems suffer from poor in-building wireless coverage. A~so, some Paging services involve paying usage charges to a service provider on a Fer-35 ~n~?~ctinn basis. Within a buildillg or campus e.lvil~n.~ nt, it is possible to deploy awireless data LAN; however these products are still relatively expen~ive. Thel~rc low-cost sol~ltion~ do not exist today for low speed wil~,lcss data commul~ir~tion~

within a building or campus environm~.nt Th~ ,r~re, we have seen that RFID technology, which is inh~l~,.,aly a low-cost t~,rhnology, is making inroads into secul;ly app1iration.e for the pu~03~ of identifying Tags as they pass a s~ cific reading device. However, there are no low-5 cost techniques to provide 1Ocz.~tiom inf~rm~ion within a building or campusenvir~nm~nt and there are no low-cost techniques to provide low speed wireless data comm1miratione information within a building or campus el1vilum~ent. There are also no systems that integrate the above capabilities -- Interrogation, I oczltinn, and Low Speed Wireless Data Co1mmnnir~tion~ (or ~eee~ing) -- in one !iyStem. In lO this invention, we di~lose the design of a low cost ~.~nal commnnicationc device uti1i7:ing mo~ 1z~te~l bz.~sc~tter. l[his device can be used to integrate the llmction~
of Security, T~1ion, and M~ss~ing in a single system wi~h a single h~rr~~ e.
This device thus can provide i"~ ved ,~;u,i~ as well as cost~rÇ~ive in-building or campus-area loc~tion and comm11niczation~ services.

15 Summary of the Invention In accordance with the present invention, a radio ~,~na comml1ni~tionC device is ~ osel1~ which is capable of receiving m~ln1z~t~d radiosignals, and capable of ~n.cmitting mod111zlt~.d radio signals using modulated ba- L ~c~ tec hno1- gy. This devi,ce can operate in an Int~llu~ tion Mode, in which 20 a set of m~nd~toty data is trz~n~mitt~.d from the device; in a T ~cz tion Mod~, in which the al)pfoAil,late 1Orz~ti~n of the device can be de~"nined, and in a ~sQ~rinF Mode, in which data can be tr~n.~mitted to and l~ceived from the device. The device iscapable of tr~nsmittin~r inf~rm~tion, using modn1~ted b~cL-.~att~.r, at more than one data rate. The device co~ a di.splay to display some or all of the data ~r~n~mitted 25 to the device. ~1t~rn~te emborlimf~nt~ of the invention allow the device to also support pushbuttons to allow data to be input to the device. ~1tP.rnst~ em~iments support a variety of pow~ling mech~ni~m~ for the device, inr1~ in~r b~tter~es, charge sto~age devices, solar cells, a coil or other energy ~ r device, etc. A rl chargring station is also ~ r1ose~l in the event the power supply of the device requir~ s 30 recharging.

Brief Des~. "~t~- n of the Drawin~r In the drawing, FIG. l shows a block ~ ~m of an illustrative Radio Frequency Td~,ntific~tirn (RFID) system;

FIG. 2 shows a block diagram of an illustrative Interrogator lJnit used in the R~ID system of FIG. 1;
FIG. 3 shows a block diagram of a Tag Unit used in the RFIl) system of 3;IG. 1;
FIG. 4 shows a block diagram of a Personal Pager and IDenti~fier (PPIlD);
FIG. S shows one embo~lim~nt of the physical layout of a PP[D;
FIG. 6 shows an ~lt~rn~te em~im~nt of the physical layout of a PPID;
FIG. 7 shows an RF ]Detector i~ ~d in a PPID;
FIG. 8 shows a Docking Station and how the PPID could be ori~onte~
with respect to the Docking Stahon.

D~ Description MBS Operation We now (1~srribe how a typical RFID system, ntili7in~ MBS, o~ tV S
15 With reference to FIG. 1, there is shown an overall block ~ m of a tr~
RFID system. An Appli~tions Processor 101 comm~nic~tes over a Loc~ Area Network (LAN, 102), which cou1d be wire~d or wil~lcss, to a plurality of Interrogators (103, 104). The Interrogators may then each co..llllunicate with one or more of the Tags (105, 107). For example, the Interrogator 103 I~CcivcS an 20 infQrm~tion signal, typically from an Applir~tion~ ~ Jcei.sor 101. The Interrogator 103 takes this inform~tion signal and P~oce ssor 200 ~o~.ly formats a Downlink me~gç (Inf~rm~tion Signal 200a) to be sent to the Tag. With joint lefe~c.~cc to FIGS. 1 and 2, Radio Signal Source 201 synthçsi7~s a radio signal, the Mo~ tor 202 m~ tçs this Inf rm~tion Signal 200a onto the radio signal, and the 25 T, .~ 203 sends this mcYl-ll~t~l signal via Antenna 204, illu~lla~ ly using ~mrlitl~e mod~ tiQn, to a Tag. The reason ~mplitl~de m~ ti~n is a Cl-mmon choice is that the Tag can demodulate such a signal with a single, ine~
nonlin~r device (such as a diode).
In the Tag 105 (see lF~G. 3), the Antenna 301 (rl~uel-lly a loop or patch 30 s~nt~nn~ ce;vcs the m~llll~t~l signal. This signal is demodlll~t~, directly to b~cb~ l, using the Detector/~o~1ul~tor 302, which, illu~LIa~ivcly, could be a single Schottky diode The result of the diode detector is essçnti~lly a demod~ tion of the inroming signal directly to baseband. The Inform~tion Signal 200a is thl n amplified, by Amplifier 303, and synchroni7~tion recovered in Clock Rec:overy 35 Circuit 304. The Clock Recovery Circuit 304 can he enh~n( e~l by having the Interrogator send the amplitude mo~ tP~ signal using Manchester encoding. The reslllting information is sent to a Processor 305. The Processor 305 is typically an inr x~ ive 4 or 8 bit microprocessor; the Clock Reco~ Circuits 3W can be imrl~.n~ fll in an ASIC (Application Specific Integrated Circuit~ which works S together with or is incol~ ~ted within the integrated circuit cou~ g Processor305. This Processor 305 can also serve as the driver for an optional Display Unit 309 should this Tag require a display. The Processor 305 generates an Inf~rrn~ti~n Signal 306 to be sent from the Tag 105 back to the In~..~ . (e.g., 103). This Tnform~tion Signal 306 is sent to a l~o~ or Control Circuit 307, which uses the 10 InFormation Signal 306 to mo ~ te a sn~ frequency gen~a~d by lthe Frequency Source 308. The Frequency Source 308 could be a crystal oscillator separate from the Processor 305, or a signal derived from the output of a crystal oscill~tor, or it could be a frequency source derived from signals present inside the Processor 305 -- such as a multirle of the filn~l~ment~l clock frequency oFthe 15 Processor. The~odnl:lt~l SUbCA.I;e. Signal311 isusedbyDetectorlMa~ t~r3o2 to modulate the m~illl~t~d signal received from Tag 105 to produce a m~ tlo~
b~c L ~c~t~- (i.c., reflected signal). This is ~ccom})li~lled by swi~l~ing on and off the Schott~y diode using the Mofl~ re~ Subc~rripr Signal 311, thereby ch~nlring the r~fl~t~nre of Antenna 301. A Battery 310 or other power supply providcs power to20 the cil~;uilly of Tag 105.
There are a variety oi.~ techniques for using ~ndlll~te~ R~cL-~c~tter (MBS) to send inform~tion from the Tag to the Interrogator. In some ME~S
technol~giPs, the M~lul~tor Circllit 307 of the Tag g_n~"at~is a ~noflul~tecl signal, which is amplitude m~nl~t~P~l by an InfQrn~ti~n Signal 306 at frequency f2. If the 25 Radio Signal Source 201 genela~e~s an unmof~ tp~l r~ucll~;y fl, then the Inte.l~ receives signals inside of the range (fl - f2) to (fl + f2), and ~n~rally filters out signals outside of that range. This could be termed the "MBS at ba~eb~n~
approach. Another approach would be for the Tag to ~,n~,.ate two dirre.~llt s~ - L~u~- -ric s. The inf~ rl~ ~tion could be con~ ,d in a Çl~uen; y-shift 30 keyed (FSK) fashion with the subcarrier frequency tr~n~iti~ning be~ these two~lc~luellcies. Other mof~ ti~n srhPmes are pos~iblp as well, such as Pha~se Shift Keying (PSK) of a single subc~rrip~r frequency (e.g., BPSK, QPSK) or other complex modlll~tiQn sçhprnp~s (e.g., MFSK, MASK, etc.~.
~Phlrning to FIG. 2, ~he Interrogator 103 lccei~,s the reflected and 35 m~lll~tPd signal with the Receive, Antenna 206, amplifies the signal with a Low Noise Amplifier 207, and ~1emodl~1~tes the signal using homodyne detecd~n in a Quadrature Mixer 208. (In some Interrogator de~ign~, a single Transmit (204) and Receive (206) Antenna is used. In this event, an electronic method of cq-n~elin~ the tr~n~mitted signal from that received by the l~,cei~ chain is nçed~; this could be ~comrlicll~ by a device such as a Circulator.) Using the same Radio S ignal Source 201 as used in the transmit chain means the demo~ q-tion to bq~eb~n~ is S done using Homodyne ~3etection; tnis has advantages in that it greatly red!,uces phase noise in the receiver circuits. The Mixer 208 then sends the Demor~ te~ Signal 209 (if a Quadrature Mixer, it would :;end both I (in phase) and Q (quadrature) signals) to the Filter/~mrlifi~:r 210. The res~ltin~ filtered signal -- which in this invention is an Tnf~Tm~tinn Signal 211 carried Oll a subc~ . ;er -- is then ~lemn~ t~A from the 10 su~c-q-rner in the Subcarrier Demodulator 212, which then sends the Tnf~Tmq~ion Signal 213 to a Processor 200 to determine the content of the messq,~, 1'he I and Q
channels of Signal 209 can be combined in the Filter/Amplifier 210, or in the S~bcq-rr~er Demodulator 212, or they could be combined in the ~ucess~ 200.
Using, e.g., the above technillues, a short-r. nge, bi-direction ~l digital 15 radio commllnir~tion~ ch~nnel is implem~nte~ A relatively in~Y~n~ive imp'.~ on is achieved using, as exemplary c~"llpoll~nl~, a Schottky diode, an ~mrlifier to boost the signal strength, bit and frame Y,y,lcl~ i7~tion circuits, an in~Yrn~ive 4 or 8 bit microprocessor, subc~,;~r gen~Lion circuits, and a battery.
Most of these items are already ~-~ n-- r~cl~ - . ed in qll~ntiti~s of milli- n~ for other 20 applic~tinn~7 and thus are not overly expensive. The circuits mentione~ ~Ibove for bit and frame synchroni7~tion and fc~r subc~. . ;P r gelle.a~ion can be implemented in custom logic ~,ul-~unding the microprocessor core; thus, except for a relatively small ~mollnt of chip real estate, these pllnf~tiQn~ come almost "for free."

Na.... ................................ ....,.~! ,rs~ Operation Using the above 1,71~'edUIeS, a two-way digital radio commllni~tion~
ch~-n~?l can be constructed. We desire to extend the range of this tWo-W;ly digital radio comm-lni~tiQn~ channel as much as pos~ible. This involves both ~ Ytf-n~ling the range of ~e Down]Link and a]Lso eY-t~n~ling the range of the Uplink.
FYten~ling the range of the Down]Link involves severa]L factors. The 30 Downlink is generally an amplitude mo~ tçd signal, which is easily anld in*~ cly detected by a single nonlin.o~r device, such as a micl~w~, diode. It isimportant to match the im~nces belwccn the ~ntenn~ and the diode to avoid ~Luilous signal ~tten-l~tion The data rate of the Downlink must be limited in order to reduce the noise bandwidth of the Downlink signal. We now discuss how the Tag35 can filter out unwanted signa]Ls without increased cost. The Antenna (30]L) not only ~.rc.~-ns the tasks of receiving tble ~F signal, but it a]Lso filters ~F signa]Ls outside of ' CA 02219075 1997-10-27 the q~ 9 bandwidth. For example, at 2.45 GHz, allowable RF carAer L~i~el-eies are from 2.400 - 2.485 GHz. The design of the sntçnns frequently a patch qntçnns"
covers this frequency band but filters out fre~nçnriçs beyond this range. An ideal fIequency response would be for the snt~nna, sensitivity to be within 3 dE~ across the S allowable frequency range, but to fall off rapidly beyond this range. In q~1Aition, the Amplifier (303) also acts as a filt~ r in the sense that the ~mrlifi~r is ~le~igrnç~1 to only pass ~mplitude ~1-1lsted (AM) signals that are within a certain ~as~b~ld around the ~x~t~ Downlink data rate, which is typicalliy a few Icilobits per sec~nd.
Therefore, q.1thongh the Tag is relatively simple, it has filtçringr cq-rqbi1ity to filter out 10 both ~F signals whose frequency is outside the Antenna bandwidth, and ;llso to filter out AM signals whose frequency is outside of the ~mplifi~r pq~sbqn-l This Tag desigrn is also not greatly sensitive to RF trqn~mi~sion~, inside the band o~ the ~qllt~n~-A, whose modniAtion scheme is primarily co~ t envelope. Thus, thiis design allows a robust Tag which is ~ to many potential hl-e.r~.i,lg sigrna~ s.
FYt~n-ling the range l~f the Uplink also involves several factors. First, the noise bandwidth of the UplinL signal must be reduced _s much _s pos~ihl~. A
numher of useful applinq-tion~ can be implf ~~-el-~l even if the data rate of the Uplink sig~nal is limited to a few bits per second. Indeed, this limit~tion of the data rate can be taken to the extreme in which Ihere is no data mod~ tçd onto the sing ~e 20 SnbCArr;ÇrfreqiUenCY; in this case, the mere presence or absence of a sign~ cei~
at this subcall;e. frequency in~lir7ltes an "acknowle~gmPnt" or "no acknow~ mçnt"
to a previously received mess~ge We further note that the snb~ frequency can be relatively accurately clet~rmin~ For çxAmple, commP,rcially available crystals exist with a frequency of 32kHz"md an accuracy of i 100 ppm. Thus, the fr~quency25 of this crystal is known to i 3.2 H[z. The Tag thus gen.,.aL~s a snbc~ r ~requency, f 5, of great accuracy. The Interrogator l~cei~ es the refl.octed signal, and dçmodlllAtes it as di~cll~ above using Homodyne detection. The Filter ~mplifier (210) and S~lbc~ r l~ernocllllAtor (213) function could theri be implçm~ontYl toget'lh~r, inside a ~l~ cessof such as a DSP. Naulowl,alld filt~ring Al~orithm~ exist in the 1iL~.~Lul~
30 which can ~.Çullll digital filtering of the signal with a bandwidth of less Iharl 10 H[z, and where the first sidelobes are ~ep~ ,sed 60 dB. Then, the signal strenc;th of the signal received through this digital filter is measured, and that strength is coln~ d to a l~r~ .lce signal strength whi<,h is sllfficiçntly above the average nois~ in that channel when no signal is present such that spllrioll~ noise spikes a~e not 35 mi~inle.l"~d as actual signals. l:n this manner, very weak Uplink signals can be reliably detecte~l It has been found that, using these techniques, roughly equivalent range in the Downlink and the Uplink car~ be achieved.

We now discuss the loc~tio~ of the subcarrier frequency f5. MBS
systems exhibit noise in the Uplink signals due to reflectione of the RF saurce from any number of reflectors. WaLlls and metaLl objeçts reflect RF r~ qtion; these reflf~t~l signals are received by tlhe Interrogator 103 at the same carrier r~ n~;~ as S they were tr~ne-mittç~ The Qua~rature Mixer 208 is o~.~d as a Homodyne Detector and thus is used to caLnce:l these reflf ~ti~ ne However, other refl~ ctors generate reflected noise at frequencies away from the main carrier frequellcy - either from Doppler shifts or, more likeLy, from reflP~tione off of electronic eqllipmPnt o~tillg at freq~lf~n~;f~ s near the '3~ . ;f ~ Frequency. One paLrticularly ~1;ffi-~ll1t 10 source of noise is fluorescent lights, which have been shown to produce noise not only at their fimd~mental 60 Hz ~iin the United States) frequency, but alsa at ovcl~ne L~uencies well up into the tens of tholle~n~le of Hertz. It has been founcl especi~lly helpful to locate the subca~ ,r frequency fs such that it falls b~,l~n mllltiples of the fimd~ment~l 60 Hz frequency. From the 32 kHz crystal, simple circuits can 15 g~;ll.,.~t~ the app~ liate subc~-;~. frequency.

Multiple Mode Operation The basic fG~ul~s of multiple mocle opP~ti- n are that a) the Tag must be capable of receiving a Downlink mess~; b) the Tag must be told what type of Uplink m~:ee~ it is to transmit, whether it be an actual data mesea~ (hi~her bit rate 20 mode) or a simple acknowledgment mcee~ (long range mode), based upon infnrmzltion received in the Dow~llink meseag~; c) the Tag ~L~Iin~i~ the ~ cs~d type of Uplink m~ee~g~. and d) the Interrogator in~~ ,t~ the Uplink m~s~e~ge received in a proper manner. Several diffe~nt types of acknowle~grn~-nt meseagesin the long range mode can exist. Generally, an acknow1etlgmenf mf ssa~,e has a d~ata 25 rate which is much less than the dLata rate of a~n actual data mssea~r~ (the higher bit rate mode), thus allowing filterinlr over a much smaller f~u~ y band, a,nd thus allLowing greater range than the higher bit rate mode since the noise band~idth of the e d signal is lessened due to the narrowband filLtering. Thus, a~n acknowledgment mçss~ge could consist of a low bit rate data m~ose~ge~ or it could 30 consist of a single bit of information. As discussed above, to send a singlie bit of inform~fion, the Tag could generate an unmo~lnl~te~ s~lbc~ . ;e- freqLuenc~r which could be mo~ tecl onto the in~is~ent signal, using mo~ t~ ba- L ~ ' The Interrogator would then receive a reflect~l signal with a single frequency tone.Narrowband fi~Ltering techniques c ould then be used to reduce the noise b~ndwidth 35 and d~,t~ nillc the presence or absence of this signal.

.
The Tag 105 detects and assembles the bits of information ~nt from the Inte~ogator 103 into a complete Downlink m~s~z~ge. Typically, a pattern of synchroni7~tion bits is ~ at the beginning of the Downlink mPssz ~e; thesebits allow the Tag to acquire bit and meS~gp~ ~yllcl~ i7~;on; enabling the Tag to 5 ~.lnine the be~rinning and the e:nd of the Downlink messzlp,.o. The I~ownlink meSS~ cont~nte would include an Address, a Comm~ncl, opt~on~lly include Data, and also include Error Detect. The C'.omm~ nA or Data portion of the Downlink mçScq~ could inclic~te that the Tag 105 should return a Message to the Interrogator, ~or eyztmpt~ the Tag could return stored data, such a~c the Tag ID, or other 10 application-specific Aata. Another type of Downlink me~cqge could inAir:~te ~hat the Tag should send back only a single-bit acknowledgment m~ss~ge Thus, the Processor 305 of the Tag 105 d~ r,s, in ~G~ns~ to inf~ rmz~tion in the Downlink mçss~, what type of Uplink signal to tran!;mi~: a data mf~cc:~g"~ or a simple acknowlPA~n~nt mesc~ There are several ways that tlhe Tag15 105 may transmit either a data mf s~a~ or a simple acknowle~l~rm~nt mPssa~ so that the Interrogator 103 can, relatively easily, receive and distinguish between these two a;rr~.~.,. types of mecs~gf~s I~f~mn~ to FIG. 3, in the event t~hat the Tag 105 is to send a multi-bit information sigrnal, Processor 305 sends the Inf~nt~tion signal to the ~n~ t~r Control 307, which mod~ tes the signal from Sllbc~rn~r l~requency 20 Source 308.
In Tag 105, Processa,r 305 sends the Tnf~rm~tion Signal over the Information Signal Lead 306 shown in FIG. 3. In the event that Processor 305 of Tag 105 is to send a "single tone'~ mPss~go con~i~ting of a single information bit, the Information Signal Lead 306 is ml~int~inçd at a first logic state to in~ tf that no 25 infor n~ti~n mçssa~f is to be sent. Thus, an unmodul~ted subca,l;cr frequencysignal is uU~ r~ d by ~~ tf~r Control 307. In the event that ~ocessolr 305 ~ t~ ~ s that a multi-bit mçs~gte is to be sent, the Infornnation Signal ]_ead 306 co~ , the multi-bit mçss~ to Mcdl~l~tor Control 307. This multi-bit mf ~s~ge r<~ ion signal) is then used to mofilll~te the subr~ ,r frequency using one of 30 several possible modul~tiQn techniques, such as annplitude, phase, frequency, or code modnl~tion.
The Interrogator 103 (FIG. 2) ~ modlll~tl~s the subc5~ ~ ;C~ si~nal from the received RF signal, and then applies filtering. Given the spe~ifirs of the subcarrier frequency, a suitable filt~ring amplifier is utili7~ Subc~. . ;f.r 3~ Demo~ tor 212 then demod~ tes the subcs . . ;er signal. The Processor 200 then .r~""s the digital signal proces~ing n~ess~ry to decode the informatian. In someimpl~mentAtion~ of this invention, the I!rocessor may be a Digital Signal Processor . CA 02219075 1997-10-27 (DSP); in others, a convention~l Microprocessor could be used. To reco~er a "single tone" acknowledge signal from Tag 105, cQnci~ttng of a single subc~tTier tone, the filtP.rin~ ~mplifiPr would be a na~ wband filter. While col~e ~I;on~l filter t.orhnntngies could be used, it may be most effective to utilize the DSP m~ntinnf-A
S above as a n~uluwl,~ld filter. The: subc~ frequency of this single tone: is well known; as the Tag 105 would typically use an in~Ypen~ive crystal as the irequency source. Even with the limited ac~ a~y of that crystal, the subca l;~ frequency could be known to an ac.~ r of a few Hertz. Thus, very n~uwl,~d filr,ers could be used. Since the acknowledge signal ~ ~nse from Tag 105 is used to extend the 10 range of the RFID system and consequently would likely be a very faint s,ignal, it places an ~ldition~l burden on the nallù~l,~ld filter of filtering ~mplifier 210.
Another way that the DSP mPntic)nP~l above could be used is to dyn~mic?~lly search for the frequency co-llponellts of the UplinL- signal. l'his could be ~rcomrlished by ~-rol,.~ g a Fourier Tli~n~r~- ... on the incoming data stream, 15 perhaps using a DSP, or using ~rocessor 200 of FIG. 2. In this manner, tl~e rnllltip'o signals ~ senl;ng a mofl~ te~ subcarrier signal could be dirÇ~ ltiated; or, a single subc~rier signal of uncertain data rate could be l~co~ d by usingr the Fourier Transform to search for multiple signals.
Thus, we have shown how a mo~ tecl b~c~s f t~ ~ commun ir~tiion 20 system can operate in two modes - one in which the b~r~ttered signal is mod~ tel1 to provide a high data rate Uplin_ commnnir~tinn ch~nnel~ an~l one in which the b~-~L *c~f Ir ~,d ch~nnrl is modlll~teA with a low data rate signal, ~ ~ ps a single tone, to provide an Uplink acknowledgment signal that can be det~ct~d at great di~t~nce~-We now use and exte:nd the above di~cu~sion so that several Modes of operation are present, where the aLrr~ ,nl Modes are char~teri7~1 by dir~e~l~l uplink data rates. The first Mode to be ~ c-ls~ed here is the "Interrogatian Mode."
The Interrogation Mode begins with the Interrogator lli n~ g an I~ lug~fion Signal to the Tag. The Tag receives this Interrogation Signal, ~ecocles it, and 30 d~,t~ ines what actions to take based upon the deco~3ed Interrogation Signal. In a "standard" Interrogation, the Tag would be requested to transmit a particlllar set of data (called here the ~nri~t~ry Data) back to the Interrogator, using the MBS
technique discussed above. E ach Tag in the reading field of the Interrogal or that Ieceives dle "standard" Interrogation responds with its ~n~i~tory Data, llsing a35 protocol ~ sed below. The Interrogator also tr~nemit~ as part of the ''standard"
Interrogation Signal, data int~nded for each and all Tags. F.Y~mpl~s of sLIch data include time of day, framing and other synchroni7~tion information, etc.

CA 022l9075 l997-l0-27 Beyond the "standardl" Interrogation, other types of InterrogqtiQn~ are possible as well. For example, the Interrogator, after identifying a specific Tag using the InteTrogation Mode, could ila Is,~ qd~litionql data to that Tag to be stored in the Tag's memory. The Int~lo~lol could also request the Tag ~ lil other data, S stored in the Tag's memory, back to the Interrogator. These D.tlAitionql data commllni~qtion~ could be ~- r... 1.l~ at the same data rate used in the "st~ nd2~d"
Interrogation. Thus, the InterrogaLtion Mode is used to~ mil comm~n-l~ and data to each and every Tag, identify a specifiic Tag in the reading field, and als~ used to communicate in a bi direction~l manner with that specific Tag. In the Int~rrogation 10 Mode, the data rate required in the, Downlink is typically not large, since ~the In~,.og~lion Signal only must contain enough bits to request all Tags in I he reading field to respond. Even when si~nifi~nt amounts of Downlink data are ~ ~.~...;l~3, in many appli~tion~ this process does not take place frequently and the Downlinkdata rate is not criitical. In the Uplink, the data rate is typically much largl~r tlian the 15 Downlink data rate, as the ~nd~tory Data must rl~uel-lly be tran~mitted in the Uplink in a time critical manner. Therefore, in the Interrogation Mode, ~ ~e have an asymmetry in required data rates in the sense that the Downliink data rate is smaller than the Uplink data rate.
For the second, or T~ tinn Modc, the I~ ogator transmits an 20 Interrogatiion Signal to the Tag cont~ining the address of a specific Tag ta which this Interrogation Request is directe~ In this Mode, the Tag is not ~~u~a~l I o respond with the ~nd~tory Data ~ euss~ above. Tn~tefld, at least in some embodiment~, the requested response is a simple: acknowledgment. One embodh~ t of a simple a~knowledgment is a conct~nt-tone signal. Using the nalluwl,and te~hniq es 25 ~ c~ e~ above, a conct~nt-tone signal can be l~ce;vcd by the Interrogator at a range far beyond the range of the Interrl~gation Mode. Therefore, in the T~hnn Mode, we have an asymmetric commllni~tionc path which has greater data rate in the Downlinlc than in the Uplink.
We now discuss metho~c to dett~rmine the lot ~tinn of a specific Tag 30 (105). Let us assume that the system cu~ ly has no inforn~tit n as to t]le lnc~tit)n of this Tag. Then, an Interrogatic~n Signal is ~ fl by all Inlellu~,a~ols, and all Interrogators listen for a response. In one embo~1imt nt, each Interrogator can dete....i~-e the signal strength of the l~ceivcd signal (if any), and those si~nal strengths can be reported to a central control element. The d~ t~,,.... i n~l ;on of lc~hon, 35 based upon this data, can be done in several ways. The most obvious way is for the control element to det~nnine which In~.logalo~ received the strongest si'gnal strength. Then, the location of the Tag is equal to the loc~tion of that Int~ rrogator, to an accuracy of the effective range of that Interrogator. A mone complex method could be implemented if more tha~n one Interrogator received a retu~ signal. Then, given a knowledge of tlhe spatial position of each Interrogator, a refinPme~t on tlhe above positic)ning could be aclhieved. For eY~rnrle, if two Interrogators nxeived a S return signal, of equal signal strengths, then the Tag's ~ inn could be estim~ted at half way ~L~eli those two Intenrog~tion~ If three ~nterrogators receive~l a return signal, then a "triangulation" could be ~.Ç .~lueA It should be ~ nl that these methofl~ will ~,- f~ . .-- better if there are line-of-sight paths Ix l~n the In,terrogators and the Tag; if t~he RF commllni~:ltion~ pat~hs rely on reflf~ctir)n~, distortedl lc~ti-~n 10 results could be obtained. However, it is likely that l~tion~ can be de~. ,nilled to an accuracy of the err~clive range of an Interrogator. Based upon which I~ gator receives the simple ackno~,vl~A m~nt, a T oC~tion capability can be imp~rn~n~A
For the third, or Mçss~ging Mode, the Interrogation Signal not only com~in~ the address of a Tag or Tags, but it also may contain data intend~,d for that 15 Tag or Tags. The Tag or Tags whose address m~tnh~s the Tag address in the Interrogation Signal could be requested to store that data in the Tag's memory, or ~r~..,.. some other function with that data. There are several possible responses to an Interrogation Signal for the ~ess~ing Mode. If the cr~mm~nA within thc Interrogation Signal ~~ue~ the Tag to simply store data, then an ackno~ledgmçnt 20 to jndic~te s~1cces~ful receipt of the meSs~gç could be a few bits or even a single bit of inf~ rm~tion A single bit of ini'orrnation could be illlple.llent~d as a constant tone acknowled m~nt, as mer~tionçA above. Alt~,.n&lively, if the comm~nA wi~hin the Interrogation Signal requests the Tag to make a decision, or to transmit other data back to the Interrogator, then the response would be a meccqge cQnCicting of more 25 than a few bits of infcrm~tiQn. Th~ ;rol~, in the Mecc~ing Mode, we again have an a~y,-"llctric communi~tis~nc path which has greater data rate in the Downlink than in the Uplink.
We observe that the data-rate a .y~l"~lctry found in the T ~?~tioJ and l~ss~in~ Modes is similar to the: data-rate asymmetry found in a two-w;ly paging30 system. Paging tr~n~ . (comparable to the Interrogators Aiccllcse~l here) have much greater transmit power than is available in a two-way paging device worn byan individual (the paging device is comparable to the Tags ~licruc~rl here).
Therefore, data rates in two-way paging systems are frequently asymmeh~i~, with greater Do vnlink data rate than Uplink data rate. The T oc~tis~n and Messaging 35 Modes of the in-building MBS system ~licclosed here are similar to a two-way paging system, both in technir~l characteristics and in applil ~tii~-nc that ar~supportable.

CA 022l9075 l997-l0-27 It is also possible for a transaction that began in one of the above Modes to h~n~ition into another Mode of operation. The following is an illustral ion of the capabilities of the system. Let us assume we wish to commllnir~te with a Tag. A
~s~in~ Mode Interrogation Sngnal is tr~ncnlitt~l from the Interrogator to the Tag, S sçn~ling data to the Tag, and l~u~Ling the Tag to respond with a simple acknowleAgm~nt, which is l~_cei~_d by the Interrogator. Let us furtlher assume that, based upon the simple acknowle~ilgrnent ~ceil,ed by the Interrogator, the Interrogator wishes to request that additional data, ~Ih~s stored in the Tag's memory, be trAn~ A back to the Interrogator. ~ one embo~lim~nt the Interrogator ~ in~o.s 10 the signal strength of the simple ~Icknowlçdgm~nt signal. If the signal st~ength is 'oelow a certain threshold, then the Uplink data rate is limited to that data rate m)rm~lly used in the Uplink for tlle ~l~ssagin~r Mode. If the signal strength is above a certain threshold, then the radio comm~lnir~tiQnc path ~l~n the In~. Iogator and this Tag can support comm~ln;~P~ionc at the data rate n~n~lly used in the Uplink for 15 the Interrogation Mode. If the signal strength is below the threshold, then ei~er data communi~tionC can conlillue, but using the (lower) Uplink data rate of tl~e ~s~aging Mode, or a mes~gin~ could be L~ d to the Tag requesting that the Tag be brought into close ~ç~ ily ~o an Interrogator. How that request is received by a human being is described in the above-cited Shober-Protocol appli~ tion If the 20 signal strength is above the threshold, then data comm~lnic~ti~nc can con~in~le; but using the Interrogation Mode, as ~iccucced above. It should be obvious that, while the above eY~m~ shows how the Uplink coll~ tionc could take plsLce at either one of two possihle Uplink data rates, it would he possible to extend ~e ahove conce~l to support more than two Uplink data rates We now discuss how~ the three Modes of operation ~1iccucse~ above can coexist in the same system and he operational at the same time. We begin with the re~li7~tion that these Modes of operation, based upon the required data r~Ltes, support d~r~ t ranges from the Interrogator to the Tag. For eY~mr)le, the Interrogation Modle involves cignific~nt data ~lncmiccion over (relatively) short time periods, 30 such as when an individual waLlc$ by an Interrogàtor. The ~ ,d data ~ate is further increased, since there can be several individuals in the reading Iield at one time. Thus, a protocol (such as Aloha or Slotted Aloha~ is required to allow those m~lltirl~. Tags to respond with their Int~,r~galion data without m~ ly i,lt.,.r."ing, thus incleasing required data rate. Examples of data rate for co~ n~l;on from 35 the Tag to the Interrogator for the Interrogation Mode range from 50 kbps - 300 kbps. We also note that, in the absence of other factors, range and data rate Irade off against each other.

CA 022l9075 l997-l0-27 In summ~ry, we have two dirr~ ,nl '~asymmetries~ in data rates; greater Uplink than Downlink data rate for the Interrogation Mode, and greater I)ownlinkthan Uplink data rate for the TJoc:lti~n and ~Cc~ging Modes. Thus, the ,~rr~~
range for the Interrogation Mode is smaller than that of the T ~cation or ~Ps~aging S Modes, ~c~ the Uplink data rate l~ui~.llent is greater in the In~.~ ion Mode. In the "N~l~wballd Operation" section above, we Aicr1r,ce how t~ achieve cjgnjfir~nt range e~t~nCiQn. In that ~lic-cuce;on~ a Downlink data rate of a few kilobits per second, and an Uplink data ra~te of a few bits per second, give roughl~r co l-p~able range. This c~p?~bility co~lc~lu~ c- to the ~ .,...ents of the T~ti-~n 10 and lUess~ging Modes ~liccllc-ved above. For the IntelTogation Mode, a Downlink data rate of a few kilobits per second is also adequate. since relatively few bits of data in the Downlink are requirecl, and Uplink data rates are from 50 kbpis - 300 kbps. The Downlink range is the same for all three Modes. The Uplink ~nge for the T~c~tion and ~Içss~ing Modles is roughly the same as the Downlink range. The15 Uplink range for the Interrogation Mode is much smaller.
Here, we disclose how all three of these modes of oper~tion~
Int~.lu~ ion, T ûc~tis~n~ and l~e~ gin~, can be impl~omçnte~ in and supp~rted by a single, useful, inexpensive end-user device. We call this device a Person,al Pager IDentifier (PPID). A block diagram of the PPID is shown in FIG. 4.

20 PPID Description The Antenna (401) can be a patch or a loop ~n~enn~ The pat~:h ~n~
has certain advantages for a PPID. The patch ~nt~nn~ can be plated onto the substrate of the PPID device, and the back of the s~lbstr~te can be a "ground plane"
for the patch antenna. This general design will create a ~n~çnn~ "pattern" that is 25 pl~fe.~,nlially directed "outwards" - i.e., in directions away from the ground plane.
ReC~ ~ of the relatively small si:ze of the PPID - similar in size to an employee badge - and for radio frequency prop~E~tion reasons - it is common for RF signals at mic~wavc frequencies to be usecl. These rç~ue~cies, such as 2450 MHz - support very small patch ~ntf~nn~ designs (roughly 0.5 inch square).
Th~,.efc.G, a PPID device, worn as an employee badge, with the patch ~nle~ facing oulw~ds, will optimize radio commlmir~tion~ in front of the employee. In this way, when the employee moves low~ds a doorway with an Interrogator, the Interrogator can establish radio contact with the PPID as soon as possible. As discussed above, the Antenna (401) and Detector ~ tr~r (402) 35 designs are i~ t. The Amplifier (403) design is also illl~l ~nt. For the PPID
to provide the required Downlink range for the T ~ on and Messaging Mod~s, the -~mrlifi~r (403) must be able to bDost a very weak democ~ t~ AM signal to CMOS levels, operate over a very great dynamic range (because the PPII:I could be either very close to or very far away from an Interrogator), and draw very little current. Integrated over time, the ~mplifier (403) should draw at most a ~.ew S mi.;l~,a"l~s of current.
The ~cesso~ ~404) c an be a conventir n~l 4 or 8 bit microprDcessor as discussed above. The ~ocessol (404) must have a "sleep" mode, in which the current con~lmption is less than a microamp, and also have an "active" current eo. ~ lion of far under a milli~mp The role of the ~-~ce ssor (404) is to be the10 "brain" of the PPID, (l-~oflin~ the Downlink Signals, ~etermining what type of Uplink response is required, etc. The Processor (4a4) could be ~ d fi om a separat~ Crystal (430), or from aLm osci11~r cont~ine~l within the Processl~r (404).
Data Storage (420) i$ also present in the PPID. In one embodiment, the Data Storage (420) could be located in the microprocessor, as either volalile (Dr non-15 volatile storage. In an another emb<~liment~ the Data Storage (420) could. be locatedin another integrated circuit~ such as a EEPROM. The amount of storage ~u~ ,d in a PPID could range from as linle as a few bytes of storage up to tens o~F tho~ n-l~
of bytes of storage.
The Subcal~ tor (405) fun~tion~ as ~i~closed in the above-20 cited Shober-Protocol appli~tion, which is hereby inc~ td by reference. It iscapable of m~l~ ting an inf~rm~tion signal, of varying data rates, onto a S~bc~ . ;el signaLl which is generated by a Subc~ul;el Source (406). The S~ rrirr Source (406) could be an inf~.Yp~.~ crystal, c~r it could be a frequency source derived from thc main Crystal (430) used to clock the Processor (404).
To display information ~n~ d to dhe PPID using thle Inll,,.lu~ion Mode or the ~ sgin~ Mode, dhe PPID has a Display (408). To allow d e person callyLlg the PPID to respond to mrss~g~s~ Pushbuttons (407) are also present. A
P~ID could have one or more than one Pushbuttons (407).
We now obs~l ~e dhe ~imil~riti~s belw~n dhe PPID device as shown in 30 FIG. 4 and other devices on dhe market today. First, con-;~le- an ine~nsive "four-function" c~lr~ tor. Such a calculator con~i~t~ of a power supply, which could be eidher a battery or a solar cell; a plrocessor, typically a 4 or 8 bit microprocessor (or ASIC with a mic,ul,lucessor core); a display, which is typically a glass or plastic liquid crystal display; and pushbuttons to allow nl~merir~l inputs and functions to be 35 entered. We note that such a follr-function calculator is sllffiri~ontly h~ ~l sive today that in many cases these devices are given away as presents, souvenil~, etc.

Next, conci~ler an ine;~c~nsive quartz watch. The watch also has a battery, a processor (again, commonly a 4 or 8 bit micr~.ucessor or an ~SIC with a microprocessor core), a display, aLnd pushbuttons to allow the correct dat~ and time to be set. Again, such devices are commonly priced below $10 and are sometimeS
5 given away.
In summary, we see ~hat ine~n;,ive devices such as a c~lc~ tor or a quartz wrist watch already possess many of the elementC of a PPID as shown in ~IG.
4. The ~1riiti~n~1 components, shown in FIG. 4, are relatively ineYrencive; the Antenna (401) is plated onto a substrate and ~h~ r.~l~, only costs subs~te area, the 10 Detector ~od~ tor (402) is a single diode that in volume can be pu~-hased for under $0.10, the Amplifier (403) can be realized at a cost of under $0.50, the Subca l;er ~vrn~ tc~r (405) can be implt~mrTltç~ in a few gates costing a few cents, ~md the Subc~liel Source (406) can be an hle~l)ellsive crystal costing as little as '~0.15 (depending on the frequency of the crystal). Thus, for a total ~d~lition~l cost of as 15 little as $0.75, a calculator or a quartz watch could have about the same filn~1;nn~lity as a PPID.
We now con~ider the simil~rihes bel~,el~ a Pager and a PPID. l[he pager already has an ~ntenn~ (~ltho~lph likely tuned to the wrong frequency), battery, processor, display, and pushbuttons. However, Pagers are more e~nsi~,~, than 20 PPIDs because their radio cilr~ui~ , to obtain the range required of a Pagi ng system, is ex~ncive. A two-way Pager -- i.e., a device capable of not only ~ceivi--g a page but also tr~ncmitting a response -- will be even more exrencive.
Thc,,~,ro~,." the invention ~3isclose~ here is not based on taking relatively expencive t~rhnology -- like cont~in~A within a Pager -- and making it less 25 eypencive. This invention is based on starting with in~ypencive terhn~ gry -- such as that present in a c~lr~ tnr or watch -- and adding other ine~ ;ve elempntc such ~at the fllnrtion~lity is vastly increased.
One item to mention is that the PPID may require a larger display than that nr~Qlly available on a c~ tor or a watch. However, this d~es nol ~limini~
30 the fact that great additional -filnction~lity could be added to what is essenti~lly a very low-cost device, by using m<xllllate~ b~L ~ d radio t~rhnology, PPID Physical Design An illustration of a possible PPID design is shown in F~G. 5. The PPID
has overall ~imen~ion~ similar to that of an employee iflentifir~tion badge. The35 thir~ness of the PPID depends on the m~mlf~rtllring techniques used, the type of power supply used, etc. A typical thickness with would likely be about 1/16 inch;

CA 022l9075 l997-l0-27 ~ -18-however the te~hno10gy of "thin e lectronics" is rapidly advancing.
The Display (501) could be at the top of the PPID. Display ('iOl) is shown with two lines of display; :~sllming each ]Line ~ sent~,d 10-20 chq~Lc~e~s, then the total amount of display would be 20-40 characters. This amount of display 5 should be sl~ffi~ient for most app~ q~tion~ The Employee Photo (502) could be placed below the display; under the photo would be an idea]L place for the Antenna (503), which is plated onto the substrate, to be lnrqt~A To the left of the employee Photo (502) could be the Compq-ny Logo (504). Below the Employee Photo (502) and the C~ .y Logo (504) could be the Employee Name (505). Belo~ the 10 Employee Name (505) could be F'ushbuttons (506). The CoiiL (507) coulcL be located beneath the Co-,.pa ly Logo (504).
In an alternate embodiment (FIG. 6), the Employee Photo (61~1) r.. l.h.~y Logo (602) are on top, the Employee Name (603) is below, wi~h the Display (604) below the Employee Name (603). The Pushbuttons (605) are at the 15 bottom. As above, the Antenna (606) could be located imme~iqtely behind the Employee Photo (601). Above, we discussed the similarity be~wc;ell a fol~r- fimction cq-lc~llqt~r and a PPID. It would be strai~ rolwa~d, and add relatively little cost, to add enough Pushbuttons (605) to the PPID so that it will function as a follr-filncti~n cqlr~ q-tor in q~ ion to fun~-tioning as a PPID.

20 Power ~ s~ent An hll~l~nLt design ~al~ullet~l for the PPID will be the batt~:ry lifetime of the PPID. There are several approaches to the pn~ble.-- of battery life. One &~ L is for the PPID to prr)vi~de for a repl~q-ceqh1e Battery (409). In this nnanner the PPID can have a useful lifçtinn~ not limited by battery con~i~erations. The 25 ~disa~lva-l~ge of having a replaceable Battery (409) is that the PPID may not be water reQ;Qtqnt; however watch mqnl1f~qcturers have developed technLiques to made water re~;~fqnt or wat~ Of watches even with replaceable b~l~e- ;es Another approach is for the PPID to have a Solar Cell (410) as a power source. This ~p~ach has the following limitqtion Since PPID operation in low light con~1itit~n~ is just as 30 innportant as in bright light cQn~ tion~ the Solar Cell (410) would have to be c~?mplem~nte~ by an Energy Stolage Device (411), which would add cost. The combination of a Solar Cell (410'l and an Energ~y Storage Device (411) could be more expensive than the cost of a replaceable battery.
Another approach is for an Energy Storage Device (411) to be combined 35 with a device to re-charge the Ene,rgy Storage Device (411); such a device is a Coil (412). Energy could be inductive:ly coupled and ~ r~,llGd to the Energ y Storage Device (411) through the Coil (412~ if the PPID were placed in close ~ nily to arc~har~ g device with a similar coil operating at a frequency to which the Coil (412) was sensitive.
Another approach, of course, is for a Battery (409) to be built into the S PPID at m~nllf~rt lre time and the entire device perm~n~ntly sealed. This has advantages since the concc~ "c about water damage are not present.
Despite the above ~ f~ rn~;ves to the l,lu~',cm of pr~viding energy to the PPID, and regardless of which ~1~rrnqtive is s~ t~d. the PPID must be ~si~l with energy conse. va~ion in mind. It is for that reason that cnncern was .li SC~ f~
10 above about the el~tncal current draw of the individual compol~ of the PPID. A
final point to mf~ntion is that the E'PID would be o~.aled in a fashion where the device is not fully fim~tioning at every m~ment of time. The ~ocessor (404) can have the ability to "go to sleep"; i.e., to enter a state where active l~l.ace~ ~ is not taking place and where the current drain of the processor is quite low. The Processor 15 (404) can also direct the Amplifier (403) to "go to sleep", or to enter a stal,e where ~ownlink signals cannot be processed and the current drain is also low. Finally, the Processor (404) could decide, if there is no data to be displayed; e.g. if th~ last mrss~ge received has been acknolwledged, the Processor can halt the ope~tir~n of the Display (408). Of course, the PP~D cannot remain asleep in-lrfinitely, as then it will 20 i~ail to receive rness~ges and other com,..unir~tion~.
There are at least two techniques that can be used to ~lf t~ e when the PPID should be asleep and when it should be awake. First, the Processor (404) could be plu~l-m~d to wake up at routine intervals (many micl~o~l~ss~h:, have a w~tch-log timer for such a ~ ose). This technique is used by Pagers to allow the~5 device to sleep most of the time. The critical element in this technique is the ion of the length of time the PPID sleeps. To (3e~e~ .~.ine this length of time, several factors must be con~ red First, the PPID must respond to ~teIrogation Mode requests as discussed above. Then, the PPID must be awake rl~ue.llly enough so that, when ~le PPID enters the reading field of an Interrogator 30 O~laling in the Interrogation Mocle, the PPID can detect the Interrogation Mode signals and p~ ly respond. FOIeY~mr1P7 given an Interrogation Mode range of 30 feet, and a walking speed of 3 feet per second, the PPID must be awake at the very least every 10 seconcls, and more likely every 1-3 seron~ to be assured tl~at the Interrogation Mode signals are nolt missed. Second, the PPID must have a~ large 35 enough raltio of "total time" divided by "awake time" in order to reduce the current drain enough so that the PPID can be powered by a reasonably small battery, such as a coin cell. This ratio should ideallly be as much as 10:1. Third, the PPID must also not be asleep when T ~tion Mocle or ~/rPss~ing Mode me~ges are tran~mitt~A It can be assured that the PPID is awake when these m~s~g~s arrive by ~lesignin~ the overall PPID protocol in conjl~nr~ n with the frequency that the PPID gaes asleep.
An example of such a protocol design is shown below.
The second techniqul to assure that the PPID is asleep most of the time is to add an addition~l çlem~nt -- an RF Detector (701) -- to the PPID (FI~G. 7). The purpose of the RF Detector is to send a signal to the F~ SS~l (404) to awaken itwl~ne~,r the PPID is in the presence of an RF field. If the PPID is not in an RFfield; e.g., the PPID has been take:n out of the building for the evening, then the PPID
10 would not awaken until the PPID was re-introduced into the buil-ling This would clearly lead to con~iclerable savings in current drain. However, this techni,que has drawbacks as well. It would be s~raightforward and relatively inex~n~ive to design an RF Detector (701) capable of detecting a strong RF field. Ho~e~,r, a major advantage of the PPID is that it is capable of ~ ing weak RF signals, such as 15 those Downlink signals from the r~c~tion and/or l~r~ss~in~ modes. A device capable of de~;l;ng the presence of a weak RF signal would be eSsçnt~ y as complex as the combination of the Detector (402) diode and the ~mplifiPr (403).
This is equivalent to saying that the Detector (402) diode and Amplifier (403) are always awake, but the Processor ~404) is asleep until RF signals are hearcl. This 20 technique may not yield apprecialble savings beyond what is possible witll the "regular sleep time" technique outlined above. An ~ iti5~n~l problem with this approach is the following. When the PPID device is brought into a b~ i ng, sincethe entire b~ ing is covered by at least one Interrogator, the PPID woukl conl;nl.~lly be in an RF field, and thus continu~lly awake. To circumvent this 25 pl~bk.ll would involve a more complex RF Detector (402), which causes the :~ld-l;tion~l pl~bl~ s outlined above. However, for appli~tion~ in which the PPID is in an RF field only a small ~ ~ge of the time, this technique may be prcîel,cd.

Authorization and Scc.~
There are at least three techniques used for ~uthnri7~tion and s~ul;ly in 30 high-se~ y e-l./~olllllellls. One technique is to check "somP-thing you have in your po~essiQn", such as an employee badge. Another technique is to check ''s~methin~you know", which is typically im]pl~m~n~ as a ~ , PIN, etc. Another technique is "something about you", for ex~mple a picture, a voiceprint, a fin~,cl~l;nt, a retinal scan, etc.; th;s data is sometimes called "biometric data."

All three of these techniques can be applied to the use of the PPl[D. The PPID (400), itself, is the "something you have in your po~ç~iQn " Since the PPIDhas Pl~ hutton.~~ (such as 605), it would be possible for the employee to be required to enter a PIN into the PPID in o1der to, for eY~mI~ th~ri7P, initial bullding entry, S or ~llth~ri7~ entry into a particula,rly high security area. In an ~ltP!rn~te emb-Ylim~nt, the employee could use the PPID in the Interrogation Mode to be ic~entifi~A~ and then the employee could be required to type in a PIN on a keyboard, for example, located next to the doorway. Thus, the PlN is the "som~thing~ you know." Finally, the PPID
(400) could store the "somsthing about you." With the cost of memory decreasing, it 10 would be possible to have substantial amounts of Data Storage (420) on Ihe PPID
(400); for example, 32 kbytes of :EEPROM are possible in a single IC. A
co~ ,sed voiceprint or picture or other such data could be stored in less than 8kbytes. The PPID (400) would first be i~lentifi~A using the InterTogation Mode discussed above; then the M~s~~~ging Mode could be used to request the ~lata be 15 tr~n~~mitte~1 to the Interrogator. Ihis data could be then col~ d, using either con-l ut~r techniques or by a human being, with data taken from the employee; for example from a video camera, microphone, sc~nnin~~ station, etc. This would f~~ilit~te an entryway with full se~;wily, but withoul the presence of an on~utyse~wily person ~iC~te~ to this ell~yway. The se~wily person could be located in a 20 central security facility and support multiple enllywa~
One adclition~l elemçnt of s~;ulily involves the p~onql ~;u~ y of the employee in ~oi,se .~ion of the PP~ID (400). Let us assume that for some reason this employee encount~, an emergency con-lition It would be po~ibl- for d~e employee to enter a certain seq~lenre of data in the Pushbuttons (407) that in~ ate 25 an emergency cQn~lition Depencling on the sequence of data entered, ~ tion~l data co~ the nature of the emergency could also be entered. Upon receipt of the next Downlinlc Signal, regardless of which Mode, the PPID could transmit a m~-~ca~ co~ -~r data in~ ting the fact of the ellle.~,_.-cy awd also, optionally, the nature of the emergency. Thus, the Applin~tion~ Processor (l0l) could be 30 alerted, and the proper ~uthoritiçs could be alerted using the Commllni~ion~ Link ( 130).

PPID Operational ~p~ it;<~s We now outline how the PPID (400) could operate. As the el~ployee enters the buil~inp~ an Interrogator (103) mo~ . ;ng the entlance to the building 35 establishes radio commnnicatic-n!~ with the PPID th~ugh the use of the Interrogation Mode, and optionally transmits data to the PPID such as the time and/or l he date so that the PPlD is time-~yllcl~ lli~,d with the radio commllnicflti-)ne- systern. The Interrogator then reports to the Applications Processor (lOl) the fact that a specific PPID was interrogated, and an interrogation time stamp. Other Interrogat~rs throughout the building regularly ~ In~llu~,a~ion Mode Signals; when the S PPID is in range and receives such a signal, it ll~ s an uplink signal con~inin~
the m~nc~t~ry data as outlined ablove. Any other In~.lv~,ator (lO3) that ~;uccessfully communiC~tes with the PPID thrc~ugh the Int~.~atiorl Mode commlmicslte~e this fSact, along with the interrogation time stamp, back to the Appli~s~tion~ Pn~cessor (101). The.~fo~i, a time history of the l~ti~'n of a specific PPID is buill up in a 10 ~t~ ee, called the T OC~tioll Database (llO), in the ApplirfltiQnsp~vcessol. Since the errec~ive range of the Interrogation Mode is less than that of the ~ oc~ >n and M~osss~ing Modes, the .ls~ts~bs~e~ history of a spe~ific PPID will not be corltin~l~us~ in the sense that there will be periods of time in which the PPID is not in range of the Interrogation Mode. Thel~;ror~, the Interrogation Mode comm~ni~tion~ have 15 several results. First, the ~terrogation Mode is used to aUII~V1;~ initial e~ ce to the building. Second, the Interrogation Mode could also be used to autholi~
entrance to other doorways in the building, such as secure areas, etc.; the Interrogation Mode could also be used to ~llthon7ç el-t~n~e to the employee's office door. Third, the use of the Interrogation Mode by I~ v~lv~ througholJt the 20 buiklinp allows a time history, albeit not continuous, of the appl~ t~ location of a specific PPID.
Let us assume that the ~cation of a specific PPI13 (400) is d~sired. A
request for such a loc~tion is tr~n~:mitted to the Applic~tinn~ Processor (lOl) over a Commlmir~tion~ Link (130), which could be conntrt~d to the LAN, as sh,own in 2~ FIG. l, or ~lt~rn~tely could be coime~l~ directly to the Applic~tinn~ Processor (101). The ~rplication~ Process~r (lOl) first checks the T ~c~tion Database (l lO) to P wl.~_lh.,. the lor~tinn of the PPID (400) was r~nlly obtained. If no recent .. ".i. - ~~n of lor~tion was ma~ie, then the Applir~tion~ I~ocessor (101 ) d~ t~ eS that the loc~tion of this PPID is unknown, and a T oc~tion Mode Signal is 30 tr~n~mitte~l by all Interrog~tnrs, r~uesting the PPID to respond. If the loc~tion of the PPID was recently clete~mined, then in one emborlim~o-nt only Int~.lugi~t~ (103) in the vicinity of this previously d~t~ l.ined position could transmit a Location Mode Signal addressed to this specific PPID (400). Then, the Interrogators (103)transmit to the Applir~tion~ Proce,ssor (lOl) the results of the ~ ~c~tion Mode Signal;
35 whether a response signal was ~i~tected, and if so, the signal strength of that signal.
The Applications Processor (lOl) can then deLel..-il~ the a~pr~xi~ te locatinn of the PPID and return that information ItO the requester over the Comm~mi~tion~ Link CA 022l9075 l997-l0-27 (130).
Let us assume that a messQgt. is desired to be trQne-milt~l to a PPID
(400). The Applications E~ SSO1(1O1) receives such a request over the Comm-lnie~Q~tione Link (130), _nd stores the messqgç to be t~ ~ to the S ~ ;ate PPID in the ~leesQ~irlg DQtQb~ee (120). The Appli~Qtione Pr,xessor thenchecks the T oC~tion Database (110) to determine whether the lcc~tion of the PPID
(400) was recently obt_ine~ If no recent lle~ Qtion of loc~tion waS nlade, then the ApplirQti~ne~ OCeSSOl(lOl)d~t~ eS that the locatiQn of this PPII) is unknown, and a ~f~-ss~ing Mode: Signal is l~ ~l by all Interrogato]rs. If the 10 l~cation of the PPID (400) was recently detennine~, then in one embo iirtll~n~ only Intenrogators (103) in the vicinity of this previously det~rtnin~l po~ n could transmit a l~ss~ging Mode Signal addressed to this specific PPID (400). T~le PPID
(400) ~civcs the MPs~sging Mode Signal, and responds with an ackno~h lPA~m~nt m~seP,~, using MBS, to the Intenrogator. Thus, the "session" in this eA~nplc 15 consists only of the Downlink Mess~gn~ Mode Signal and the Uplink acknowledgnnent meSS~gf The Interrogator that l~cei~ s the achlowled~nent m-oS~ reports this to the Applic:ation Processor (101), which marks this mf-sc~ein the M~ss~ ing Database (120) as having been delivered.
Let us assume that dalta is desired to be received from a specific PPID
20 (400). The Applir~fion~ Processor (101) lece;ves such a request over the C'omm--J ir~tionc Link (130), and stores the request in the ~I~.cc~ing Database (120~. The Applir~tiorlc E~ocessc,r then checks the T ~tion Database (1].0) to dete~ i..c wh~ ~ the loc~tion of the PPID (400) was ~cel-lly obt~in~oA If no recent deterrnin~tion of loc~tion was ma~le, then the ~pplic~tionc Processor (10l.) 25 ~lete. .--h~es that the location of this PPID is unknown, and a ~ess~ ing M:ode Signal is ~ ~ by all Interrogators~ If the loc~tion of the PPID (400) was recently ~l~,t~ , then in one emboAim~nt only Interrogators (103) in the vicin:ity of this previously ~lf ~ ~ position could transmit a MPssq~ing Mode Signal addressed to this s~ifir PPID (400). The E'PID (400) lecei~,s the ~Irs~ging Mode Signal, 30 and respon l~ with an acknowledgment mes~g~o., which acknowledges receipt of the ~Il~S~q ing Mode Signal. This tran~ ~tion est~hli~hes the "session". The Interrogator (103) measures the signal strength of the acknowl~o~1gment m~se:~ge, and based on this signal strength, ~lett~rminrs what Uplink data rate can be ~up~l~d to this Tag. Commnnic~tions could lbe ~up~lled at a low data rate (for optil:num 35 range), or at a high data rate (for optimum data rate), depending on Uplink signal strength. The Interrogator (103) transmits another Mess~ging Mode Signal to the PPID (400), instructing the PPID which Uplink data rate to use in transmitting the ~ CA 02219075 1997-10-27 -required data. After this data is tr~n~mitt~A, this marks the end of the "session".
After the required data has been ~received by the Interrogator (103), the Interrogator L ~n~ the data to the Appliea~;on E~,cessor (101), which then tr~n~miit~ the data over the Commllnir~tirln~ Link (130). In an alternative embolim~nt the S Applir~tionc Processor (101) stolres the data in the ~ec~ jn~ Database ( 120) in the event the data is required later or in the event that the tr~nsmi~ion over the Cnmmllniratinn~ Link (130) fail8.
Let us assume that data is desired to be tr~n~ k~ to, and a] so ~received from, a specific PPID (400). Given the above ~lisc~sicn~ it should be clear how both 10 of these funetion~ could be incorporated into the same "session" between an Interrogator and a Tag.
Based on the Mess~frin~r Mode c~r~bility, the PPID (400) could be tr~n~mitted data, not for storage in the Data Storage (420) mo llll~ but for display on the Display (408). For example, the Appl;r~tion ~essor (101) could be ~ e~
15 through colnmllnic~tion~ over the Commlmir~ on~ Link (130), to transnlit a m~Ss~ to a particular PPID (4~) that the employee has lece;v~;d an urç~ent telephone call or an urgent electronic mail m~Ss~fJe Notifir~tion of the receipt of such a call or electronic mail m~ss~fre could be displayed on the Display (408). It may be helpful for the PPID (400) to alert the employee that a new m~ g~e is being 20 displayed on the Display (4:08). ',irhe PPID (400) could have an Alert Device (413) built in, which could be a buz~r (or other such sound maker) or vibrator.
An e~ctencion of the above Mes~gin ~ Mode sCçn~r o involves s~n~ g a meSS~f~re to a specific PPID (400)" having that m~seage displayed on the Oisplay(408), and requesting the employee to enter an acknowl~gmçnt into the :PPID (400) 25 in-1ir~tin~q~ that the employee saw the mess~ge. The ~ch-owl~d ment could, e.g., be entered by pressing a specific Pushbutton or Pushbuttons (4073. This would allowthe Arplir~tion~ Processor (101) to be certain that a critical mess~ was received.
In a high security e,~ on...-nt,~ddition~l prec~ution~ can be taken.
One technique is as follows. The Interrogation Mode is used to identify the PPID30 whose employee is requesting access to a gpecific e"l~yway. As fliscl1sse~ above, the MP.~in~ Mode is then used to request that data be ni~n~ back to Ihe Interrogator. If the required data is a PIN, then the employee must enter I he PIN into the PPID's (400) Pushbuttons (407); this PIN is then tr~n~mitt~ back to the Interrogator. If security of the PrN is an issue, that coll~lll~lllir~ti~n could easily be 35 encrypted. In the event that "something about you" was stored in the Data Storage (420) of the PPID (400), the Messaging Mode could be used to request that data be ~r~n~mitt~ from the PPID to the [nterrogator (103), and then l~n~ led to the Ap~ tinn.~ ~C~;ssol (101).
There are times in which the employee will not want to be loc~te~l The PPID (400) could be instructed, perhaps by the employee entering specific data into the Pushbuttons (407), to only respond to certain of the Modes of op~r~tilm~ or S ~ltPm~tely to not respond to any of the Modes of operation. For eY~m~ , the employee could use the PPID (400) to gain access to the bvildin~, but then disable the PPID (400) in this manner.
In a secul;Ly envi~ ent, howe~,~, employees surrender some ~ men of personal ~iv~;y. If the employee ~icql les the PPID (400), then the enlployee10 forfeits the ability to enter other controlled access e,.~ ways. Further, let us assume that we wish to monitor an entryway to assure ourselves that a person doe s not move past that spot without a valid PPID (400) being read. It is possible to inc~n~ c a motion det~ouction system to the Rl;ID system ~ here. In ~ddition~ it is pwci~le to incv.~.aLe motion detection capability into the In~.~ ator ( l03) 15 described here, with the ~rliti~m of a Motion Detector (220), which detects Doppler shifted signals in the audio frequency range. Theleron~, an Int~ ator (L03) could be confi~red to return an alarm ~ the Appli~ti- n~ Processor (101) in th~ event that motion was det~o~te~ but no PPID (400) was read.
Finally, in some very high security app~ on~ it may be required for 20 ~e Applin~tion~ Processor (101) ~,o "override" the ability of the employee to disable the PPID (400). For example, assume the three Modes of operation have two comm~n~l types; "System" level comm~n-l~ and "User" level comm~nf~ This is similar to certain cr~mm~nt1~ on a eOIIIpUt~,. syste~m ~c~uiling d ,. t lev~ls of a~lthnri7~tion The disabling of the PPID (400) by use of the Pl-~hbutton~ (407) 25 would not deactivate the PPID fully; but rather, could set the PPID in a mDde where it only respon-i~ to "System" level comm~n~l~ and not to "User" level comn~n~
This d~ on could be very hell?ful in a building envilol,ll,ellt in which certainparts of the building were at a much higher level of se~ulily than others, tl~e "User"
level comm~n(l~ could be used in areas of lower level of security, and the "System"
30 level comm~nd~ could be used in areas of high level of s~:u ily.
Among the meth~ls of powering the PPID ~liscus~ above, two metho l~ were an Energy Storage Device (411) and a Coil (412). These methods could be used together as follows. Assume that a Docking Station (800, FIG. 8) was developed. The PPID (400) wouhl be placed on top of the Docking Station (800) 3~ when the Energy Storage Device ~411) required charging. The Coil (412) of thePPID (400) would be oripnte~l so that it was directly on top of a similar Coil (801) in the Docking Station (800). Thus, the Energy Storage Device (411) could be re-charged Another helpful use of the Coil (412) would be to power the PP[D ~400) in the event that the Energy Storage Device (411), the Battery (409), or whatever method of powering was used failed to operate. This would allow the data in *he PPID (400) to be l~,co~ d even in *he event of such failure.
What has been described is merely illl,i,L~a~ of the applic~ti~ n of the principles of the present invention. Other ~ng~mPnte and methods can be impl~ment~fl by those skilled in *le art without de~ ;ng from the spirit and scope of the present invention.

Claims (21)

1. A communication device, comprising:
a demodulator of received modulated radio signals, operable for recovery of at least one First Information Signal;
a first decision element, responsive to the First Information Signal, adapted to provide an output that indicates a selected one of at least two alternative actions, to be referred to as Action A and Action B;
a display device adapted to display at least a portion of the First Information Signal;
a signal-generating device adapted to generate a Second Information Signal in response to the output of the decision element, wherein the Second Information Signal has a data rate, and said data rate is greater when Action A is indicated than when Action B is indicated; and a backscatter modulator adapted to modulate reflections of the received modulated radio signals, using the Second Information Signal.

2. The device of claim 1, further comprising:
a subcarrier signal generator, and a modulator adapted to modulate the subcarrier signal with the Second Information Signal, thereby to form a modulated subcarrier and wherein:
the backscatter modulator is adapted to modulate reflections of the received modulated radio signals with the modulated subcarrier.

3. The device of claim 2, wherein the modulator is responsive to the first decision element, such that the modulated subcarrier for Action B is a pure unmodulated tone at the frequency of said subcarrier.

4. The device of claim 1, further comprising at least one pushbutton, and wherein the signal-generating device is response to said at least one pushbutton, such that at least some contents of the Second Information Signal are determined, at least in part, by depression of at least one said pushbutton.

5. The device of claim 1, further comprising:
at least one pushbutton; and a second decision element adapted to provide an output that indicates whether the Second Information Signal should be transmitted and wherein:

the second decision element is responsive to at least one said pushbutton such that depression of at least one said pushbutton leads to an indication that the Second Information Signal should be transmitted.

6. The device of claim 1, further comprising an alarm, and means for activating the alarm based upon contents of the First Information Signal.

7. The device of claim 1, further comprising a storage medium for storing at least a portion of the First Information Signal.

8. The device of claim 1, further comprising means for generating at least a portion of the Second Information Signal from data stored within said communication device.

9. The device of claim 1, further comprising a stored record of biometric data pertaining to a holder of said communication device, and wherein the signal-generating device is adapted to include at least some of said data in the Second Information Signal.

10. The device of claim 1, further comprising:
an energy-transfer element; and an energy-storage element that is rechargable through the energy-transfer element.

11. The device of claim 10, wherein the energy-transfer element comprises a coil.

12. The device of claim 10, wherein the energy-storage element comprises a capacitor.

13. The device of claim 1, further comprising a solar cell and an energy storage device chargeable from the solar cell.

14. The device of claim 1, further comprising:
a signal processor having a sleep mode and a waking mode; and means for regularly awakening the processor from the sleep mode.

15. The device of claim 1, further comprising:
a signal processor having a sleep mode and a waking mode; and a radio-frequency (RF) detector, wherein:
the signal processor is responsive to the RF detector such that when the presence of an RF field is detected, the signal processor is awakened from the sleep mode.

16. The device of claim 1, further comprising:
a graphic; and an antenna at least partially situated beneath the graphic.

17. The device of claim 1, further comprising:
a graphic; and an energy transfer device at least partially situated beneath the graphic.

18. The device of claim 16 or claim 17, wherein the graphic is a picture of a holder of said communication device.

19. The device of claim 16 or claim 17, wherein the graphic is a company or organizational logo.

20. The device of claim 1, further comprising:
a plurality of pushbuttons constituting a mathematical keyboard; and a microprocessor in receiving relationship to the pushbuttons, the microprocessor adapted to perform at least some mathematical operations in response to manipulations of the pushbuttons, and to display results of such operations on the display device.

21. The device of claim 1, further comprising:
at least one pushbutton for designating an emergency mode; and means, responsive to the pushbutton, for executing an emergency mode upon receipt of the next First Information Signal after an emergency mode has been designated; wherein:

the signal-generating device is responsive to the emergency-mode executing means, such that when the emergency mode is executed, a Second Information Signal is generated containing data indicating an emergency condition.