CA1289622C - Code division multiplexed acknowledge back paging system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE An acknowledge back (ack-back) paging system is provided which includes a central station which transmits a group of message signals to an group of ack-back pagers which are addressed as a group. The users of the group of addressed ack-back pagers indicate a response to their respective papers thus providing ack-back data. The payers in the group of addressed ack-back pagers then simultaneously transmit back to the central station their ack-back signals using different respective pseudorandom code , a different pseudorandom code being dynamically allocated to each of the pagers in the group.

Description

96Z;2 ~M00523J
~nventor:
~azim~erz Siwiak ~ p m SIoN Mn~TIPL~E
acE~wI~~ ~AGlNG

~IE~ D~=
FIG. 1 is ~ block ~i~gr~ o~ ~ conv~ntl~n~1 display type ra~io p~ging ~y~tem.
FIG. 2 i6 ~ ~lock di~gra~ o~ ~he eck-~ac~ pagin~
~yste~ of ~he pre6ent ~nvention.
n . FIG. ~ ~ a block diagr~ of ~e cen~ral 6t~tion ~ploy~d ln ~h~ p~ging ~y~t~m of FIG~ ~.
FIG. 4~ ~ a t~e v~. ~vent represent~ti~ of th~ tran~ sion fro~ the central ~ation of ~he ~y~tem og the ~nvention.
FIG. 4B i~ a repre6entation o~ ~n addre~ bloc~.
u~d in the paging protscol of the paging 6y~em ~f the ~nv~ntion.
FI~. ~C is ~ r~pre6entAtion o~ a ~es~age block uied in the pagin~ pr~tocol of th~ paqing ~y~t~ of

2 0 t:he inve~nt~on .
F~C. ~D $- ~ tl~ v~. ~v~nt rspr~B~ntati~n of tho rac~iv~r portion of th- c~ntr~l ~tationr ~ E i6 a t~m~ vant repr~s~ntation of the activity o~ a~k~aok pagQr AB-l.
FI~. ~F i~ ~ t~e v~. ~vent r~pr~entation o~
the ~¢tivity o~ ~ck ~ck p~ger AB-2.
~ IC. 4G ls a tl~ v8. ~vent repre~Qntation of ~he act~v~ty o~ ack-~ack pager A~-M.

. ' ~b ~ - .

, . , ; : ' .

~L2~22 FIG. ~H i~ ~ time ~6. ~vent r~pr~6ent~tion of the acti~ity of ~ non ack-bac~ pager in the paging g;y~tem o~ the ln~entiDn.
F~G. 41 îs a time ~ sYent repre~;~nt~ti~n o~
5 the ~eti~ity of am lmp~ged ~ck-b3ck p~ger iLn ~e p~ging 8ylS1:eDI o ~e ~nventi~n.
FIG, 5 i6 ~ flow~h~ epi~:ting t~e operation of the oQntr~l ~;t~tion ln the paging ~y~te!m c~f the invention.
FIC. 6 loe ~ bloc)c ~iagr~m of one o~ ~he ac3c-back p~gers employed in ~e paging ~y~te~ o~ ~he invention.
F~G. 7 i~ pseudc~r~ndo~ ~PN) code l~ok-up table e~ployed by t~e ~t:k~ack pager~ ln ~he ~sy~tem o~ the ~.nven~n-FIG. 8 ~s g~ wcha:rt of the operation o~ the ack-back pagers of ~he paginy isy~te~ ~f the invention.

2 0 1BACRGRO~ND OF l~lPVEN~I~

Thi~ ~nvention relates in general to radio t:on~unications ~yst~s. M~re particularly, the ~nvention relate~ to r~dic~ paging ~ystem~.
In tl~e pa~t ~ev~ral year~, radio p~ging technology ~a& ~dvanced froD the rather ~imple ~one-only pager (tone al~ nly, no vo~ce), 1:o the tone and voice pag~r ~ton~ rt with a voice D~essage) and more rec~ntly to t~ ~lph~nu~neric di~play pager.
In ~ typical c:onventional alphanumeric di~pl~y paging ~y~t~ ~uc~ ~s th~t ~hown B5 ~y~tem l0 in FIG. 1, a central transmi~tex or paging t~r~inal Z~ i6 u6ed to gen~rate the r~dio pages which ~re tran6mitte~ via a ra~ link to ~ fl~!et of paging r~ceive~s l, 2, 3 ,~ . .

: :
~ , ~

~g~

..~,N, wberein ~ i8 the tctal n~a~ber o~ psger6 in ~y~t~ 10. A uni~ue digit~l ~ddre~ ~6 ~ oc~ted with each c~P p~ g receiv~r~ 1, 2, 3.".N. ~ p~ge which is trans~i~t~d by p~ging ter~inal 20 consis~s 5 of the unique di~itally ~ncoded addr~ O:e the particul~r pager to wh~ch the page i~; t~rgeted, immedi~tely followed by ~ corresponding digitally encGded numeric or alp~numeric pasJe ~Des age which is ~ntended for di~pl~y on the target p~c3er.
~ cally, the ~umeric or alphanumeric p~ge message ~ store~ in ~ memory wit21in the paging recei~er ~or later recall and di~;play by the p2ger user. Paging rece~ver~ are ~vail ~le with a wide rang~ of mes~ge ~tor~ge capabilitie~ wh~oll r~nge 15 fro~ e ability to 6tore ~u6t ~ few rather ~hort numeric p~ge ~e sage6 to t~ abil~ty tv ~;tore a r~lst~vely large number o~ longer ~lphanumeric p~ge s~es~ages .
~owever, Il:onvention~l d~ ~play paging ~ygte~s are 2û generally one way ~y~te~. ~rhat i6, the user receives a paging me~i~age from the central terminal ~ut ha~ no w~y of re~ponding to th~t ~es~age with his or her pager. Instead, the p~ger u6er ~ust ~eek out telephone or ~>ther ~e~ns of r~ps:nding to the origin3tor OI the pagins me~sage.

, ~R~Y QP ~ II~Y~1!2~

Acc:ordin5~1yt it iB one ob~ct of the pre~ent lnv~ntion i~ to prov~d~ paging syl;t~m in which the r~dio pager 1~ capabl~ o~ r~sponding bacJc to the p~ging t~r~inal and the ealler.
~nc>ther ob~t of the pre~nt inv~ntion is to 3S provide 2 ra~o p~ging ~y~t~m in whioh a group of addre~E;eZ p~ger~ ~re G~pable o~ IGi~ultaneously tran6mitting acknowle~ge balck 6$gna~ on ~ ~ele~ted ~requency, e~ch pager tranE;mi~ting a r~gpecti~e achlowledge back ~E;ign~l u ing e~ differerlt 5 ~ anti~llly c~rthogonal pseud~r~ndom ood~.
In one ~mbodi~nt o~ the ~r~vention, ~
~cknowledge ~ack p~ger ~ ~provided which h~s a unique ~ddre~ a~socinte~ 1therewith. The~ p~ger includes a rece~ver for rec~iving pagi~ ~ignal~ :Erom a c~ntral 10 zt~tion. The paging signals including a b~tch o~
pager addresse6 transmitted in ~ 6eguenti~1 order durins~ a ~irst time period, wherein l~ 6 the number o~E pager e~ddress2s ~n t~e }~atch. The pager further includes ~ dec:oder, ¢oupled to the r~ceiver, ~or 15 detectins the presence o~ the pager ' 6 addre~ withi:n t~e lb~tch s~f ~ ddre6æQ6. The pager includ~ an addre~ order ~eter~inis~g app~ratus, coupled to the dect~d~ng ~¢an~, ~or d~tennining the order o~ the pager'~ ~ddre~ w~t~i.n tb~ ~atch o~ ~S a~dre~se~. ~rhe pager ~urther i.nclude~ a p~eudorando~ cc~de tran6mitter or tran mittinr~ ~n ~cknowledge bsc~c ~ignal at a ~ cted fr~ ncy, EUC~ ackllowledge back ~ignal including ~ sel~cte~ 2n~ of a plurality of M
subst~ntially o~c~gonal pseudor~nd~ code~. The 25 ~lect~d one o~ des ~xhibitc a pr~deter~nined r~lat~on~hip to the order o~E ~he addre~ of l:he payer within ~he b~tch of IS addre~se6.
~ he f~ature~ o~ th~ in~ention ~eli~ved to be nov~l 3~ Gpaciii~lly ~at ~orth ~n the ~ppended cl~i~a~ ~ow~ver, th~ ~ m ~ntio~ its~lr, both ~ tv its ~tructur~ and ~ethod o~ operation, ~ay best ~e under~too~ by r~rr1ng to the f~llowing ~scription and the ~ccompnnylng draw~ngs.

"~
' . ~ , , : ~ ,, ~L2~ 2 DETAILED DES~RIPTION OF THE INVEN~ION

FIG. 2 is a simplified block diagram of the acknowledge back paging system 100 of the present invention. Paging 6y~tem 100 includes a central station or paging ter~inal 110 which is capable of both transmitting outgoing paging signals and of receiving acXnowledge back (ack-back) paging signals.
Paging sy6tem 100 includes a plurality of ack-back pagers 121, 122... P, wherein P is t~he total number of ack-back pagers in the pager population of system 100. Each of ack-back pagers 121, 122...P has the capability of receiving paging signals from central station 110 and of permitting the pager user to respond to such paging signals. That is, pagers 121, 122...P permit the user to reply or acknowledge back to a page from central station 110. It is noted that conventional non ack-back pagers such as pager 130 are also includable in system 100. In FIG. 2, double arrows between central station 110 and each of acX-back pagers 121, 122...P are used to denote that two way co~munication exists betwsen central ststion 110 and such ack-back pagers. A single arrow deno~es that only one way communication exists between station 110 and pager 130.
FIG. 3 is a more detailed block diagram of central station or paging terminal 110. Central 6tation 110 includes a conventional telephone inter~ace 140 of the type generally used for central paging terminals. Telephone interface 140 couples outside telephone lines 141, 142, etc. to an input 150A of a microcomputer 150. Telephone interface 140 converts message signals from lines 141, 142, etc. to digital signals which microcomputer 150 can process.
For example, a caller wishing to send an alphanumeric . .. . . .. . . .

~2~3~6~2 page to an ack-back pager user uses dual tone multi frequency (DTMF) to key in a desired message.
Telephone interface 140 then converts such analog DTMF alphanumeric message to its digital equivalent which microcomputer 150 processes a~ discussed later in more detail. Central station 110 further includes a keyboard 160 coupled to a data input 150B of ~icrocomputer 150. Keyboard 160 permits an operator to directly input messages into mic.ro~omputer 150 for transmi~sion to pager~ within the pager population7 A read only memory (ROM) 170 i~ coupled to a memory port 150C o~ microcomputer 150. ROM 170 includes a control program which controls the operation of microcomputer 150 and the circuits coupled thereto. A random access memory (RAM) 180 is coupled to a memory port 150D microcomputer 150. RAM
180 provides temporary 6torage space for microcomputer 150 a~ it carries out the instructions of the control program within ROM 170~
When a paging ~essage and the identity of the particular pager ts be addres~ed are provided to microcomputer 150, the contxol program causes ~icrocomputer 150 to generate digital paging signals at it~ output 150E according tG the protocol later described. Microcomputer output 150E is coupled via a level shifter 190 to the input of a transmitter 200. The output of tran~mitter 200 is coupled to an antenna 210 having dimensions and characteri~tics appropriate to the particular paging frequency chann21 selected for the operation of central station 110. Level shi~ter 190 ~erve~ to adjust the 6ignal level o~ the paging signals generated at microcomputer output 150E to a level appropriate for the input of tran~mitter 200.

.

12~ 2 For purposes of this exampley it will be assumed that ack back pagers 121, 122-P are acknowledging back via phase shi~t keyed (PSK) digital modulation.
Those skilled in the art will appreciate that other forms of modulation as well may be e~ployed by ~cknowledge back pagers 121, 122 P to respond to the paginy ~ignals transmitted by central station 110.
In such a PSK embodiment, central station 110 includes a receive anténna 220 for receiving the ack-back signal~ transmitted by ack-baclc pagers 121, 122-P. In actual practice, antenna 210 may also be employed as antenna 220. Receive antenna 220 is coupled to the input of a PSK receiver 230 which includes an in-phase (I) output 230A and a quadrature ~Q) output 230B. Receiver output~ 230A and 230B are raspectively connected to inputs 240A and 240B of digital signal processor 240. One digital signal processor which may be ~mployed as proces or 240 i5 the model DSP56000 ma~u~actured by Motorola, Inc.
Digital signal processor 240 includes a control input 240C which is coupled to a control output 150F of microcomputer 150 to permit microcomputer 150 to control processor 240. Digital signal processor 240 urther includes a data output 24OD which is coupled to the data input 150G of microcomputer 150~ Thus, it is seen that digital signal processor 240 decodes the digital data received at the I and Q inputs 24OA
and 240B thereof and tran~forms such information into digital data which i~ provided to microcomputer clata input 150G.
FIG.'s 4A-4I are timing diagrams which show the signaling protocol employed by central station 110 and ack-back pagers 121, 122-P~ More specifically, FIG. 4A is a simplified timing diagram of the paging protocol transmitted by central station 110. In FIG.

.

~;~896~

4A, time is represented on the horizontal axis and respective events are denoted as they occur at designated points in time along such time axis.
Central station 110 first transmits a pream~le signal 300 during a time interval Tl. In one e~bodiment, preamble s~mbol 300 consists of a plurality of alternating 0~8 ~nd l's transmitted for a duration of time T1. For example, preamble symbol is a 010101...
signal.
In accordance with the present invention, central station 110 groups paging addresses into groups of M wherein M is the number of paging addresses in a particular group. For purposes o~ -thi~ example, and not by way of limitation, the nu~ber of paging addresses and thus the number o~E
messages corresponding to such addresses is selected to be 20 (that is, M=20). That is, as messages are called into central tation 110 via telephone interface 140 or keyboard 160, such p~ging messages and corresponding address information are held or stored in RAM 180 until a group of up to M=20 messages has been provided to station 110. In alternative embodiments of the invention, non ack-back pages may be interspersed with ack-back pages to increase the efficient throuqhput of the paging ystem if desired as will be discussed later. The group of M=20 ack-back pager~ is a subgroup of the overall population of P pagers. Once station ~10 has received 20 or M paging messages, microcomputer 150 aequentially transmits the 20 corresponding addresses as a group 310 during a time interva~ T2 subsequent to time interval Tl as shown in FIG. 4A.
FIG. 4B show0 the sequential relationship of each of the addresses within group 310. The address of the ~irst p~ger of the group of M pagers to be . . .
:

, , ;
.

362~ -addressed is designated address 1 and is transmitted first in group 310 as shown. The pager to which address 1 corresponds i~ designated AB-l for reference. The address of second pager of the group of M selected ack-back pager~ i~ designated address 2 and is transmitted immediately following address 1 The pager to which address 2 corresponds is designated pager AB-2. This process of address trans~ission continues seguentially in the same ~0 fashion until all of the addresses of the group of M
pagers are transmitted ending with address M, the address of the last or M'th pager in group 310. The pager to which address M corresponds i8 designated pager AB-M. A non-ack back pager AB-3 is shown addressed in ~he block of M pages as will be described later in khe discussion of FIG. 4~.
In one e~bodi~ent of the invention, the duration of time during which preamble signal 300 is transmitted, namely T1, is approximately equal to 10 msec. Those skilled in the art will appreciat~ that Tl may have values greater than or less than 10 msec providing Tl iB sufficiently long to permit the ack-back receivers 121, 122~..P to ~ynchronize to the paging signalR transmit~ed by central station 110.
~pparatus for synchronizing paging receivers to paging ~ignals is well known to those skilled in the art and is included in àck-back pagers 121, 122...P~
For purpo~es o~ example, the time duration ~r2 of the group 310 of ~ddresses is s21ected to be approximately equal to 1 sec. Those skilled in the art will appreciate that T2 may actually be greater or less than 1 sec depending upon the number of paging addresses M selected to be in the group 310 and the frequency of transmission of the digital data comprising such paging addresses. The selection of ' .

1 2~99E~ZZ

the time period T2 in this example should not be taken as in any way limiting the invention. To reiterate, the particular pagers of the population P
which are addressed in address block 310 are designated as pagers AB-l (the first pager to be addressed), pager AB-2 (the second pager to be addressed)...pager AB-~ (the last pager addressed of the group of M pagers).
After transmis~ion of the group of M addresses, central 6tation 110 transmit6 a reference carrier signal at a ~requency FRX at 320 during a time interval T3 following time interval T2. Subsequent to transmission of reference carrier 320, central station 110 sequentially transmits the 20 paging messages corresponding to the 20 paging addresses of address group or block 310. More specifically, thsse M or 20 data ~essages are ~ent as a group or block 330 of messages. Each of the ~ messages in block 330 bears a predetermined relationship to the order of the pager addresses in block 310. For example, in one embodiment of the invention and a~ shown more clearly in FIG. 4C, message block 330 includes message 1 data followed in time by an end of message (EOM) field. The EOM ~ield of ~essage 1 is followed sequentially in time by the message 2 data which is in turn foIlowed by another EOM field. The process of sending the respective mes~ages 3, 4, etc. within me~sage block 330 continues until mes6age M is transmitted followed by a respective EOM field as shown in FIG. 4C.
In the em~odiment of the invention described above, the predetermined relationship between the ~equence of mes~ages transmittad in message block 330 and the ~equence of pager addresses transmitted in address block 310, is conveniently selected such that . .
,- ' `' ' ' , ~2~ i2;2 address 1 is first transmitted in block 310 and the message 1 corresponding to such address 1 is transmitted first in the later following message block 330 occurring during time slot T4. To illustrate this predetermined relationship further, address 2 i8 transmitted second, that i~ immediately after address 1 in address block 310.
Correspondingly, in the later following time slot T4, message 2 is transmitted second, that is, immediately following message 1' EOM field. The same relationship exists between the remaining addresses in block 310 and messages in block 330.
The invention, however, is not limited to the particular predetermined relationship described above between the sequence of pager addresses in address ~lock 310 and corresponding messages in message block 330. For example, in another embodiment o~ the invention, the sequence of pager addresses would : remain as illustrated in FIG. 4B with address 1 being sent first followed by address 2 and ~o forth until address N i transmitted completing the block.
However, the sequential order in which the me~sages in message block 330 are transmitted in such embodiment may commence with trans~ission of mes~age M first followed by message M-l (or message 19) ~ollowed by message M-2 (18) and so forth until message 1 is fina}ly transmitted at the end o~
message block 310. (EOM ~ields are still situated between message~.) What is important here is that a predetermined relationship exists between the order in which the paging addresses are transmitted in address block 310 to the order in which the paging ~essages are transmitted in message block 330 so as to permit acknowledge back pagers AB-1, AB-2,...AB-M
to match a particular mes~age within block 330 to a , .

~;~89~22 respective pagin~ address of block 310. This enables a particular pager to determine which of the 20 paging messages in block 330 is intended for it, as will be discussed subsequently in more detail.
Although examples have been discussed above wherein the predetermined relationship bet~een the order of the pager addresse~ of addres-~ block 310 and the paging messages of me~sage block 330 are both ascending, and in the other example ascending/descending, those skilled in the art will appreciate that an ~rbitrary relationship between the paging addresses on block 310 and the paging messages o~ block 330 may al~o be selected as long as this predeter~ined known relationship is programmed into acknowledge back pager~ 121, 122... P.
A reference carrier exhibiting a ~requency of FRX is generatad during a period of ti~e ~3 subsequent to the end of transmission of the pager addre~ses in addre~s block 3107 In one embodiment of the invention, T3 i8 equal to approximately 70 msec.
Those skilled in the art will appreciate that T3 may be longer or shorter than 70 msec providing the re~erence carrier shown at 320 exhibits a time duration ~ufficiently long t~ enable freguency determin~ng circuitry, later described, in ack-back pagers lZ1, 122...P to determine the frequency of reference carrier 320.
FI5. 4D i~ a time v~. event diagram of the status o~ receiver 230 in central ~tation 110.
Sukse~uent to time period T~, receiver 230 at central station 110 is turned on to receive ack-back signals from the 20 pagers in the group of ~ during a time period T5. Each of the group of M ack-back message signals transmitted by the respective ack back pagers in the group of M employ a different respective ,:
, , ' ~g~2 pseudorandom code within a common freguency channel as will be discussed in more detail ~ubsequently.
Receiver 230 is thus capable of distinguishing and decoding message signal~; coded with each of the 20 or 5 M different pseudorandom codes. The configuration and operation o~ receiver 230 i~ discussed in more detail la~er.
FIG. 4E i~ a time versus event diagram for the status of ack-back pager AB-l, that is, the ~irs~
addresfied pager of the group of ~ pagers. FIG. 4E is drawn to the aame time scale as FIG. 4A. Durin~ the Tl ti~e interval, pager AB-l receives the preamble at 340. During the following time period T2, pager AB-l receives and decodes address 1, which in this example is the address of pager AB-l. It is noted that p~ior to reception of the pr~amble at 340, pager AB-l is in a ~sleep~ or ~battery saver~ state. That i9, prior to such Tl time period, pager AB-l and the other pagers of the population of P pager~, have several of their power consuming circuit~ turned o~f or placed in low power consumption ~tates. Those ~killed in the art are already familiar with the powering down of radio pager circuits in order to achieve ~attery saving and thus exactly which circuits in the pager are powered down, and the d~gree to which they are powered down, are not discussed here in detail. What is i~portant, however, is that the ack-back pagers o~
the population o~ P pager6 ar~ placed in a ~battery saving~ state or ~leep state~ during prescribed periods of time ~uch aa that mentioned above and which will be later apecified.
When pager AB-l receives the preamble 340 during time period T1, pager AB-l i6 6witched from a battery saving 6tate to a fully operational 6tate such tbat pager AB~ capable of receiving .

. . , . , , , , . ~ ~ -, .
, ~

information transmitted thereto. That is, subsequent to reception of the preamble at 340, pager AB-1 is fully turned on such that pager AB-l receive~ and decodes its addres6 at 350 at the beginning of the T2 time period. In onP embodiment of the invention, pager AB-l conveniently returns to the n~leep state~
for the remainder of the T2 time period during which pager addre~ses are transmitted. Prior to receiving the reference carrier FRX at time period T3, pager AB-l is returned from the ~61eep state~ to the fully operational state. Upon receptlon of the re~erence carrier, FRX at 360, pager AB-1 determi~es the frequency of cuch carrier in a man~er described in more detail subsequently.
Re~erring to FIG. 4E, in conjunction with 4C, it is seen that the mes~age 1 tran~mitted during time period T4 at 370 i~ rec~ived by pager AB-l at 380 as shown in FIG. 4E. Pager AB-l receives message 1 at 380 and matches message 1 to addre~s 1. That is, by means later described in more detail, pager AB~1 is progra~med to datermine that message 1 is the particular message of the group of ~ messages which i~ intended ~or pager AB-1. Sub~equent to reception and display of message 1 at 380 a6 shown in FIG. 4E, the user of pager AB-1 indicates his or her response to mefi~age 1 during a time period T6 at 385. Ti~e period T6 is not drawn to ~cale with respect to the other time pexiods di~cussed. Time period T6 is sufficiently long to permit indication o~ a response by the pager user. Subsequent to time period T6, pagers AB-l, AB-2 ... AB-M simultaneously transmit acknowledge back signals with respective pseudorandom code~ back to central ~ation 110 as at 390 during a time period T5. Subsequent to the ack-back transmission at 390, pagers AB-l, AB-2 ... A~-M are ... . . . .. .. .. ..

" ~ .': ' ' . :
, , ~ ;
', ,, :L2~ 2 placed in the ~sleep state~ unti~ awaXened again by a preamble as at 340. In an alternative embodiment of the invention, ack-back pagers AB l...AB-20 reply back automatically without action by the pager user.
In such an embodiment, prior to being paged, the user preselect6 a reply already stored in the pager or key~ into the pager a predeter~ined message which the pager usefi a~ the ack back reply wh,en it is later addres~ed by central ~tation 110. For example, the ack-back pager user sQlect~ a ~not available~
respon~e or otherwi~e keys into the payer a ~not available~ response when the pager user wishes to inform callers into central station 110 that the pager user i6 not taking any calls currently.
Clearly, the reply data may be provided to the ack-back pag~rs in many different ways. In the case of a user selectable response already programmed into the pager, time period T6 can be arbitrarily short, that is just ~ufficiently long enough to psrmit transmission of 8UC~ a selectable response whose length i6 predetermined and known to the microcomputer 150 in central st~tion 110.
FIG. 4F is a time versu~ event diagram oP the status of ack-baok pager AB-2, that is, the second pager addressed of the group of M ack-back pagers.
Pager AB-2 receives the preamble at 340 and then switch~s from a ~sleep ~tate~ to a fully turned on state. Pager A~-2 receives address 1 (the address of pager AB-1) at 350. Pager AB-2 decodes such address 1 at 350 and determines that the decoded address is not its own address. At 400, pager AB-2 receives its own address, namely address 2. Pager AB-2 decodes and determines that address 2 is its own address. As with pager A~-l o~ FIG. 4E, pager A~-2 o~ FIG. 4F
goes to the ~sleep ~tate~ for the remainder of the T2 , . ' ' ~ ' ~
, `.; ' , ~ `, . ' ~L2~ 22 time period. Pager AB~2 nwakes up~ in time for reception of the reference carrier FRX at 360 during time period T3. As seen by examining FIG. 4F in c~njunction with FIG. 4C, pager AB-2 receives the 5 AB-1 page data transmitted at 370 within time period T4. As explained in more detail subseguently, pager AB-2 determines that the AB~l message data i8 not a match. That i6, pager AB-2 deter~ine that the pager AB-l message data (meeeage 1) is not intended for pager AB-2. After the end of message (EOM) marker following me~sage 1, pager AB-2 receives the AB-2 message data (message 2) at 410 within time per-od T4. Pager AB-2 determines that the message 2 data at 410 i8 a match and that such message 2 data is intended for AB-2. The mes~age 2 data is then displayed to the user of pager AB-2 who indicates an acknowledge back response to pager AB-2 during time period T6 at 415. During the sub~equent time period T5, the acknowledge back message is sent to central station 110. Such ack-back messag~ is codes with a second pseudorandom code different from the fir~t p eudorandom code with which pager AB-1 codes ack-bacX 6ignals. Subsequent to transmis6ion of the acknowledge back respon~e at time period T5, pager AB-2 i~ caused to go to sleep.
FIG. 4G is a time versus event diagram of the stakus of ack-back pager AB-M, the last of the group of M pagers to be addressed. Pager AB-M receives the pr~amble at 3~0 to ~witch it ~rom a ~battery saver state~ to a fully operational state. Pager AB-M then receives the 1~ addresses of the other pagers in the group o~ M, such as at 350 and 400 until finally pager AE-~ receive~ and decodes its own address a~
420. Pager AB-M is thus ~ignaled that a message for it will be transmitted momentarily. Pager AB-M

, . . . . .
', . .

,~ ., . :

~2~ 2 receives the reference carrier signal FRX at 360.
Referring to FIG. 4G in conjunction with FIG. 4C, it is seen that pager AB-M receives message 1, message 2 ...message M l and determines that all of these messages are not matches. That is, such page data messages are not intended for AB-M. Pager AB-M
receives the page data message M transmitted at 430 (FIG. 4Cl and received at 440 (FIG. 4G) within time period T4. Pager AB-M determines that such message M
at 440 is intended for pager AB-M and di6plays the contents as such me6sage M to the pager user. During time period T6 at 41S, the pager user supplies acX-back pager AB-M with an acknowledge back response.
During the subsequent time period T5, pa~er AB-M
sends such acknowledge back response back to the central station 110 with a pseudorandom code M at 450 different from the pseu~orandom codes with which the remaining ack-back p~ger~ AB-l, AB-2 ... AB-~M-l) code their trans~issions. Subsequent to the transmis~ion of the ack-back response at 450 during time period T5, pager AB-M switches to the ~sleep state~.
one embodiment of the invention accommodates the ituation where one or more of pagers within the ~roup of M payers are not ack back pagers. For example, it will be a~sumed that pager AB-3 ig not a pager with acknowl~dge back capability, but rather is an alphanumeric display pager which operates as shown in the time versus status diagram of FIG. 4H. Non ack-back pager AB-3 receives a preamble at 340 which causes pager AB-3 to ~witch from a ~sleep state~ to a fully operational state. Subsequent to reception of the preamble at 340, non ack-back pager AB-3 receives addres6 1 at 350 and addr~ss Z at 400 during time interval T2. In this particular example, it is , ~
" ' ,, ' ' '' ` ' " `

~2~g622 assumed that pager AB-3 is the third pager addressed within time interval T2. That i~, address 3 is the address which corre~ponds to pager AB-3. Pager AB 3 receives addres~ 3 within time interval T2 at 46~ as shown in FIG. 4~, Pager AB-3 decodes address 3 and determines that pager AB-3 has been paged and that a page data message will be transmitted to it shortly.
Non ack-back pager AB-3 i~ activated to an ~awake state~ during time interval T4. Pager AB-3 then locates the particular AB-3 page mes~age which i~
intended for it within time period T~. That is, since the predetermined relationship between the order of the pa~e messages transmitted within time period T4 is known by pager AB-3 wlth respect to the order of the addre~se~ transmitted within a time period T2, pager AB 3 locates or matches the AB-3 page data message at 470 in a manner similar to that employed by the re~aining pager~ within the group of M. For example, in this embodiment of the invention, since pager AB-3 was the third pager to be addressed in the group of ~ pagers, pager AB-3 will expect its message to likewise be third in the sequence of messages with message block 330 (FIG. 4A) or more specifically at 470 of FIg. 4H. Once message 3 is so selected, pager AB-3 displays message 3 to the pager user. In thi~ particular embodiment, the pager user does not have the option to transmit a response back to the central ~tation 110. Thus, non ack-back pager A~ 3 iB switched to a ~sleep fitata~ after the AB 3 message corresponding thereto has been received.
FIG. 4I $s a time versus event diagram of the statu6 of an unpaged ack-back pager of the population of ack-back pagers 121, 122,..~P. That i~, FIG. 4I
illustratas what occur~ when an ack-back pager receives and decodes addresses which do not .. . .
.. ~......... , . ~ .
. - . - .
: .
~: ' .
, ,` . ' ~ ' .' ' .

~96Z2 correspond to the unique address of such unpaged pager. More specifically, the unpaged pager, which is referred to as pager AB-U, receives the preamble signal at 340 and switches from a ~sleep state~ to a fully operational state. Pager AB-U then proceeds to receive a group of M or 20 pager addresses at 480 during time interval T2. Pager AB--U fails to find its address within that group of M addre~ses~ Thus, after time period T2, pager AB-U returns to the ~sleep etate~ where it will remain where it will remained for a predetermined period of time.
Alternatively, at the end of addre6s block 480, a ~go to 61eep~ signal can be transmitted to all pagers which did not receive a valid address to cause ~uch pagers to enter the ~leep state. FIG. 4I also represents the time versus event status of an unpaged non ack-back pager.
FIG. 5 i~ a flow chart of the control program which is resident in ROM 17~ of central station 110 This control program control~ the operatio~ of microcomputer 150 in the manner which follows. The flow chart o~ FIG. 5 summarizes the operation of central ~tation 110 which was de~cribed above in the discusRion of the signalling protocol illustrated in FIG's. 4A - 4I. In accordance with block 5~0 of the flow chart of FIG. 5, ~icrocomputer 150 i~ subjected to a power-on reset when it i~ turned on. That :is, syste~ variable~ are initiali~ed at that point in time. For example, M, which iB the number of ack-back pager~ $n a particular group is initialize~ at apredetermined number, for example 20. Additionally, a message counter variable, I, is initialized at a value of O in block 500. Once initialized, central station 110 i6 ready to accept messages from telephone callers ~nto interface 140 or from a system .. . .

. :
. . .
' ~
. . . .1 , , .

~2 !3~

operator at keyboard 160 as per block 510. When a message for a particular pager user i nput into central station 110, such message is stored in RAM
180 together with indicia of the particular pager ~or which such mes~age is intended as per block 520.
Such message is counted by incrementing the message counter variable I by the quantity 1 as per blocX
530. Microcomputer 150 then make~ a determination as to whether the number o message~ w~lich have been collected and stored in memory is ec~al to M or 20 in this cxample. That i8, as per decision block 540, microcomputer 150 determines whether message counter I equals M. If the me~sage counter I does not ec~al M, which signifies that a group of M messages have not yet been fully collected, then flow continues to block 545 where a determination i6 made whether or not a time out of T0, for example TO = 10 ec, has been exceeded. If the time out ha not be2n exceeded, then ~low continues back to input block 510 to await input oP yet another message. If in block 545 it determined that the time out has been exceeded, then a preamble signal i~ transmi~ted at block 550. This time out feature is provided such the microcomputer 150 will not have to wait ~or long periods of time for a queue of M mes~ages to be collected prior to transmitting such ~essages. I~
prior to expiration of the time out, it is determined that me~sage counter I does equal M at block 540, then transmi~sion of the preamble ~ignal i5 commenced ~0 at blo~k 550.
Microcomputer 150 then looks up and retrieves from memory the addresses whiah correspond to each of the group of ~ pager6 as seen at block 560. The addresses within such group of M pagers are sequentially tran~mitted in a predetermined order, , .. . . ... . . . .
. ' .. - , :' . . :
- . ~ '~ ' " ' ' , 3L2~ 2 ~or example, ~irst in last out' or ~Pirst in first out~, as per ~ubsequent blocks 570 through 610. More specifically, counter I is reset to 1 and now functions as an addres~ counter as per block 570.
Address I i~ retrieved from me~ory ac per block 580.
That i8, in the first time through the loop starting at 580, since I - 1, address l iB retrieved from memory. That is, ~icrocomputer 150 Iooks up the particular pager address which corresponds to the pager for which message l is intende~. ~ddress l is then transmitted as per block 590. At deci6ion block 600, microcomputer 150 makes a determination of whether or not all M addresses of the group of M
addre~ses corresponding to the M messages have been transmitted. Thi~ i8 detenmined by ~icrocomputer 150 calculating whether or not I i equal to M. If address cou~ter I is not equal to M, then all 20 addres~es have not been transmitted and I is then incremented by l a~ per block 610. Flow then continu~s back t~ block 580 at which the next address of the group of M=20 addresses i~ retrieved from memory. Thi~ process continue~ until I = M at block 600 which ~ignifies that all 20 addres~es have been retrieved and ~equentially transmitted as a group.
Flow then continue to block 620 at which reference carrier F~ is transmitted.
Counter I i~ then re6et to I = 1 as per block 630. Counter I i8 now ~mployed a~ a message counter again in the s~sequent portion o ~he flow chart of FIG. 5. Message I i~ retrieved from memory at block 640. The first time through the loop starting at block 640, I iB equal to 1 and thus mes6aye number 1 is retrieved at block 640 the first time through such l~op. Nessage I, or in thi~ case ma~a~e 1, is then transmitted by central station 1~ a~ per block 650.

.. .
`
- .
. :
~, . ~ .
.~ . .
.
'' ~ ' ' .

~g622 An end of message (EOM~ marker is transmitted immediately subsequent to message 1 to mark t~e end of such message as per blocX 660. A determination is then made at decision block 670 as to whether or not all of the message~ in the group of M messag~s have been retrieved from memory and transmitted~ Thi~ is accomplished by microcomputer 150 making a determination as to whether I ~ presently equal to M. I~ ~icrocomputer 150 finds that I i8 not yet equal to M, th~n I i6 incremented by 1 as per block 680 and flow continues back to retrieve message block 640. The next message, for example message 2, is then retrieved from memory a~ per block 6400 Message 2 is then transmitted as per block 650 and followed by an end of message (EOM) marker as per block 660.
This pxocess conkinues until finally all M Dessages have ~een tran~mitted followed by respective EO~
~arkers. It iB thus seen that the M messages are transmitted as message group.
Fro~ the flow chart of FIG. 5, it will be observed that the group of messages tra~smitted as per block 640 through 680 bear~ a predetermined order relationship with respect to the order o~ the transmi~6ion o~ the addresses o~ the corresponding group of ~ adresses aR per bloc~s 570 through 610.
That is, in this particular example address 1 was ~irst transmitted, ~ollowPd by address 2 and so forth up to address M. In this example, the transmission o~
the group o~ N messages occurs in the same order as the qroup o~ adressQs. That is, message 1 corresponding to the first addres~ is first transmitted ~ollowed by message 2 which corresponds to the second address and so forth up to message M
which corresponds to th~ M'th addressed pager. Other predetermined relationship orders are possible .
' ~

, .

~2~39~

between the order of transmlssion of the messages of the group of M messages and the order o~ the group of M addresses as has be~n discussed earlier. What is important, is that such predetermined relationship between the message order and the address order is known and i~ programmed into the ack-back pagers a i5 di cussed later i~ ~ore detail.
After it i5 determined that the transmission o~
the group of M mes~ages i8 complete as per block 670, }0 flow continue~ to block 690 at which central station 110 pau~es to permit the ack-back pager users which have received messages to key an appropriate response into their ack-back pagers for transmi~sion subsequently back to central station 110. For example, 6uch ack-back pagers may include a keyboard or a switch that is toggled by the message recipient to signify a yes or a no. It will be appreciated that it will take significantly les~ time for a user to to~le one key to indicate a predetermined response, for example a yes or a ~canned mes~age~
(for example, I will call you back), tha~ it would take for a user to key in a respon~e on a keyboard or keypad 6ituated on the pager. ~owever, such keyboard or keypad e~bodiments of the ack-back pager herein 25 are considered to be within the 6cope of the invention in that they provide alternative ways of indicating the user' 5 response to the ack-back pager.
After pausing to permit the addres~ed pager users to key in their responses, centra} station 110 simultaneously receives M ack-back signals ~rom a group o~ M addres~ed pager~ as per block 700. These ack-back respon~es are then provided to the appropriate corresponding callers via telephone inter~ace 140. Flow then continues back to block 510 .
~. .
.

~l2~6~ -to permit other paging message to be input into central station 110.
FIG. 6 is a block diagram of one of ack-back pagers 121,122...P., namely ack-back pager 121. In one embodiment of the invention, ack-back pagers 121, 122...P transmit acknowledge bacX signals on the same radio frequency as th~t on which central ~tation 110 transmits although this is not necessarily a requirement o~ the ~ystem. That is, other embodiment~ of the invention are contemplated wherein the ack-back pagers transmit ack-back signals at frequencies other than within the spectrum of the paging channel employed by central station 110.
However, in the present ~mbodiment, circuitry i~
included within such ack-back pagers to enable the pagers to accurately tune to and transmit ack-back signals within the ~ame paging channel spectrum a~
that employed by central station 110 for tran~mission of paging signal6. ~ore 6pecifically, each of ack back pager6 121, 122... P i6 capable of transmittin~
ack-back signal~ using a plurality o ~ different ~ub~tantially orthogonal pseudorandom codes within the paqing frequency channel on which central station 110 and the acX-back pagerfi transmit and receive.
All of the ack-~ack pagere within a particular group o~ M addressed ack-back pagers ~imultaneously transmit acknowledge back ~ignals back to central station 110 during a time period occurring after such group o~ M ack-back pager~ are addressed and are sent re~pective me~sages. To permit such simultaneous transmi~sion of ack-back ~ignal~ using M different frequency substantially pseudorandom code~ via code division multiplexing (CDMl, it has been ~ound that pagers 121, 122..,P must be able to tune the transmitted ac~nowledge back signal with extremo ~2~39~
2~
~ccuracy in s~requerlcy. The ~ub~eque~tly de~cribed frequency control circuitr3~ within ackob2ck pager 121 permit~ such ~ccur~y ln freauency tuning. An example of one ~ingle c~nver~i3n receiver which is 5 adaptabl~ to acco~od~te the afore:lDentione~ ~requency control cira~ltry gn ~ccord~n~e with t~e pre~ent ~n~ent~on i~ th~ Plotorola Sen~ar ~ri~6 di6play p~ger aE~ de~cribed ~n the publication ~Sensnr~*~erie6 -Di~play GSC Rad~o Pagers, ~Sotorola Public:ation ~o.
68~S1038C75-A.

Ack-~ack pager 121 include~ a tr~ns~nit/receive ~n'cenna ~300 e~bitla~ n l~pprDpriate ~ize a~d ge~Detry t~ permit tr~nsmi~sion ~nd reception a~f lS ra~io freguency ~ignal~ on the rad$o ~reguency pa~ing channel on ~hich ~:entral 6tation 110 tran~mi~6~ ~nd recei~v~6~ antenna 800 i~ coup?ed l:o ~ co~on port ~lOA of a tran~mit xeceive gwit~h 810. Tran6~it/
recelve 6witch ~0 ~n~lude~ A r~ceive por~ hlOE!~ and a tr~nsDIit pc~ lOC in ~ddit~l~n t;c~ ~e ~t~ve ~entioned ant~n~a lnput pc~rt 810A. Bwitch 810 ~nclu~le~ a control irlput ~lOD ~6 ~own in FIG. 6. ~en ~n appropri~te control input e;ign~ 6uppl i~d to control lnput 810E~, tran~mit~receive ~;w~tch 810 ¢oupl~ ~ntenn~ port 13lOA to receive port 810B to place p~ger 121 ln the receitre ~ode. A,lternatively, pager 121 16 p~ced in t.he tran~it ~nod~a when an app;:opr~at~ oc~ntrc~l 6ignal 15 ~upplied tc~ control ~nput 810D ~uch ~at tr~nsm$t reoeive sw~tch 810 coupl~s th~ antl3nna ~nput port 810A to ~r~ns~it port 810C. The~e e:ontrol ~ are ~upplied to oontrol iJlpU~ 810D 3:y ~crt~c:o~p~t~r 820. On~ ~icroproce~sor which ~y be ~Dploy0d ~ ~icrocomput~r ~20 ~ the mcdel MCC:146~705G2 ~anufactur~d ~y ~lotorol2, Inc.
* Trademark ... .

~2~

Receive port 810B of switch 810 is coupled to the input of a radio frequency amplifier 8300 It i~
noted that the frequency of the radio paging channel on which central station 110 transmits i5 defined to be FRX, for example, 150 ~H~. ~hu~, the radio frequency paging ~ignal6 which reach ack-back pager 121 and which are provided to amplifier 830 exhibit~
a frequency of FRX ox 150 MHz. Amplifier 830 amplifie~ th0 radio paying signal~ from central paging station 110 and provides such ampli~ied ~ignals to the input of a bandpass ~ilter 840.
Filter 840 i8 typically of the preselector type which filters off any undesired signal~ adjacent the paging channel frequency.
The output o~ filter 840 is coupled to an input 850A o~ a two input mixer 850. Mixer 850 includes inputs 850A and 850B and an output 850C. A local oscillator 860 which oscillates ~t a frequency of FLD
is coupled via an amplifier 870 tv mix~r input ~50B.
Mixer 850 down-converts the filtered RF paging signal at frequency FRX thereto by mixing such si~nal FLo ~ignal. In thi~ manner, the down converted RF signal generated at th~ output 850C of mixer 850 iB at ~n intermediate frequenay o~ FRX-FLo which i~ de~ined to equal Fc.
Mixer output 850C is coupled to the input of an inter~ediate frequency (IF) amplifier 890 which amplifies the down-converted RF paying signals. The output of IF amplif~er 890 is coupled to a count input 820A o~ microcomputer 820 to determine the down-conver~ed re~erence carrier frequency FC as later described. The output of IF amplifier 890 is also coupl~d to the input a demodulator 900 which demodulates the down-converted RF paging signals provided thereto. That is, demodulator 900 separates - . .

`
, ~Z13~2 the preamble, address, and messaye signals from the carrier wave on which th~y were transmitted by central station 110~ The data signals thus resulting are provided to microcomputer input 820B via a connection to demodulator 900 as shown in FIG. 6.
Such data ~ignal~ include preamble, address, and message ~ignals. Microcomputer 820 of pager 121 decode~ the address signal6 provided at data input 820B and compares the incominy decoded page ~ddresses with the predetermined uni~ue address of such pager 121 which is ~tored in a code memory 910. Code memory 910 is typically an electronically era6able programmable read only memory (EEPROM) ~uch that unique pager address codes are easily assigned and programmed into each of acX-bac~ pagers 121,122... P.
As s~en in FIG. 6, memory 910 is coupled via a buss to a memory port 820C of microcomputer 820. When microcomputer 820 determin2s that one of t~e addres~e6 in ~ received group of M pager addresses corre~ponds to the unique addres6 of ~uch pager 121, then microcomputer 820 decodes the following group of ~ me6sage~. Microcomputer 820 ~elects which of such me~5age~ i6 intended for pager 121.
In a known ~ashion, ~icrocomputer 820 generates appropriate output 6ignals which are ~upplied via linear ~upport ~odule 920 to audio ~odule 930 and ~peaker 940 to alert the pager u~er that a me6sage ha~ been raceived. Th~ 6elected m~C~age is stored in a random access mamory (RAM) 950 which is coupled via a bus to microcomputer memory port 820D. A liquid cryfital displ~y module 960 i~ coupled to the display output 820E of microcomputer 820 ~uch that the selected ~essage received by pager 121 can be displayed for ~iew~ng by the pager user.
Alternatively, the pager u~er can recall ~he page : . :
.

~2~ i2;;:

2~
message from memory 950 subsequent ~o the alert signal for viewing later at a more convenient time.
A clock circuit 970 i8 coupled to a clock input ~20F
of microcomputer 820. Clock 970 provide~
microcomputer 820 with a re~erence time base.
A user reply input device 980 is coupled to a data inpu~ port 820G o~ microcomputer 820 as shown in FIG. 6. In one embodiment of the .invention, the user reply input device 980 i6 a four po~;ition switch, the po~ition~ of whlch are respectively des~gnated as choices A, B, C, and D. By preagreement between the pager user and the pager caller, each of choices A, B, C, an~ D is agreed to have a predetermined meaning. For example, choice A when 6elected by the pager user could be a ~Yes~ response to the caller's me6sage. Choice ~ could be ~No~ response. Choice C
is a nMaybe~ rasponse and Choice D i~ a ~Cannot ~eply Now~ responRe. Th~fis ~killed in the axt readily appreciate that the ~utput of such a four po~ition ~witch when used in input device 980 i6 readily convertsd to a digital 6ignal which i6 ~upplied to data input port 820G for processing by microcomputer 820. Alternatively, a 2 position or YES/N0 switch could be employed ~n user input device 980, It is noted that u~er reply input device 980 is not limited to the multi-position switch which was di~cu6sed above. Rather, other input devices, ~or example, a keyboard or other key entry devices ~ay be employed as user input device 980 in other embodiment~ of the invention to ganerat~ reply data.
The reply data i8 then transmitted back to central 6tatio~ 110 by pager 121 during acknowledge back reply field 390 as 6hown in the a~knowledge back protocol ~hown in FIG. 4E. Each pag~r o~ the group of M ack-back pagers which were addressed now respond .. _ . .. .
`.:

.

.

~L2~

back simultAneously a~ ~ group during t~e appropri~te acknowledge ~ack ~ield. Each of the ~S pager o~ the group respond~ u6ing ~ digferent one of ~
pseudoran~om code~. In one e~nbodiment. o~ the 5 invent~on wherein ~=20" a pseudorandoa~ code o~ length 127 i6 u6ed. Suc~ a cvde ~ generated a~ describe~
~y ;IDhn G. Prl~ak~ in Digit~l Communie2~tions publi~hed ~y ~5cGr~Y Hill ~looX Company, 19~3, ISB~ 0-07 ~50927 1, pages 256-258. In th~ Pro~k~ srr~ngeDent, 10 ~ut:h a cod~ :16 g~nerat~d ~ the output of ~v~n shift r~gi~tero pr~loade~l with the bin~ iqit~ 1000000 ~r~d wh~re r~gi6t~r~ 1 ~nd 7 are combinQd by an eacclusive OR oper~tion ~md god back to the ~ir~t r~gi~ter o~ th~ ~xt clo¢k cycle. ~hu~"~
p6eudo~an~0~ ~equ~nce ~f 127 ~it~ i~ r~p~tedly generateZ. Tho~e ~killed in tlle coding Zlrt6 wil appr0c~ t~ t other ~ubstantially ortllogonal p~eudc~r~ndom ~:~des ~ely be generated and used ~s well e:on~i~tent with pra~ti~e o~ the ~nvent~oJ~. The 20 particul~r ~ how~ ~n FIG. 7 exhi~it6 the property ~at t~ ode ~ t~ntlally t~rthQgc~n~l to the ~me ~:ot!le ~hi~tod by any numb~r o~er t21an a ~ultiple o~
127 ~t~,. In thi~ i~ent og the inventlon, the 127 bit ~:ode ~s a~egmente~ ~nto twenty ~t2rtin~
25 po~t~on6 a~ wn ln FI~;. 7. A r~pect~ve 6t~rting po8ition commenc:~s llt ~v~ry 6ixt:~ bit. Thuf; ~ code nc~ l~ginning w~th blt 1 or ¢ode nu~er 1 in tl:le table o~ ~IG. 7 i~ ortho~on~l to the c~ oqueJ~ce call~d co~ 2 beg~nn~g with S~t m~ r 7 o t}~e 127 30 b$t p~eudo~andt~ od~ eguence ~nd ~o fort~ ontl~ cc~de 20 wh~ch i~ the! ~quenc:~ of 1~7 b~t~ b~ ing w~th blt nun~er 115. gA~ code repQat~ ~ro~ b$1: 1 a~ter l~it 127.

~ . .

2~

More ~pecifically, code l for pager AB-l starts at the designated starting position in the table of FI~. 7, namely 100000 and continues with 011111, 110101 ... 010000. Code 2 for pager AB-2 ~tarts with the designated starting position 01111~ and continues with 110101, 010011 ...110000, and 80 forth for the ~ub~equent codes 3...20.
One of the M pseudorandom code ~equ~ncee is thus under6tood to be the repeating sequsnce o~ 127 bits of Table of FIG. 7 where each of the ~ codes exhibits a unique starting point. The code starting point is designated by the pseudorandom code number (PRC. No.). The pseudorandom code sequence i8 sent at an 8500 bit/ ec rate and i~ modulated by an exclu~ive OR operation with the acknowledge bacX
reply data at a lOO bit/s~c data rate in microcomputer 820. The 8500 bit/sec pseudorandom coded data i6 sent by microcomputer 820 on port 820I
to the data input port 1020B of phase modulator 1020.
A code rate o~ 8500 bit~/sec is suf~icient to 6pread the modulation over approximately .a 15 KHz bandwidth and re~ults in 85 pseudorandom bit~ per data bit which is 6ufficient to render the N codes to be sub~tantially orthogonal to each other.
Each of the group of M pager~ designated AB-l, AB-2 ... AB- 20, and in fact all of the pager~ o~ the population of P acknowledge back pager6 ar~ capable of acknowledging back using any one of the M
di~ferent p~eudorandom codes. That i~, the aontrol progra~ stored within memory 910 is capable o~
directing microcomputer 820 to transmit acknowledge back signals coded by a selected one of the ~ or 20 diffQrent pseudorandom codes.
In more detail, the output of amplifier ~70 is coupled to the input o~ an amplifier 990. Thus, an ',' ' ~ ., ' ~ ' ' 62;~:

amplified replica of the FLo signal from l~cal oscillator 860 appears at th~ output of amplifier 990. The output of amplifier 990 is ~oupled to input lOOOA of a mixer 1000 having inputs lOOOA and lOOOB.
In this manner, the amplifi~d local oscillator ~ignal is provided to mixer input lOOOA. ~he output of amplifier 990 is al~o coupled to th~3 input of a divide by N circuit 1010. Divide ~y N circuit 1010 is a programmable prescaler which digitally divides the FLo signal by an integer value N. Such divicler circuits are well known to those skilled in the art and are readily available from many commercial ~ources. ~h divider circuit selected for dividér circuit 1010 exhibits an allowable range of programmable dividers, N, between 2048 and 8192 and can accommodate an input frequency near 150 MHz for this particular embodiment ~ the invention. Divide by N circuit 1010 ~ co~pled to an input 820~ o~
microcomputer 820 such that ~he ~alue s~lected for N
2 0 i8 provided to divider lO~Oo The frequency of the signal which i~ gen rated at the output of divider circuit 110 i8 equal to FL~/N. The output of divider circuit 1010 i6 coupled to an input 1020A of a two input ~xclusive OR gate 1020. Exclusive OR gate 1020 is employed as a phase modulator and includes inputs 1020A and 1020B. ~he remaining input 1020B of exclu~ive 0~ gate 1020 i~ coupled to the reply data output ~20X of microcomput~r B20. In this manner, reply data which include~ indicia of the acknowledge back respon6e provided by the pag~r u~er a~c user reply input 980 is provided to exclu~ive OR gate 1020 for pha~e modulation onto to F~o/N signal provided at input ~020A. A phase modulated ack-back signal is thus generated at the output of exclusive OR gate 1020.

.. ' .' ~

~2~ 2;~ -The output of exclusive OR gate 1020 is coupled to input 1000B of mixer 1000~ In this manner the phase modulated ack-back ~ignal exhibiting a frequency of FLo/N i~ mixed with the FLo signal such that the ack-back transmit frequency of FTX at th~
output of mixer 1000 i~ equal to FL~ plu6 F~N. The output of mixer 1000 i8 coupled via a ba~dpas~ filter 1030 to a power a~plifier 104C. ~andpass filter 1030 filters any unde~ired signal components from the FTX
signal. A~plifier 1040 amplifies the filtered FTX
Gignal up to a signal level su.~ficient for transmission back to central station 110. The output of amplifier 1040 i~ coupled to the transmit input 810C of transmit/receive switch 810. It is noted that there is a predetermined relationship between the particular pseudorandom code with which each o~
ac:k-back pagers AB-l - AB-20 r ~;ponds to eit~er the order o~ eacA pager's particular addres~; within the qroup of ~ pagers or the order o~ each pager ' ~c 2 0 particular message within the group of M pager~ .
From the earlier discu6~ion, it will be recalled that the order of the message~ within a group o~ ~
messages bear a predetermined relationship ~o the order in which the addresse~; for ~uch messages were 2 5 transmitted in the corresponding address group. The relationship between the selection of pseudorandom code for ack-back transmis6ion and the order of transmission o~ the M addresses or M messages is e~tabli~hed to enabl~ microcomputer 150 in ~entral sta~ion 110 to determine which ack-back ~ignal code transmission corrasponds to whic~ acknowled~e back pager addres~ of the group o~ M pager~.
For example, a~suming th~t pager AB-1 in the p~eudorandom code look-up table of FIG. 7 i6 the 3S fir~t aak-back pager of the group of M pagers to be ._ _, ~ ,.. _.. . . , . . ~ ~ . . ., ........... ... .. , .. ._ . . . , . . .. . _ ,~''` '.' . ' ~ ~ .

~2139~;;2;~

addressed or recei~e a message, then, ack~back pager AB-1 responds back on a with a pseudorandom code designated pseudorandom codes 1 (or PRC No. 1) which corresponds to the code ~tarting point noted in Table 1. Assuming that pager AB-2 in the table of FIG. 7 is the second pager o~ the group of M pager6 ~hich is addressed or sent a message, then, pager AB-2 acknowledges back with the code 6tarting at pseudorandom code positions as shown in the t~ble of FIG. 7. To continue this example, a~suming t~at pager AB-20 i~ the twent~eth pager o~ the group of pagers to be addressed or receive ~ message, then pager AB-20 acknowledges back with th~ code starting at position 20 (PRC No. 20~ a~ ~hown in FIG. 7.
15 Although each of pagers AB-~, AB-2 AB-20 responds back with a different respective pseudorandom code 1 20 noted in FIG. 7, all of 6uch pagers respond back simultaneously at the ~ame ~requency in a common time slot or field a~ already described.
It i~ noted that o~her predetermined relation~hips betwaen the ack-back code order and the order in which the addres~es or me~sages were transmitted to the group of ~ pager~ may be employed.
That i6, although in the example above, the order of the ~ addresses (or M ~essages) and the corresponding order o~ the M codes are both ascending, in another embodim~nt o~ the invention in which the order of the addres&es of the group o~ M pager~ AB-1 ... AB-20 is the ~ame as the prior example ~a~cending), the order of the acknowledge back codes i~ rever6ed a~ compared to the prior examplQ ~descending). That is, pager AB-l responds back w~th code 20; pager AB-2 re~ponds back on code 19 ... and pager AB-20 respond back on code 1.

' ~ ' . . , . . . ' .
' ~;~8~6~2 Al~o, as mentioned briefly earlier in this document, alternatively in another embodiment of the invention, the relationship between the order in which pager addresses or messaqes were received by the group of M pager~ and the order of assignment of pseudorandom codes ~or ack-back to ~uch ~ pagers can be arbitrary. What is important is that a predetermined relationship exi6ts b~etween the order o~ as6ignment o~ codes and the orde:r in which the pager addresses or messagee arrive at the group of pagers. Again, thi~ predetermined relationship is programmed into memory 170 of microcomputer 150 in central station 110 such that microcomputer 150 can determine which code i~ being u~ed by each of the pager~ AB-l, AB-2 ... AB-20 as they acknowledge back.
An example is now presented showing how one of the AB-l, AB-2 ... AB-20 pager~ selects a pseudorandom code on which to respond and generates an ac~nowledge back ~ignal using that code. For purposes of thi6 example, the third pager to be addres~ed or receive a mes~age in the group of N
pager~, that i~ pager AB 3, will be discussed. In thi6 exa~ple, unlike the example of FIG. 4H, pager AB-3 i~ an acknowl~dge back p~ger. After reading the me~sage which i~ supplied to the di6play 960 of pager AB-3 ~such as pager 121 of ~IG. 6), the pager AB-3 u~er indicakes a reply at input device 980 ~8 already di~cussQd. ~he control program in memory 910 of pager AB-3 causes microcompuker 820 therein to recognize that AB-3 i~ the third pager o~ the group M
= 20 pagers to be addre~sed. A pseudorando~ code and code look-up table is ~tored in memory 910. The code look up table includes the appropriate ~tarting point for each of the 20 di~ferent pseudorandom codes as shown in FIG. 7. As mentioned, microcomputer 820 of .

.

: .
' 362~ -pagPr AB-3 determines that it has received the third address or third message in the respective address or messa~e yroup sequences. Using thi6 in~ormation, microcomputer 820 f~tches from memory the particular S code fr~m the code look up tahl~ in ~emory 910 which correspo~dc to the third code or code 3.
In the circuit arrange~ent o~ FIG. 6, the ack-back frequenay FrX equal~ FLo plu~ FL0/N- FL0/N
varies with the amounte of error betw@en the FLo local oscillator frequency and the FRX reference frequency. It i8 noted that the FRX paging channel center frequency is ~tored as a referenae number in memory 910. In the above equation de~ining FTX~ N
equals (F~X ~ FC~/Fc. Microcomputer 820 performs the calculation of N and provide~ the value of N to divider circuit 1010. More specifically, to calculate the value of N, microcomputer 820 determine~ the frequency of the down-converted reference carrier ignal, Fc~ by counting the ~requency of such signal at microcomputer input 820A
during reference carrier trans~ission time T3.
~icroco~puter 820 retrieves the FRX reference center frequency value from memory 910. With all the variable~ which define the dIvisor N thus being known, microcomputer 820 calculates th~ value of N
and supplie~ the ~ame to divider circuit 1010 as already described. The signal gener~teA at the output of divider circuit 1010 thu~ exhibits a frequency of FLo/N. The FLo/N ~ignal is mixed with the FLo signal at mixer lOQ0 to generate the F~X
transmit ~requenay o~ FLo + FLO/Nr It i6 appreciated that by replacing N with the expre~sion for N, we get FT~ = FLo+FLo/N ~ F~o+F~o(Fc)~(FRx-Fc)~ By defi~ikion FLo = FRX-FC si~ce both Fc and FLo contain exactly the opposite freguency error. It follows . , .

3t6%~:

that the sum F~o+F~ ca~cels the frequency error. It is noted that FTX = FLo+FC = FRX exactly.
The present circuit arrangement uses the local 06cillator frequency FLo as a reference for s generation of the ack-back transmit frequency F~x.
It i~ noted that the circuit arrangement described above, corrects for dif~erence~ in the freq~ency of the local oscillator FL~o Although, a single conversion embodiment of acknowledge back pager 121 is shown in FIG. 6 and described above, tho6e skilled in the art will appreciate that double and other multiple conversion embodiments of the pager are readily adapted from this invention an~ are intended to b~ within its scope.
Each of pagers 121,122...P includes a threshold detector 1050 coupled between the output of amplifier 890 and input 820J of ~icrocomputer 820~ Threshold detector 1050 provide~ input 820J a logical 0 when the down-conver~ed carrier ~ignal at FC exhibit6 a voltage level less than a predetermined threshold level. However, when the signal voltage level of the FC carrier ~ignal i~ equal to or greater than such selected predetermined voltage level, then thresh~ld detector 1050 provides a logical 1 to microcomputer input 820J. T~e threshold is set, ~or example, 80 that a ~ignal at the receiver input which is 40 dB
above minimum usable recsiver sensitivity will trigger threshold detector 1050. ~icrocomputer 820 includes a power control output 820R which i6 coupled to a power level control input ~040A of variable output power amplifi~r 1040. Amplifier 1040 is of the ~ype which can a~ume different power output levels depending upon the value of the ~ignal provided to 1040A. For example, in this particular , , ,, `

embodiment, when a logical 0 i8 provided to input 1040A, amplifier 1040 operates or transmit~ at ~ull power, for example at approximately 1.5 watts output.
Howe~er, when a logical 1 i~ provided to input 1040A, amplifier 1040 throttles back or reduces power to a second lower power output level which is approximately 40 dB le68 than the ~ull power output level. In summary, in this embodiment of the invention, when a logical 0 i8 provided by threshold detector 1050 to microcomputer input 820J indicating that a relatively lvw level Eignal iB being received, then microcomputer 820 generates a logical 0 at its output 820K. This cause~ amplifier 1040 to amplify at the fir~t or full output power. However, when threshold detector 1050 provide a logical 1 to micr~computer input 820J, indicating that a relatively high level signal i~ ~eing received, microcomputer 820 then generate a logical 1 at output B20K. ~his in turn causes ampli~ier 1040 to throttle back to the 6econd lower output power level.
The above de~cribed variable output power level circuit arrangement aids in avoiding the situation when any one of the group of M pagers AB~ AB-20 generates ~uch a 6trong ack-back signal at central ~tation 110 that such signal exceeds the dyna~ic range of the receiver of sta~ion 110 and ma~ks the ack-back signals from the other pagers of the group o~ M.
Although in this particular embodiment of the invent~o~, a two power level amplifier 1040 is employed in conjunction with a single level threshold detector 1050, the invention m~y al~o be practiced using thre6hold detectors with more than one threshold and variable output power amplifiers with more than two selectable output powers. For example, .
:, , .

in an alternative embodiment of the invention, threshold detector 1050 is a three range threshold detector which determines if the Fc signal exhibits a low, mediu~ or high signal level. Such a threshold detector conveniently employ6 first and second thresholds. That i~, when threshold detector 1050 determines that the received signal level at the pager is within a fir~t predetermined low signal level range (less than tha ~irst threshold), then microcomputer 820 causes a three output power level amplifier, employed as ampli f ier 1040, to ampli~y at a high output fir~t power level. When the thre~
range detector 1050 detect~ that the received ~ignal lev~l is within a ~edium signal level range (between the ~irst and ~econd thresholds), then ~icrocomputer 820 would causes amplifier 1040 to amplify at a medium output second power level. When detector 1050 determinec that the recei~ed ~ignaI level i~ within a third high level range (above the ~ec~nd threshold level), then microcomputer 820 c~u~es amplifier 1040 to fully throttle back ~o a th~rd and lowe~t power output level~ Thu6~ a power control circuit i5 provided in which the transmitted output power of the ack-back pager varie~ inver6ely with the RF signal level of the paging signals it receives from central station 110.
~icrocomputer 820 i~ programmed to generate a logical 1 at port 820L during the period of time at whlch pager 121 is to transmit an acknowledge back signal back to central ~tation ~10, for examp~e, ack-back time period 390 as ~hown in FIG. 4E. During all other periods of time for which pager 121 should be in the receive mode, ~icrocomputer 820 iB programmed to generate a logi~al 0 at port 820L. When a logical 1 i8 generated at output 820L, indicating transmit .

._ . . ... . .. , , ", . .. , ~ .. .. .

~89~i~2 mode, transmit/receive switch 810 connects antenna port 810A to por~ 810C thus connecting the transmit amplifier 1040 to antenna 800. However, when a logical 0 i8 provided to microcomputer port 820~, transmit/receive switch 810 couples antenna port 810A
to port 810B and receiver amplifier 830.
FIG. 8 i~ a flow chart of the control pro~ram ~tored in memory 910 which control8 the operation of microcOmpUtQr 820 and pager 121. A power-on-reset step i~ ~hown ~n block 1100. Program variable~ are initialized at this time. The receiver portion of pager 12 1 is turned on and becomes ~ynchronized with resp~ct to the paging signals trans~itted on *he paging channel by central station 110. After becoming initially synchronized, pager 121 goe~ .into a ~leep ~ode~ or battery saving mode as described earlier. When pag~r 121 receiv~s a preamble signal, a~ in block 1110, pager 121 wakes up a~ per block 1120. An address.count variable, ADRCOUNT, i6 then initialized with ~ value of 0 as per block 1130. A
variable ADRMAX which repr~sent6 the maximum number of ack-back pagers in an ack-back group is set to have a v~lue of M as per block 1130. Pager 121 listen6 to each of the addresses within a group of M
addre~se~ to detexmine if its particular address is received as per block 1140. For exampIe, at block 1140, the ~irst address of a group of M addresses.is checked to determine i~ it is t~e valid address ~or the particular pager 121. If the first addres5 i5 not the addrese of pager 121, then the ADRCOUNT
variable ~s incremented by 1 to count the number of pager addresses already rec~ived as per block 1150.
A determinati4n is then made as to whether all of the addresses of the group of M addresses have been proces ed, block 1160. If the variable ADRCOUNT is .
- . , . . '. :

~2~39622 equal to M, then the address of the particular pager 121 has not been received and such pager 121 reenters the battery saver mode as per block 1170 after which pager 121 again powers down and looks to determine if a preamble ~ignal i8 received. If however in block 1160 ADRCOUNT is not egual to M, that i5 le~s than M
signifying t~at all of the M addrese;es of a group of M addresses have not been received a~ in the present example with respect to the fir~t acldrass of such group, then ~low continues back to block 1140 where pager 121 checks the next address in the group of M
addresses for validity. If any address within the group of ~ addresses i6 determined to be the address for the particular pager 121, then flow continues from block 1140 to block 1180 at which the variable - ADRCOUNT i~ incremented ~y 1 ~uch that ADRCOUNT is a number which repr2~ents the order of the valid address wi~hin the sequencing or group of M
addresses.
APter tha group of M addressee i6 received by pager 121, pager 121 receives and determines the frequency of the down-converted reference carriex FC
as per block 1190, The ~ignal ~trength of the carrier FC i8 then ~etermined by micro processor 420 a~ per block 1~00.
In the following ~teps, the particular message withi~ the group of ~ me66ages which i6 intended for a particular pager within the group o~ M addressed p~gerB iB matched with such pager and displayed thereon. More particularly, prior to commencing to count the ~umber o~ messages within the group of M
messages as such me6sages are received, a me~sage count variable ~SGCOUNT i~ initialized at a value of 0 as per block 1210. The receiving o~ the individual mes6ages of the group of M mes6age6 commencas as per block 1220 at which the next message of such group is received. Initially, the first message of the group of M ~es~ages is the ~next message~ received. Upon reception of a message, the MSGCOUNT variable is incremented by 1 to count the number o~ message6 that have been received as per block 1230. A
determination is then made as to whlether MSGCOUNT
equal6 ADRCOUNT at block 1240. I~ it i8 determined that MSGCOUNT doe~ ~ot equal ADRCO~NT, then ~ore messages remain to be rQceivsd in the group of ~
messages and ~low continues back to block 1220, at which the next message is received. In this exa~ple, wherein the Pirst message was received the ~irst time around the loop formed between block 1220 and 1240, the second message is received the second time around such loop and the message counter MSGCOUNT is incre~ented at 1230 accordingly. ~hen a det~rmination i5 ~ade that MSGCOUN~ equals ADRCOUNT
then, the curxent ~e sage is di~played at bloGk 1250.
In ~his manner, the particular ~essage which was intended for ~ pager within the group of M pager~ is displayed by matchinq the order of the occurrence of such ~e66~ge in the group of ~ me~sages with respect to the order of ~he corresponding address within the group of M addre~se~.
Ack-back data i8 supplied to microcomputer 820 by the pager u~er as per block 1260. The ack-bAc~
pager waits s per block 1270 for an ack-back field (time interval) be~ore responding back to the central 3tation lO0 with the ack-back data provided by the pager user. It was di~cu~6ed earlier that ~
different pseudor~nd~m code~ are available in the pager of the invention for transmis~ion o~ ack-back Gignal~. Each ack back pager within a group o~ M
addres~ed p~ger~ responds back to the central ~tation ~, : - ', , . , ~ .
.
', ' ; '' ~ .
. .
.

~l21~9~i22 110 on a different respective pseudorandom code based on the value of the ADRCOUNT variable determined above for such pager as per block 1280.
For example, in one embodiment of the invention, if a particular pager wit~in the group of M pager~ is the fifth pager of the group to be addre~sed, then such pager has an ADRCOUNT value o~ 5. A~ per the above discu6~ion, the fifth message in the group of M
message~ corresponds to the ~ifth pager addressed and 0 i8 appropriately provided to the di~play of ~uch fi~th pager ~or viewing by the pager user. ~n this particular pager wherein ADRCOUNT equals 5, code number 5 i~ ~elected from the table of FIG. 7 for use by such pager for transmitting it~ ack-back ~ignal.
That is, the value of ADRCOUNT determines the particular pseudorando~ code which is selected for ack-back. Since in thi~ particular example code 5 iæ
~elected, ~icr~comput~r 820 accesse~ the code ehart of the table of FIG. 7 and looks up the pseudorandom code ~tarting point corresponding to code number 5 as per blo~k 1290. ~icrocomputer 820 then looks up the value of the pager channel center frequency FRX in memory as per block 1300. ~he value o~ Fc, the down-converted carrier freguency, ~ then retrieved from ~emory or i~ otherwi6e acguired as per block 1310.
Using the retrieved values o~ FRX and Fc, the value oP the divisor N i8 determined according to the equation N = (FRX ~ FC)/(F~ as per block 1320.
Divider 1110 in FIB. 5 i~ then ~et to have ~ N value a~ determined above in order to drive the freguency of the ack-baak paqer to exactly 150 MHZ as Bet in block 1330. In this example, F~X ~ 150 MHz, FC =
O.0350 MHz, znd the neare~t integer value for N i~
N = 4285. The resulting ack ~ack transmit frequ~ncy FT~ i~ therefore 14g.9999977 M~z which i~ 2.3 Hz from ~;~89 Ei;22 the desired transmitter frequency and well within the 30 Hz freguency tolerance required in this particular embodiment of the invention.
A determination is then ~ade by micrscomputer 820 as to whether the ~ignal level of the Fc reference carrier i6 greater than th~ aforementioned predetermined threshold level. If the Fc ~ignal level is greater than a predetermined threshold level as determined at block 1340, then the transmitter 1~ circuits of pager 121 are turned on, a~ at block 1350. The ack back data i8 then tran6mitted back to central station 110 at a low power level using the already ~elected code via code division multiplexing as per block 1360. After transmission of the ~ck-back data, the transmitter circuits are turned ~f atblock 1370 and the battery ~aver mode i8 reentered as at block 1170. If, however, it i~ determined at block 1340 that the Fc carrier re~erence si~nal does not exhibit a signal level greater than the predetermined thre~hold, then the transmitter circui~s of pag~r 121 are turned on at block 1390 and the ack-back data i6 transmitted back to central station 110 at a high power level using the 6elected pseudorando~ code via code division multiplexing as per block 14~0. After 6uch transmis~ion of the ack~
back data, the transmitter circuits are turned off at block 1370 and the battery saver mode i8 reentered at block 1170.
From the above de~cription, it is clear that the invention involves ~ method o~ radio paging which is employed in a radio paging ~ystem including a paging terminal or central ~tati~n for transmitting address and me~sage ~ignals to a plurality o~ remotely located radio pager6. Each o~ suc~ pagers has an addre~s corresponding thereto. The method of radio _ __ _ _ . . _ __ . , .. _ .. ... ... .. . . . ... ., .. _ .. ... . _ .. _ _ _ ._ ._ .. ,. .. _ _ , _ ... . .
.

:. ~ ` ,, ' ' ' : ' .
.

paging includes the step of sequentially transmitting a batch of M pager addresses during a first time period, wherein M is the number of pager addresses in said batch. The method further inoludes the step of the batch of pagers addressed in the aboYe s~ep transmitting respective acknowledge back signal~
simultaneously in a ~econd time period ~ubsequent to said ~irst time period, each of ~uch batch of pager~
transmitting a different ~ubstantially orthogonal pseudorandom code which is assigned to each respective pager.
In 6u~mary, the foregoing describes an apparatus and ~ethod for radio paging which permits the pager user to respond to the pager caller. Each radio pa~er is capable of responding back to the paging terminal and the caller. Moreover, a group of M
addre~ed ack-back pager~ are capable of simultaneous~y tran~mitting acknowledge back signals on a ~elected fre~uency, each pager transmitting a respective acknowledge back signal using a different 6ubstantially orthogonal p~eudorandom code.
Nhile only certain preferred feature~ of the inYention have been fihown by way of illustration, many ~odi~ication~ and changes will occur to those skilled in the art. It is, therefore, to be under~tood that the present claims are intended to cover all such modi~ications and changes which ~all within the true spirit of the invention.

, .
' ' ` ' '

Claims (20)

46 We claim:

1. An acknowledge back pager having a unique address associated therewith, said pager comprising;
receiving means for receiving paging signal from a central station, said paging signals including a batch of M pager addresses transmitted in a sequential order during a first time, period, wherein M is the number of pager addresses in said batch;
decoding means, coupled to said receiving means, for detecting the presence of said pager's address within said batch of M addresses;
address order determining means, coupled to said decoding means, for determining the order of said pager's address within said batch of M addresses, and pseudorandom code transmitting means for transmitting an acknowledge back signal at a selected frequency, said acknowledge back signal including a selected one of a plurality of M substantially orthogonal pseudorandom codes, said selected one of said codes exhibiting a predetermined relationship to the order of the address of said pager within said batch of M addresses.

2. The acknowledge back pager of claim 1 wherein said batch of addresses are designated 1, 2, ... M
based on the order in which the addresses of said batch of addresses are transmitted and wherein said plurality of pseudorandom codes are designated 1, 2, ... M, said pseudorandom code transmitting means assigning itself a respective pseudorandom code based on the same order as that in which the address corresponding to such pager was transmitted by said central station.

3. The acknowledge back pager of claim 1 wherein said batch of addresses are designated 1, 2, ... M
based on the order in which the addresses of said batch of addresses are transmitted and wherein said plurality of pseudorandom codes are designated 1, 2, ... M, said pseudorandom code transmitting means assigning itself a respective pseudorandom code based on the reverse of the order as that in which the address corresponding to such pager was transmitted by said central station.

4. The acknowledge back pager of claim 1 including alert means for providing an alert to indicate to a user of an addressed one of said M pagers that said pager has been addressed.

5. The acknowledge back pager of claim 1 including a response indicating means wherein a user of said pager indicates a response to said pager for transmission in said acknowledge back signal.

6. The acknowledge back pager of claim 1 including memory means for storing a look up table of said M
pseudorandom codes.

7. The acknowledge back pager of claim 1 including means for receiving and displaying message signals transmitted by said central station in a second time period subsequent time period.

8. An acknowledge back pager having a unique address associated therewith, said pager comprising;
receiving means for receiving paging signals from a central station, said paging signals including a batch of M pager addresses transmitted in a sequential order during a first time period, wherein M is the number of pager addresses in said batch;
memory means for storing a look-up table of M
pseudorandom codes including pseudorandom code 1, pseudorandom code 2, ...pseudorandom code M;
transmitting means for transmitting acknowledge back signals at a selected frequency employing a selected one of said M pseudorandom codes;
microcomputer means, coupled to said receiving means and said memory means, for processing paging signals received by said pager, said microcomputer means including decoding means for detecting the presence of said pager's address within said batch of M
addresses;
address order determining means for determining the order of said pager's address within said batch of M addresses, and pseudorandom code control means, coupled to said transmitting means, for generating an acknowledge back signal coded with a selected one of said plurality of M predetermined pseudorandom codes, said selected one of said pseudorandom codes exhibiting a predetermined relationship to the order of the address of said pager within said batch of M addresses.

9. The acknowledge back pager of claim 8 wherein said batch of addresses are designated 1, 2, ... M
based on the order in which the addresses of said batch of addresses are transmitted and wherein said plurality of pseudorandom codes are designated 1, 2, ... M, said pseudorandom code transmitting means assigning itself a respective pseudorandom code based on the same order as that in which the address corresponding to such pager was transmitted by said central station.

The acknowledge back pager of claim 8 wherein said batch of addresses are designated 1, 2, ... M
based on the order in which the addresses of said batch of addresses are transmitted and wherein said plurality of pseudorandom codes are designated 1, 2, ... M, said pseudorandom code transmitting means assigning itself a respective pseudorandom code based of the reverse of the order at that in which the address corresponding to such pager was transmitted by said central station.

11. The acknowledge back pager of claim 8 including alert means for providing an alert to indicate to a user of an addressed one of said M pagers that said paper has been addressed.

12. The acknowledge back pager of claim 8 including a response indicating means wherein a user of said pager indicates a response to said pager for transmission in said acknowledge back signal.

13. The acknowledge back pager of claim 8 including means for receiving and displaying message signals transmitted by said central station in a second time period subsequent to said first time period.

14. The acknowledge back pager of claim 8 wherein said pseudorandom code control means includes fetching means for fetching from the look-up table stored in said memory indicia of the selected pseudorandom code which said pager is to transmit.

15. In a radio paging system including a central paging terminal for transmitting address and message signals to a plurality of remotely located radio pagers, each pager having an address corresponding thereto, a method of radio paging comprising the steps of:
A. sequentially transmitting a batch of M pager addresses during a first time period, wherein M is the number of pager addresses in said batch;
B. the batch of pagers addressed in step A
transmitting respective acknowledge back signals simultaneously in a second time period subsequent to said first time period, each of said batch of pagers transmitting a different pseudorandom code which is assigned to each respective pager.

16. The method of claim 15 including the step of assigning M different pseudorandom codes in a predetermined order to respective pagers within the batch of M addressed pagers, said predetermined order of such assignment exhibiting a predetermined relationship to the order in which said batch of M
addresses were transmitted by said central station.

17. The method of claim 15 including the step of assigning N different pseudorandom codes in a predetermined order to respective pagers within the batch of M addressed pagers, said predetermined order of such assignment exhibiting the same order as the order in which said central paging terminal transmits the addresses of said batch of M addresses.

18. The method of claim 15 including the step of assigning M different pseudorandom codes in a predetermined order to respective pagers within the batch of M addressed pagers, said predetermined order of such assignment exhibiting the reverse of the order in which said central paging terminal transmits the addresses of said batch of M addresses.

19. The method of claim 15 wherein said paging terminal transmits on a predetermined radio channel having a spectrum associated therewith and wherein said batch of M pagers transmit acknowledge back signals to the central terminal such that all of the respective pseudorandom codes with which such batch of N pagers transmit are within the spectrum of said channel.

20. In a radio paging system including a central paging terminal for transmitting address and message signals to a plurality of remotely located radio pagers, each pager having an address corresponding thereto, a method of radio paging comprising the steps of:
A. sequentially transmitting a batch of M pager addresses during a first time period, wherein M is the number of pager addresses in said batch;
B. providing an alert to indicate to a user of an addressed one of said M pagers that said pager has been addressed;
C. indicating respective responses to said M
addressed pagers;
D. the batch of pagers addressed in step A
transmitting respective acknowledge back signals indicative of the respective responses provided thereto, such acknowledge back signals being transmitted simultaneously in a second time period subsequent to said first time period, each of said batch of pagers transmitting acknowledge back signals with a different one of M pseudorandom codes which is assigned to each respective pager.