CA2098578C - Antenna pattern selection for optimized communications and avoidance of people - Google Patents

Abstract

An antenna selection technique is used in an RF communication system in which user modules (UM1-UM5) communicate with at least one node (N1-N2). The UM's (UM1-UM5) and nodes (N1,N2) each have multiple antennae. The combination of each UM and node antenna is evaluated at the UM. Based on at least signal quality, the UM (UM1-UM5) selects its antenna and the best node antenna for use. An alternate antenna is selected if a person is determined to be present in a predetermined area adjacent a UM (UM1-UM5) corresponding to a predetermined RF power level.

Description

WO 92/13398 PCI`/US91/~1769~
~ 1 . ~G9~578 ANTENNA PATTERN SELECTION FOR OPTlMeED
COMUUNICATIONS AND AVOIDANCE OF PEOPLE
Background o~ the Invention This invention generally add~v- ,ses a ~ ~ ' E system in which a plurality ot spatially separated devices uUlke RF
rorn~ s arld more ~ .l, v~es a method tor selecting the best antenna pattem trom among several choices o~ antenna pattems. This invention is especially surted tor, but not limited to, an g.,.:.~."".~"t in which multipath si~nals and tadin~ problems are si~nificant such as in an RF communication system located inside a buildin~. n also a~J~v~_ antenna selection techniques which take the presence ot people into axount.
n is ~enerally known that directive antenna patterns can be utilized to enhance RF ~ ~' ' between remote RF: ~ It is also ~enerally known that various means exist tor ~ `r~ an antenna radiation pattem such as by rotatin~ a high~y di~vuti~ldl antenna, ~-~.."' ,~ the phasin~ ot different antenna elements to ~' 'r~ ,' 'Iy 25 steer the primary beam or radiation pattem, and the selection of different u;.. " ~al antennas tar~eted at different locations.
Methods tor selectin~ an optimal antenna pattem vary greatly dv~Jvl.di,.~ upon the L.l~i.ulllllvllL In ,..;~,... - line ot si~ht communication ~,, " , the antenna pattem selecUon is simple: just 30 orient hi~hly ~ " . ' antennas poinUn~ at each other. Physically 3~ antennas may be utilized by an RF i ' ~. to enhance communications that are not line of si~ht. In such diversity f ~ s vach antenna may bf3 monitored with th~ ~ntenna havin~ the optim tl wo 92/13398 PCI /US91 /0769~

-2- 2~98578 ~
si~nal being select~cl for use or all of the antennas may be combinec1 utilizing the proper phasing to ~enerate an enhanced single signal.
A number of factors make the problem of antenna pattem selection dimcuit. The reception of multipath si~nals, i.e. receivirl~ the same signal at differerlt ffmes with d~fferent signal stren9ths Irom different 9GC~
locations, greatly c , ' ~ antenna pattem ~ebcffon. The constant tading ot si~nais aiso adds to the problem. These factors are present inside a buildin~ in whicn RF t~ ~mm~ usin~ the 1-100 GHz (~;~al.c.k) frequency ran~. The relaffvely ciose distances between the antennae and re~lectors, such as wails, tioors, ceilin~s and other metal objects large relaffve to the ~ th, resu~t in strong muiffpath signals. Cc ' m~ tading resuKs trom .~
chan~es wch as the ". . ~ Il ot people or objects. K is ~enerally desirable to minimize a person's exposure to RF radiaffon. There exists a need tor an antenna pattem selection method which optimizes 07m~-l ' ~ in such an ~ ,.:r~, S~IMMARY QF THF ~NVFNTIQN = ~
In accordance with the present invention, there is provided a radio frequency (RF) remote module lRM) capable of RF communication with a communications system. The RM selects an RM antenna pattern from a plurality of directional antenna patterns that cover different geographic areas relative to the RM; and periodically generates a signal quality -ranking for a plurality of remote device antenna patterns for the RM
based on signals communicated between the RM and the communications system. The RM antenna pattern is selected to have the best quality rank for communications between the RM and the communications system. A person's exposure to RF radiation from said RM is limited when the person is within a predetermined area adjacent said RM.

Wo 9Ztl339X PCr~lS91/076gc ~2~a~- 2098578 Brie~ D ~ of the Drawin~s FIG. 1 is a dia~rsm of an RF ~ ~ . system employin~ an 6.11hu~1i "~ of the present ~nvention.
FIG. 2 is 8 block dis~ram which shows sn ~
of an RF `~ .. with antenna selection in aocord with the present invention.
FIG. 3 is a tahle illustrating differer~ antenna pe~ r ..a,~
messur~ments made in ~ ' 1ce with an ~"l ,Ji - ~ o~ the present 1 0 invention.
FIG. 4 is a flow dia~rsm illustratin~ an ~ of a method in do~rJdllc~ with the present invention for ~ the initial pe"c"",dnce measurements used in the table shown in FIG. 3.
FIG. 5 is a flow diagrsm in ~ . with sn ~ of the 15 present invention for selectint~ the hest pel~"";"~ antenna st a node.

;

WO 92/13398 PCr/US91~07695 209~ ~8 FIG. 6 is a flow dia~ram in awurJd,lce with an ~"IL,uJ;",~rlt of the present invention illustratin~ a method tor continuously updatin~ and selectin~ the best antenna for use at a user module.
FIG. 7 is a flow dia~ram in ac~rJal ce with an ~"IL~Ji",a,lt of the 5 present invention illustrating a method for continuously ~ 9 and selecting the best antenna for use at a node.
Description of a Preferred [illL~ " ~ It FIG. 1 shows an illustrative RF communications system havin~
nodes N1 and N2, and user modules UM1-UI\15. The nodes and user modules each include an RF l,dnsc~iv~r enabling each user module (or remote device) to communicate with the nodes. The outside wall of one floor of a building is ~ ,s~ ad by dashed line 10. Interior walls 12 15 divide the space into diflerent areas. In the illustrated example, interior walls 12 do not pass RF energy and in practic~ may constitute moveable metal walls in an oflice ~ .U~ lt.
Node N1 communicates with user modules UM1-UM3. Node N2 communicates the user modules UM3-UM5. Thus, user module UM3 20 I~Jrt,St,,..~. a common cell capable of communicatin~ with either node.
Node N1 can also communicate directly with Node N2 by wire communication channel 14. Thus, each of the user modules can communicate wlth any of the oth~r user modules in this system. It should be noted that a user module such as UM1 may not have a line of sight 25 path to any node and thus must utilize a communications path including at least one reflection. U will be apparent to those skilled in the art that UM's with a line of sight communication path to a node will also receive multiple reflected si~nals.
Module UM3 can communicate with node N1 by direct path 11 or path 13 which includes one reflection off of wall 10. ~.. r".: "',s 11A
and 13A extend from module UM3 about paths 11 and 13, .~ ,~ 'iv~l,l, and represent areas in which the power of si~nals lld,,~,,,;l~ad from UM3 using these paths are at or above a p,. '~: -,.,;"ed ",a~" ~da It is desired that people avoid prolonged exposure to radiation at su~h WO 92~3398 PCl/US91/07695 2~8~8 ,4 ",a~ dec Assume that the person shown in Fig. 1 be~ins to wslk from position 15A to position 15B, and that UM3 is lldl)OI "" IS,~ over path 11.
UM3 will ôwitch to path 13 ôhOrtly atter the person enters area 11 A and will continue to use that path as the person au~,ud~ s srea 13A.
Shortb atter the perOon enterO area 1 3A UM3 will ôwitch back to using path 11 and will continue to use ~7ath 11 until a person enterO area 11A
or the ~, G F ~ 1 dt,l~riu, ' ~ such that another path provides a better communications path. The means uOed by the user module tor avoiding prolonged radiation on paths where people are in the p. ' ~ 7d areas will be explained below.
FIG. 2 ~llustrateO an ~. . "f~la, y ~r"L cn~;" ,~"t ot an RF transceiver 16, an antenna selector 18 and a plurality ot selectable directive sntennas A1-A6 which maybe used as part of either a node or user module. In this illustrative 6"~l~Ji"~ six 1. 1l' " . -:7al antennae with 60 degree beam widths are located in a generally horizontai pbne to ~ive 360 degree pattem coverage. A data input/output channel 20 may be coupled to one or more data devices. In the case ot a uOer module, channel 20 could be coupled to a personal computer, an Ethemet port, or a digitized voice source. If utilized as a node, the data input/output channel 20 may consist of a wireline data comn~ 5 link 14 with other nodes and may also be coupled to other data devices. The t,- ,~s~,e;/~, 16 contains a c~"~ al receiver tor receiving RF sigrlals including apprvp~ 7 and decl'sion making circuitry tor decoding received signals into c~llua,uullJill~ data. The ~ 5ce;J~ir also contdins an RF tld,7;"~,ittt7r with suitable modulation and encodin~
circuitry to encode data to be l,d,, ,,~,a~d overthe RF canier. The RF
signals tldll;,lll'~ ~ and received by receiver 16 are coupled to antsnna selector 18 by cable or waveguide 22.
The antenna selector 18 is capable ot selecting any one of the six antennas A1 -A6 for use by lldl~aC~, . er 16. In order to rapidly select one o~ the available antennas, electronic switchin~ is preferably utilized to select the desired antenna. Of course, c~"fu.,tivl7al ",6.,1,a";~,dl switching can be utilized if suitable for the particular ~ . The antenna s-lector contains a .,.;~,,u~ru"~ssor and ~csu.~; ~t~d support wo 92/13398 PCr/US91107695 2~9~`~78 drcuitry for ' ~~I~ lin~ which antenna should be utilized as will be explained in detall below. At ",iu,.,.._.~ frequencies, the antennae may constitute hom antennae or other directive antennae and are preferably arran~ed to provide complete 380 de~ree covera~e in a horizontal plane 5 with app.u~,~ vertical beam widths to provide latitude for the reception of si~nals from virtually any location relative to the node or user module.
It will be apparent to those skllled in the art that the antenna selector 18 may be physically housed within transceiver 16 if desired.
In the illustrated ~,,l~d;,ll~,lt of the present invention, 10 communications between the nodes and user rnodules is aco~"",l;sl\ed usin~ a time division multiple access system in which packets of data are lldll~lll;t~ ~. The nodes send packets ~ ;nS~ an address and other related overhead i,.~ ",~ ~ ~ alon~ with data destined for a user module which will reco~nize this i~vr~ .tiV~1 by means ot its unique address.
15 Similarly, the user modules transmit ."~S.Sa~133 to a node d~ s3~d for the node itself or another user module. Part of the i, ", h tldll by each node is the periodic tldll .ll , of reference packets which are received by the user modules. The bit enor rate or other merit factor ~ s~ with tile reception of the reference packets 20 along with the si~nal strength is utilized in the antenna selection process which will be described below.
In FIG. 3 Table 24 consists of a matrix of numerical values which reflect a rankin~ of the antenna pattems, i.e. different antenna in this h~i",er~t. A separate value is c~ i for each of the ~"~;" ~s 25 of antennas tor a user module and a node, i.e. user module antennas 1 i-6i and node antennas 1j-6j. In the illustrative c "L,ovi",~nt, each user module maintains such a matrix for each node with which it can communicate. In the system as shown in FIG. 1, UM3 would maintain a separate matrix for N1 and N2; the other UM's would maintain a single 30 matrix for the ,u~pe~ nodes.
Each user module generates a Table for each node with which it can communicate upon bein~ put into service in such a system. In this system nodes and user modules utilize half duplex communications by sending i,,lur, 1 to each other. User modules preferably ~enerate WO 92/13398 , PCl/US91/07695 - 209~57~

the values for the matrix based upon data teceived from each node. The node transmits the reference packets of data F ~ usin~ each of its antennas 1j-6j and the user module receives the lldl~Sl,litle~d signals by peric '1~ selecting each of its antennas 1 i-6i. Thus, after 36 such 5 comrnunications Table 24 will have values for each cell. In a relatively hi~h speed communications system, such as utilizin~ packet llal~sl~ .z.;.)n techniques, lldll ... 1~ and receiving the required re~erence signals to complete the Table can be a~llll,l;shed in a relatively short time.
The c~ n of the value ~or each cell in Table 24 is based on si~nal auality (Q) and signal Strength (S) ot the re~erence si~nal received by a user module antenna trom a node antenna. Each received reference signal has a new rank (R) cPI~.II' ' ' as follows:
(1) R 5 (qa)+(ssj where q and s represent numerical weighting factors allowing the signal quaiity to be weighted differently than the signal strength. The selection of each of these weighting factors will be ~ dl dep6ndell~ upon the 20 communications system and the dl ---r ' rl ell~/ .UlllllCtllt. In a preferred e...~di",6r,t of the present invention, the signal quality has a su~ald" 'Iy greater ;",~,ollance than the signal strength and thus q>~s, i.e. q~lOs. A c~".~, ~al RF signal level sensin~ measurement may be utilized for si~nal strength. The signal quality may be measured by 25 d~lt~n,l;" 19 how many lldnsl";lt~d symbols exceed a pr~uturlll;,lad receiver demodulation window or may be based upcn other known signal quality type measurements such as bit error rate.
The historical rank (HR) of the signal for each cell in the matrix is the value stored in Table 24 and may be ~: ",;.,ed as follows:
3û
(2) HR = (k-HR) + ((1-k)-R) Where k is a weighting factor which weights the historical rating HR relativeto a newly calculated new rating R, where 1~k~0. In the wo92/13398 PCI/US91/0769~
20q8578 preferred ~"II,odi",er,~ the historical rank is wei~med su~ald, 'Iy higher than the new rank to prevent rapid chan~es in the cell value i.e. k>0.5 such as k=0.9. This places more emphasis on the past history than on the current calculation. This does not introduce an excessive delay in selectin~ a different antenna when the table HR values are updated frequently such as every 24 - ~nda. As will be described in more detail below at least portions of this Table are bein~ continually updated to take into account a changing t,~ r""~,lt or other ~actors.
After each user module co", ~ a Table 24 for each of the nodes with which it cdn communicate, the user module makes a d~ ~.r",;" ~n of the best node antenna. This J~' .111;11 "~n is nal.,ilL~d from the user module to each respective node thereby informing the node which of its antennas to use when communicating with the user module. The user module antenna to be utilized for each node is selected at the user module based uporl the Table. Since the Table at the user module is based upon signals received from a node, it will be apparent to those skilled in the art that this system relies upon the principle of Itn;i~.,~ity in making the node antenna selection i.e. it is assumed that the best antenna for ~Idl lalllilt;l1~ from the node to the UM is also the best antenna for receiving signals from the user module. The antenna selection method accordin~ to the present invention allows additional user modules to be installed s~hseql~snt to initial system csll'ig Ir:lti~n with automatic reconfiguration and selection of the hest antenna choices.
FIG. 4 is a flow diagram illustrating the initial ~en~' n of values for Table 24. Beginning at the START 26 variables n and i are set to 1 in steps 28 and 30. The variable n t".r~s~ the number of times the entire Table has been ~ and i l~ a~ ;, each user module antenna. in step 32 the reception of reference packets used for quality and signal strength d~l~llll;,l ~ is enabled on local antenna i. In step 34 pdldlll~t~l j is initialized to 1; j t",re,s~"~a each node antennae. In step 36 the user module constnucting the subject Table enables reception of a reference packet lldl~lll from node antenna j. Step 38 ,t,~r,,s~"l;, a time delay allowed for the user module to receive the WO 92~13398 PCI/US91/07695 ~ - ~0 985 78 reference packet from the node. in step 40 a dedsion is made as to whether a new reference packet has been received. If YES, the new rank R of the received reference packet is calculated in step 42. If NO, the new rank is set equal to WORST which ,~,t,se"t~ the worst possible 5 new ranhn~ a~;$~"abla to a cell. Such a value is assigned to represent an unusable antenna co,.lL,;,~ 'i~ ) since the reference packet was not received at all. The histofical rank for the particular user module antenna and node antenna c~"lL,;r ) is calculated at step 46. The historical rating HR for each of the cells is stored in memory and is used for 10 selectins the user module and node antenna to be utilized as will be descfibed below.
In step 48, variable j is ill~,lalllf~ll by 1 thereby selectin~ the neYt node antenna to be utilized. A decision is made by step 50 to detemmine if the value of j exceeds the actual number of node antennas. A YES
15 ~f `I ",;. `i~ ) indicates it is within the maximum number of node antennas and steps 36-48 are repeated utilizing the same local antenna i but new node antenna j. A NO ' '.~ ion by step 50 indicates that the UM has had the opportunity to receive a . ~f~ clod packet ~,a,~:.",;llad from each of the node antennae, usin~ the same local UM
20 antenna and the user module antenna i is ;II- lnlllfol `~-' by 1 in step 52.
Dedsion step 54 '~ f~ if the value i is within the maximum number of user module antennas. If YES, steps 32-52 are repeated in which the i user module antenna receives reference packets from each of the node antennas i- A NO '~ ",;.,dti~n by step 54 means that each of the node 25 antennas has t~d";"l.;;;~d to each of the user module antennas thereby c~"",l~ a sample for each of the cells in Table 24. The variable n is then i~ ."~,~ ' by 1 in step 56. To avoid mahng an antenna dedsion based upon only one sample of each cell and to build a history of such cell values before mahng the initial antenna ~ ",;"dtion, decision step 30 58 cl~t...lll;ll,os if a suflicient number of samples of each of the cell values in Table 24 has occurred. If n has not yet achieved the required number of samples, a YES decision causes steps 30-56 to be reqYecl ~ ~ thereby ger,~,d~;"~ another series of cell updates for the entire Table. A NO
~ ~ern,;"dliol1 by step 58 le,c,~,se"~s that the p,. 't: r",;"ad numb~r of WO92/13398 ` PCI~US91/07695 2098~78 g Table samples has been reached. This series of steps l~"";.,ttas as indicated by transferto ~A~ 60. The pa,d", n will vary depen.lin~
upon the system configuration and the relative i"",oltance placed upon the historical si~ icance of th3 values of each cell in Table 24. In the 5 illustrative ~ bGu;-llelllt of the present invention n is desirably greater than 10 and is preferably greaterthan 50 due to the emphasis on historical wei~hting.
FIG. 5 begins at entry point A 60 where variaoles j and i are each initialized to 1 I.,~r.,a~" ~ node antenna 1j, UM antenna 1i at steps 62 and 64. Step 66 in CGillLi, 1 with steps 68 and 70 generate a value equal to the sum of the values in column 1j. This column summation I~,rus~"ta a c~-~ value of the overall p~rfur",ance of each node antenna. D~ ",ir ~ step 70 ceases looping back to step 66 when all of the values ~Cco~; ' 3t! with each of the UM antennas has been 15 summed for one node antenna. Step 72 selects the next node antenna to have a column summation of HR values. Decision step 74 causes the preceding process to continue thereby summing each of the columns ,~,r~.c.c., ,~ node antenna values until all of the node antennas have a C~r,~a~or, ~9 colll,l~o~:h summation. A NO d~ ~ r",;., J~ by decision step 74 indicates that all node antennas have s~ s that have been r~ ll' ' ' In step 76, the node antenna with the c~",~,us;~
summation j of the BEST sum identifies the node antenna to be utilized for communication with the cOIl~apol7d;,l~ user module. Step 77 ranks the UM antennae trom best to worst based on the column in Table 24 a~ ~ with the registered or used node antenna. In step 78 the user module transmits the j node antenna selected to the node by a packet trom the user module to the node. Thus the node now knows which of its antennas to assign when communicating with this particular user module. The steps end at point ~B~ 80.
These steps are carried out at each user module for each node with which it can communicate. Thus, a Table 24 will be calculated for each node that can be ~seen~ by a user module. Although each node does not maintain a Table 24 it maintains in memory the antenna assigned to it by each user module for communications.

WO 92/13398 PCr/US9~/07695 2~98~7~
. .

FIG. 6 is a flow diagram of an ex~l"~,làiy method in a~r~ia-,~e with the present invention for d~ and continuously ~ )g the best user module antenna. Before beginnin5i these steps at point ~B~
80, values for each cell in Table 24 wil! have been calculated and a node 5 antenna selected. P~lal~. ' . n, j, and i are initialized to 1 by steps 82 and 84. Pdlall. `t a i and j refer to user module antennas and node ântennas, ~ c'i.~'y. r~ra.- ~ n will be explained below.
The reception of reference packets from node antenna j on local antenna i is enabled at step 86. A time delay is ;- ,'r~ 1~ csd by step 88 to 10 provide time for reception of the reference packet. Decision step 90 dtlI~. ",' ~es if a new reference packet was received. If NO, then the new rank R for the user module and node antenna ~,,IL.;n ~' ~ is set equal to WORST, i.e. a very low rating value. Upon a YES dedsion by step 90 a new ranking is calculated by step 98. In step 100 the historical rank HR
15 for the subject antenna OO...~ ' n is updated to reflect the iatest new ranking.
Decision step 101 ~ ";nes if all node antennae j have been sampled. If YES then step 103 ;"c,t,--,~,lts j and steps 86-100 repeat for the new node antenna. If NO by step 101, then decision step 102 20 `~ -...;,.as if any user module antennas remain to be evaiuated in a cycle in which each of the antennas are 6~?'~1 ' A YES decision indicating more antennas are to be evaluated, causes step 104 to ~ncrement the user module antenna pdldlll '~ i and a C~hse~l'snt re-evaluation for that antenna by steps 86-100. A NO decision by step 102 2~ indicates that all antennas have been reevaluated in a given cycle and the user module antennas are ranked from best to worst for the values in the column of Table 24 c~ ,o"d;"g to the selected node antenna by step 106. The previous ranh'ngs for the user module antennae are "~ ' ~' ' ,ed in memory. Decision step 108 t' ' "-;"es if the latest 30 ranking e~ s~"ts a change in orcier for the best rated user module antenna. If YES, the local antenna is chan~ed to the current best rated antenna by step 110. Followin~ a NO decision by step 108 or following action by step 1 10, decision step 112 d~ltn",;,)es if the paldll~ ( n equals a prt,d~t6" ' ,ed value. This p,. ~ .II-;"~d value is selected wo 9Z/13398 . PCI/US91/07695 -11- ~;
such that the node antenna will be reevaluated less ~requently than the evaluation of the user module antennas. For example, if n = 50, the node antennas would be r~ .,' only after the user module antennas have been reevaluated 50 times. If the value ~f n has not yet reached 5 this ~r.~ ", led evaluation value, i.e. a NO decision by step 112 alllular n is i,-~ " ~ by step 114 and another cycle of user module antenna evaluations occur by steps 86-110. A YES decision by step 112 causes the node antenna to be reevaluated by going to point ~C~ 116. .
SL!bjecting people to prolonged radiation from the user module is avoided by the continuous ~ process used in selecting the active user module antenna Referring to FIG. 1, as a person enters area 11A which cci"~ ,uriJ~ to the active antenna for UM3 the user module will be reevaluating its antennae. Because a person enterin~ this limited distance zone wch as a maximum of 1 or 2 meters from UM3 will S~,la" ~ alter and likely degrade the ~rvpa~dtiull of signals between UM3 and N1 the method according to FIG. 6 will cause another antenna at UM3 to be selected. When used iri a packet signalling system having very short packet lengths relative to the normal speed at which a person moves this method will cause another antenna to be selected within a few seconds thereby ,ilr,iLi,.g radiation exposure.
FIG. 7 is a flow diagram of an illustrative ~ tJud~ llt of steps in accv,dd"ce with the present invention by which the selected node antenna is continuously ro~v^' ~~ I Beginnin~ at ~C~ 116, F - ~ i and j are initialized to 1 by steps 118 and 120. Step 122 calculates a lon~ term historical ratin~ (LTHR) which is calculated in a similar manner to the historical rating (HR) previously defined. In this calculation the wei~hting factor K may be selected to be different than the weighting factor k for HR. This r~ n step creates arlothsr table similar to Table 24 havin~ the same format as Table 24 but ,~",res~" ,~ an even longer tsrm average of the values in Table 24. This table is utilized to provide an even greater historical weighting to the ~ J n of the node antenna to be utilized. It should be ,~i"~."L.~rt,~ that Table 24 will have Deon cre~ed ltnd u_ed e nlJmbltr ~ times behbre the l~n~ term .' 2.~.~g5~ ~

historical rating ~ ' n in step 122 is made. Steps 124, 126,128, and 130 combine with steps 120 and 122 to form a calculation nest by which each of the possible user module antennas and node antennas are reevaluated for the long term historical rating table. A YES
5 d~telr~ ld~iol~ by step 128 l~ l ,ts that each of these c~ ' na has been made. In step 132 a decision is made on whether the node antenna should be u~,v'~ The decision criteria to cause a node antenna .~ s '~ ~ (YES), requires that the historical ratin~ for the selected use~ module and node antennae be less than a short term (ST) 10 threshold and that~he long terrn historical rating for a selected antenna c~",L.;" n be less than a lon~ term (LT) threshold. It should be noted that both the HR and LTHR re~ ..".,-~t~ must be met. In the reference to LTHR [Il, J] the ll refers to the best long temm value for a UM antenna in the registered J node antenna column in the long term table. It will be 15 ~,u~,r~.,idtad that for a given node antenna, the best UM antenna i in the HR table may be different from the UM antenna ll in the LTHR table.
Different ~ .h~ld~ for each requirement can be selected to take into ~,~;,idt~ n the speciflc system configuration and e~ .u,--"~-~t. A YES
~' : ", ,d~iùn by step 132 causes a retum to point A60 and r.s s ~ !e 'ic 1 of 20 a node antenna. A NO d~ttelllll;,l ~, causes a retum to point ~B~ 8û
resulting in the continued reevaluation of user module antennas.
Subjecting people to prolonged radiation from the node is avoided by the continuous reevaluation process used in selectin~ the active node antenna. In the preferred a."L,udi",e"lt the node has the same type 25 di,~ ' antennae and effective radiated power as the user modules.
Thus areas similar to those shown for UM3 in FIG. 1 exist relative to each node antennae. Because a person entering the limited distance zone adjacent the node will suL,~ r alter and likely degrade the ~u~Jagatiùn of signals between N1 and a user module, the method 30 according to FIG. 7 will cause another antenna at N1 to be selected.
When used in a packet signallin~ system having very short packet lengths ~elative to the nommal speed at which a person moves this method will cause another antenna to be selected within a few seconds thereby ",." "i~ g radiation exposure. Althou~h the antenna ~'VO 9~/13398 _ PCl'~US9~rO7695 ~098578 ,- 3~ 'ic ~ m~thod according to FIG. 7 will be slower than that for a user module, it w~ll still be fast enough to prevent any prolonged radiation of a person within an active area. Also, since the nodes are desirably placed at a central location relative to the users and at a hi~h location in 5 a room or building such as on the ceiling or on a support preferably at least 7 feet above the floor, it is ~ess likely that people would normally occupy the defined radiation areas.
It is believed to be appar~nt to those skilled in the art that the illustrative method relating to antenna pattem selection can be 10 adv~ o,Jsly employed as part ot an overall operating system utilized to control other pdldll ' ~a and communications in an RF communication system. This method or selected parts of this method may be integrated into a central control pro~ram and may be carried out as background ùp6rdlions as time pemmits relative to other unintenuptable or priority 15 tasks. Once basic communication is e~ dd between a user module and node, the continuing rss~ on of the proper antennas to be utilized may not be critical d~pel,.3;.1~ upon the operating o.~-;,u"",a"l.
In the illustrative c.,lbGdi"lt,ll~, each user module contains a table 24 of values and a cul-~a,uonclil~g long term table of values for each node 20 with which it can communicate. In the illustrative half-duplex communications systems shown in FIG. 1 it is believed aclv~ d~eo.ls to have the user modules make antenna selection ~ " ,.,;., )~s since such '~ .", ''-~la can be carriQd out in parallel based upon a single lld"a,l.;saion from a node. This method also facilitates the joining of a 25 new user module into an existing system since the c~""pl~,~it~ relating to antenna selection is distributed among the user modules and not c~ n.~ at the nodes.
One of the advantages of this invention is its ability to select the most dp~lupridl~ antennae for use without requirin~ ! -' ' '' of the RF
30 lldl);,C~ ,ra. Selection of the antenna to be used is based on relativè
wllll~dliaUlla.
A further advantage of this invention is its ability to minimize a person's exposure to RF radiation. In the illustrative e"ll,~Ji",~ of the invention the disnuption of the ~lupa~dliùn of signals between a UM and oqss7s . -14-a node is used as the means ~or limitin~ exposure to radiation within a defined area. Other means for limiting radiation exposure also be utilized. A low trequency amplltude moduiation detector that is E'- `r' 'Iy at or near the ~d,~s,~ ar as it feeds the antenna could be 5 used to detect the Doppler shift between the lldll_ "' .I si~nal and the scho from a nearby moving object (person). Such a detection would be us6td to cause the selection of another antenna. A' , ~ , a detection system could be employed that would be i"depend~"t of the 1l.ll- ,"l si~nal. An ultrasonic detector or an infrared ~heat) detector could be 10 used to sense the ",oJ6 3nt or proximity of a person. ~, " 'y such an i,.~epend6r,l detector(s) would have a di,.",tional capability consistent with the di.~- tional ~ .t~liatics of the RF antennae so that antenna switchin~ decisions could be easily made.
Although an 6~ udi..l~rlt of the present invention has been shown 15 and illustrated in the drawingâ, the scope of the invention is defined by the claims which fo lo~.
.

Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A radio frequency (RF) remote module (RM) capable of RF communication with a communications system comprising:
means for selecting an RM antenna pattern from a plurality of directional antenna patterns that cover different geographic areas relative to the RM;
means for periodically generating a signal quality ranking for a plurality of remote device antenna patterns for said RM based on signals communicated between the RM and the communications system;
said selecting means selecting the RM antenna pattern having the best quality rank for communications between the RM and the communications system;
means coupled to said selecting means for limiting a person's exposure to RF radiation from said RM when the person is within a predetermined area adjacent said RM.

2. The remote module according to claim 1, further comprising means for determining the quality (Q) of signals received from the communications system on each of said antenna patterns;
means for determining the strength (S) of the signals received from the communications system on each of said antenna patterns;
means for ranking each of said antenna patterns according to R= (q*Q) + (s*S) where R is the rank, q and s are numerical weighting factors;
said selecting means selecting the antenna pattern for use in communicating with the node based on said rankings.

3. The remote device according to claim 1 further comprising means for generating a historical average rank for each of said antenna patterns according to HR=(k*HR) +(1-K)*R, where HR is the historical average rank, and 1>K>O, said selecting means selecting the antenna pattern for use in communicating with the communications system based on said historical average rank .

4. The remote device according to claim 1 further comprising means for periodically generating new rankings R based on new determinations of quality (Q) and strength (S).

5. In a radio frequency (RF) communications system having a remote module (RM) capable of RF
communications, a method of limiting a person's exposure to RF energy transmitted by the RM comprising the steps of:
selecting an RM antenna pattern from a plurality of directional antenna patterns that cover different geographic areas relative to the RM;
periodically generating a signal quality ranking for a plurality of remote device antenna patterns for said RM based on signals communicated between the RM and the communications system;
said selecting step selecting the RM antenna pattern having the best quality rank for communications between the RM and the communications system;
limiting a person's exposure to RF radiation from said RM when the person is within a predetermined area adjacent said RM.

6. A method according to claim 5 comprising:

determining the quality (Q) of signals received from the communications system on each of said antenna patterns;
determining the strength (S) of the signals received from the communications system on each of said antenna patterns;
ranking each of said antenna patterns according to R= (q*Q) + (s*S) where R is the rank, q and s are numerical weighting factors;
selecting the antenna pattern for use in communicating with the communications system based on the highest rank.

7. The method according to claim 6 further comprising the step of generating a historical average rank for each of said antenna patterns according to HR=(k*HR)+(1-k)*R, where HR is the historical average rank, and k is a weighting factor where 1>k>0, selecting the antenna pattern for use in communicating with the communications system having the highest historical average rank.