Note: Descriptions are shown in the official language in which they were submitted.
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
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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.
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~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.
;
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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
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",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
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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
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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
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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
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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
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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.
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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
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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
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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
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,- 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
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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~.
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