CA2432347C - Multi-beam tdma satellite mobile communications system - Google Patents
Multi-beam tdma satellite mobile communications system Download PDFInfo
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- CA2432347C CA2432347C CA002432347A CA2432347A CA2432347C CA 2432347 C CA2432347 C CA 2432347C CA 002432347 A CA002432347 A CA 002432347A CA 2432347 A CA2432347 A CA 2432347A CA 2432347 C CA2432347 C CA 2432347C
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Abstract
An earth station (8) receives a return signal (3) via more than one satellite link (4a, 4b) from a mobile terminal (2) using TDMA.
The earth station (8) selects one or more of the satellite links (4a) for transmitting a forward signal (15) on the basis of the quality of signal (3; 15) received via each link. The earth section (8) allocates frequency channels to the mobile terminals (2) according to their location on the surface of the earth, so that the propagation time to and from those mobile terminals (2) which share the same frequency channel is approximately the same. The satellite (4a; 4b) includes an antenna which generates an array of beams which are individually pointed to fixed regions of the earth, until the elevation of the satellite (4a; 4b) relative to a fixed region falls below a minimum value, in which case the corresponding beam is redirected to a new area, while the other beams remain pointed at the corresponding fixed areas. In this way, beam-to-beam handover is reduced, while maintaining the boresight of the antenna pointing at the nadir.
The earth station (8) selects one or more of the satellite links (4a) for transmitting a forward signal (15) on the basis of the quality of signal (3; 15) received via each link. The earth section (8) allocates frequency channels to the mobile terminals (2) according to their location on the surface of the earth, so that the propagation time to and from those mobile terminals (2) which share the same frequency channel is approximately the same. The satellite (4a; 4b) includes an antenna which generates an array of beams which are individually pointed to fixed regions of the earth, until the elevation of the satellite (4a; 4b) relative to a fixed region falls below a minimum value, in which case the corresponding beam is redirected to a new area, while the other beams remain pointed at the corresponding fixed areas. In this way, beam-to-beam handover is reduced, while maintaining the boresight of the antenna pointing at the nadir.
Description
~ WO 96103814 ~ 02432347 2003-06-27 PCI°lGB95101103 t -s P
Multi-Beam TDt~A Satellite Mooile Communications System T~C:~NICAL ~'°:L~
The rresent inveraticn r a l a tes to a ~et.hcd and acbara tus ~ or counica tron via sa to l l i to , and ~n particulad but nct exclusively m ~ voice oy data communication using non-geostotdcna~T sate~lites and/ or ~ob~le te~~.nal s .
B ~ CKGROU~ID ? R'~'°
In eomaunica tion sys ~.e~s ~iz~.c h use non IO geostationaa~, satea~ i.tes, the nu~.:e~ and crie:°~tat~on o~: satell~'es ~n vi,e.~r c~ a ga cund~°based tei:~a1 va~°ies dug ~ng a ca 1 ~. a I'ls.~.s , the eu~.:,°~unicoa t~cn lmnk between the ~e~~':a.e ~,~ed a.:y CSne s c..'~''~~~~ 'Wa '.flay a~eeCCu'Ze weakev as the e~evatien angle cd the sate~L~~a decmeases and u~.t~.~a te~.v t..he ~~.r~c ~~ay be;~c~e .'..Ild'~eT~~a~~ a as t:'~~ sc°1~~1_!~ :>~c i~C.~'sl~~ .'",~1~~~.
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t., ~=.e~:~ia~ial az~d a ~a:~°tize~~~ a~° s~.~_~.~? ~.:~.r~~ ~.~aza ~~~~~o ' ' WO 96!03814 ~ 02432347 2003-06-27 pCTIGB95l0I I03 ' 2 obstruc~ed by buildings, trees Qr other obs;.aci es as '., a the terminal er the sate!! i to :coves during a call.
This ef=ec~ is known as "blockage°', and reads to i fading =n the received signal.
Sicnal fading may also occur when a signal transmitted by a satellite is ref? ec-ed off the grcund a or bui' d;ngs and th a ref lee red s ~.grar is received at the te~~.nal tcge they w~eth °he dir p : r s bgnal . The chase d if er ence between the d~.rec= and :: ef leered IO s ignal s may lead to des trucrive ~.r~ :.er f erence a c the '~,.=_r'~i~Ya' , sG~ t~3c~ w. '~,~~~ z '.'~,:e T~.ve~, s.>.cnam S tr eng'h iS
d reduced. This is ~~~c~w~~ as °':~~.i ~.~~.,~~H~° fadi.~.~.
The ~C.'c'~a'°°le:lt ~1(~°°~...C~~ ~4;>i'd ~m.s'~.',~.;...~e°aG'~:a a ~as.e;.~'~,d.e ' communica tion svs te:n in which th a sa ~eil.ites zaonitor the cua~it°: of si.gria~, ~°ece~.ved r~:c;~ a tpina' and determine wh°.cJ' c~~ie ~5 ~~es~ sr~i~.uc:~, ;~; han~,~.e she ca~.:~
~:o the ~e~.:~~a? ., care ref the say a ~" ~ ~. ;yes w~e.,.~~ azami is , the signal recei°~red f.~ em the ~:e.°.inah ~o ~ther satellites or gateways. i 2 Q 'the conf er enc~~3 ~a~er reThe C~~~9c~ba 1 s ta~° ~'obi~ a ~at~.~:.~..~.be ~~,~i'~~C~~. L°5~~2,~ ~~c:"'~.GX''al.C~~ ~e<"~GI"~~..1 ~~~lunq.c~~°.~.~.7~~"' ~~ ~il~.~~',~~~,:sb~P7. a1'x~=- ~J,.~..e~~l,y ~rt%
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~ys te~~s3 ~,n Zsi~, ~.~~'I ~~.'''~~~~:i~ ~",.:t.:'~,..SS;. ~.~.~?1~;. ~.e i?.:L,'f b.°e:°~'.1.~E?.'~ ~~' two or three sate~...lates; e~atec~a~% ~E.:~;p.~a~~s me2~su~°e tY~
CVO 96103814 PCTIG$9510I103 ' 3 signal lever e. each of these alternate paths and control which s~r~'~.al paths are used. This systen is exclusively desicned for use wi~h code-divided nultiple access (COMA).
However , COMA suf f ers fr ors a nu,~::er of dr awbacrs when used for mcbile com.~°nunica~.~.ors. The nobile terminal s are complex, since they rec~~ire a separate decoder for eacsatel life path. :~c:~°eover , COl~.x~ is inefficient in =recuency re-use unless the users are IO evenly dsstd ibuted, and p~~rer level s canno;~ be 4r eel y varied for each user witk~o~:~t ca.us:.~yac~ ~.nter'erea~ce for other user s . : u~ ~~xeor~ s a.~~u ~ ør ~.ca~ ~ i:ate~ f pr ence takes gal ace at cea:~c level s of use c~r~'r '~'~t'ti::~T'T_' 0 ~ '~'~° =° ~'_W~':~t'~'TOId S ~.cc: rd~.ng ~c one aspect of the p.°esen~. i.~:veo".iot2, t~:ere .:.s o~:cvidec~b a me~hr~d r.~f cc~~~;s'a.va~,vc~r~ e~:~eeev a ~°~°~'e~~~:.<'"°..d' s~~':,',.'..C3°1 aTlC:~ a ?J,.L~~"~.S~T.~.~d Ca f' ~:~a.d'1~.~,:'~~~W L'~~,'l.~iC
TDl~ t.r~ address each ~:~ the ~:er~mTxa? s =row t.'~e te~~'e~°~b'~.yd~ sta;:~,~°l, In WtI~.C~"~
d~.~le'"°~3.w.°.~ 3_s pW°~yJ~.~.~'c3. ,~~1 C t~~ ~..~xlk. ~et:de~ri ~h~ to ~'~ ~~ t'," ~.~ ~.. s ~.~'~'. bO22 ~~~C~
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x . ~ ~-, s s~~ cat. ~.h~~u~h ; ;-ee ~.w~ cap; ~co~'e sa~~c~~.~ ....~~s, ~;~ Aaav be ~~e~.~u ~.xr c~~~,f~e~ea~~; ~.:~~~:~ WI:~~~a:.~ .
In this way, blockage may tae a ~~,uced w b~:h~s~ the CA 02432347 2003-06-27 ' 6V0 96103814 ~C'TIGB95101I03 a inherent disadvantages of CDMA.
The terrestrial station may either deccde the bes t received signal fr ~ra each te~~..~.al or zaay combi ne all cf the received signals to reduce err:;r in the received s ignal . The ter r es ti is l s 'a'tien may then select a fa~~~rard 1 ink tc each terminal t~'~rough one er more of the sate? l ites according ~o t~e ~xali.y of signal rec~ived frcz~ the term'_nal thrrugh the satel li tes .
0 Thus, a smooth handcver ~zay be ach~eved and blockage a~~ri fading zzzay be r ~d~z.c~e~'~.
4.n o~'der t~~a~.. ~l~e 5~.:mea~»~ia~ ~.n ~~t~?'..ate fvr the f0~"~Ir'3~'d .~'..'sl~C: :~a~y be tJ:~Ils~:Ja.:"°~b~ t;: r:ee t=
~°r.na~, the ter r es tr ial s to tion znay calcul a to the delay i:, the l~ td az~s~'.~ss ~c~~ ~~a the sel ec t..ed sate~.~..~:.e and ady;s t the sage ~:~,me s~.ot th~cug~~c~ut the cal' . The c~.l c~.~l atic~n may ta~.e in~c~ accc~.znt ~acth the va:~ia.ticz~ iz~ de~oay as the ;-~~.~. '~C'v'C:~!'~ ~'ac ~'.~.7..~.~.'~'.r~.~ i~.c,'~'~1~ a ~~' 1.r!.;~:s.Vr~ C:, CI ',al.E? ~q~~L ~8 c'~.dl~. ''~,'.i'~C, t~~.E.~°:!'°d~'1G~:~ .~~°l, t;~i~',LcA~%' ~.~~-~E'T"S ~rt:'~C~.~,oxr-°~'' ~t'y'~,~ ~',y4~~i C'~~~~e i .. lw, ~ .,~ ,.~ :.. :. L.~, ~ ~ R
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a~~, ~~i~C~i'~.cx~f~m~~" ~'~1'~C~ C~:~:~~L~x.~:k ~.3.~G~L~.~~'~'~~' r'.~ tbt~~~'. Ym~.~L~,..l:'~~~. Y_~r. ~:~'J:C:
yr:,~~j,~~RxG)..~.:, .~.Z'j. 'e~'C~,~X.~.ig.'s;C~it;, ~'~°1~.~,~am'v°'~,'~xr~r..:'~<..;.. ~ri~',~~:d>C:)~E his.
c~a~~en~a~:e fC~~'' the ~C~~a~:~eY° si.ia~~-~. ~..~'~ tk~.~: sig-rxa?..
w~ 96~~38~~ CA 02432347 2003-06-27 pC.Iy~gg~dI103 ' S
received from the terminal and adjust ~he freguency of the trans:aitted signal accordingly so that the terminal r eceives a s ~gna~. a ~. a constant fr ecruencv tl'zroughout a cal=. The Dcpgler shit t may be pa= tial ly cnmoensated for by the satellites.
According to another aspect ef the present inven Lion, in order to f ac=1 i to t= s=mul taneous communication wath multipla users through one sate? lite, ar eas of the earth ar a divided into a number of fixes regions, with , a arecuency being assigned to a ~er:~~ ~,al bath for ~.m ans~ission and recept~son of sicnals ac::ord.i..ng ~.o the :.°egior.: in wr~.ch the ter~nmnal is 1 coated . The 1 ocati~~.s of the a rc ions are deterained ac:.ording to their positions on the earth, rather: thar', thei~ g~~sit.ions ~eiati~re 'o the sae? 1_ite> ~mmu? ~.araeous coud ~..crt.ion between d.~fe~'~.~z~~, ~.- ~ra~,.~z~.~.s ~.~ the sazz~.e rec'~..c~~: ~.r~d a;~: th4a same f r er~ueg~~s.~ es ~~ay ~~e a~~~ 2.,evec~ b~' al? race tinc~~ d~.f f e4 ~~a~
t.
t~me slots wit.:~mn a repeating time frame to each of ZQ t~s3e 4 ~""C~b:,,~.nl~~.'"~ , ~.~":r'~C>'fw ~' ~r~~ ~' ~"~'~'re~ i_ ~."=.m"~°."~.~~"R~~1.~ a~~~~'b~9 °~, ~~~fg~. ~''':!,'~t~~~P~~aY',t:.. ~ F3:a ~K.','E,.-'' ~:~P~.~~
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WO 9610381.1 PCTIGB95/01103 a a nen-ge~stationary satellite which generates a plurality of individually steerable beams to provide communica Liens ? in)cs , in which each beam is dir ec Led towar ds a f fixed r egion a r the err th' s suv ace un til the beam is no longer sui table f or co,:~un_cation caith that 'fixed region as a resist o~ the 'prcc;ress of the sa to l l i to r a l a t=ve to the ear th' s sur _-'ace . ~':~e beam is then red~.r ec°ed to a rew f zxe~' r ecion with which saris°actorr comaunicaticn is possible. Calls to the pr'nv~ous ~ fixed region may be r oared t~.r cugh another satellite.
~r. 'h~.s Way; the =~°egue.:~cv o~ beam-to~pbeam handcver may be r edF~.ced, w i t:~ou t a.~ ec t:.a~~ the f regt.:ercy o 'f sate l ? i re-to-sa to l l i re h andover .
L5 '~'"he presen t ma~ven'~.ion ex wens to a :.er= es ~..r is 1 sta~.can having means ~.o~. per°o.~.n~ ;.he ~a:°lcc~.ons o:~.
yw ..~. ~ .~ mo b s,. .~... y r ~ 5 ~ ~ r descr ibed aho~re .
BFW~'= DB'SC~I'~'~''1°QT\t ~~° mxr~; D~.~WTN~S
Specg.L~=_c' e~~_t~~c~.~ei:~~-.s o~: '~.he p:~eser.t inve~ation w.i.J~~~ P~c~~~ ~~; c~~ c::~.:~~:;e.~. w~..~°~~.tv~ :~r~r~=ar~~c~~:
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~'~.:~1"Lt°°~. ~. ~.~ ~4:~~. ~LE':uiw~:~,.~;. ~"3 i x"7t~'~
d~a~'~,xt1 C.7 ~° Cs~'~.e f'c~'~ra~~d a~~~ r~:~:.u~.°xa :~.:~~v~~,A ~,e'',~°~reez <:~.~, earth. s~ata,c~~~ ~.x~d.
2S a mcb~~le ~:e~:~~.:~_x~~,~
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'' 7 a?ternative paths between the earvh station and the aobile terminal;
F iguy~e 3 is a schematic diacra:~ er the ea~~h s ration;
Figure 4 is a schematic diagram. a~ the mobile terminal;
F igur a :, is a schema tic diagr a:~ c. one of the sateii ites;
Figure 5 is a diagram cf the vorwat o~ ~or-,~ard 1~ and return packs t.s Within a ~r a:ae actor ding to a g:.r s t embodiment;
W~.. a ~ slwows the ar r av~e~eii w - 01 s~~i v be.arji ~~'Cr..'7r?n's oI1 the ~a?~~.hy~ sur~aCe, d 1C~= ° 3 shoWS the ai ~ anCe:3en ~ o '.~, ce 1 ~ S on tile earth's su.~.~°~ace i b the ~irs~~ embed~me::v;
~~"c~wo ~ ~h~~~ h~~J v.h~ ~~~'~s tei°° ~ Sc~~et, ~'a a~e dm~°ec red in tae ~ ~.r sv em~:r~di~en t as t he sa tee? R ~. to pd°o~resses in its o~-b~~.~~;
r ig~.r a 1.0 is a d~.agr am of the ~or~.at of ~o~ ~rarc~
~ 0 ~ . ~' ' < ~ ~. *.
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d s2. ~,~ a C~..~.s~~~~ 2l'!:i~ fix: c~11 ~._~_'~,~~'bl~~..L'ti~ a~r~Ilaw.
~~~.~ ~ ~~a.~° ~-~aao~x~ a,.~a. r' ~.c~~~re ~(~,DES FOR CARRYING OUT THE INVENTION
FIRST ,~1~BODIM~
. A first embodiment of the present invention will now be described ;pith reference to Figures = to 8.
In Figure 1, a terminal 2 of a mobile terminal transmiis a signal 3. The mobile terminal has a '~ substantially omni-directional antenna, so that the transmit~ed signal 3 is received by a first satellite ~4a and a second satellite 4b in' view of tze mobile 10~ 'terminal. The signal 3 is retransmitted =rpm each satellite 4a, 4b as separate signals 3a and 3a. These signals 3a and 3b are received by an earth station 8 ' having first and second receivers sa and sb far receiving signals from the fist and seccnd satellites 4a and 4b respectively. ~ In this embodiment, .-..'~e eart.'~
station 8 has first and second directional antennas directed towards the first and second satel_ites 4a, 4b respectively. Thus, the same information is received~twice by the earth station 8 in the separate ' 20 signals 3a and 3b. The earth station 8 may :herefore select the better of the two signals 3a and 3b, s.g.
' the one with the lowest error rate, for conversion to ' an analog signal for transmission over a public service telephone network (PSTN) 9. Alternatively, if both signals contain errors, data may be derived from both signals to provide a combined signal with fewer or no errors. The combined signal is then analog converted and sent to the PSTN 9.
The earth station 8 also analyses the received signals 3a and 3b to determine which is of better quality. Since there is a strong correlation between the streng',.h o! a return link from oae of the satellites 4a, 4b and the strength of a farwg:d link to the portable terminal 2 through the same satellite 4a:., 4b, ~e earth station a selects ane of the satellites~a~ 4b, for the forward link to the portable terminal 2 and generates a selection signal 10.
When a signal is received from the PSTN 9 far transmissicn to the portable terminal 2, the signal is IS passed to a transmitter 12 in the earth station. Ths transmitter 12 selects one of the satellites 4a, 4b, as shown schematically in Figure 1 by a switch 14, in response to the selection signal 10. In this case, the first satellite 4a is selected as the most suitable for the forward link. The transmitter 12 then transmits a signal 15 to the first satellite 4a, which retransmits the signal as~ a signal 15a to .a receiver 16 of the~mobile terminal. The transmitter ~12 and the receiver 16 may be connected to the same 25 antenna vn the mobile terminal, or to separate antennas. In both cases, the receiving antenna is CA 02432347 2003-06-27 p~'/Ggg5101103 WO 96l038I4 Ip omni-directional and therefore may rec~ive signals from either of the satellites 4a, 4b. Thus, the receiver Io receives a signal '_5 t~:~ ough the s tr onger Link.
~ situation in which blockage occsrs will row be described :rith reverence to Figure 2. This figure shcws a sec tion c f the ear th' s sur f ace on which the ear th station 8 and a ~ucabi 1 ~ terminal Ic~ are located.
The =first and secrnd satellites 4a, ~~r are within the IO line of sight of both t::e each s ration 8 and the mobil a te~ina? I~ . The ang?.e of eleva;._on Ey cf the second sate? T,~> to ~°~b r a 1 a rive t o the mofile :.ei:~al is y~eate,r than the angle ~~ elevation ;, of the direr sate?? ire ~a ar.d the ~aath distances be~ween the earth Sta~~On ~ and the S~~Gin~ SaC~~ ~~.~e 4b, a::d ~eC:de~Il tile ~-'~se0'~nc. Ss'a~:..a"~ 'L~,''~.E, ~~~ ~aI,LV~ ~:~~e ul,t~~")? 1 a tsr::..;~.~:a 7., ~ ~ u''1~'.
S ~'3. (.~" ~''~. "..-~, Y ''.':'~A ~..a~ i;.'~> C;~ S ~'~~ ~;7 a ~°
,~e e:1 Mh ~~? ~.;. ?, r S' t s ~iL a w. ~., ~. 4". ~'a.' ~~ ~'~,. s-'3, ~& ~-..
the mobile terminal 1.~ and ea ~h staticn 8.
~OWever , ~ n ~l',.~~s bas2 th a P'atOD~1 a ta~'.~..:2a1 ~.~ ~s ~C? ~os~.~_.~~ane~~, c<~..c~~e t~~ ~,. t:~:~', c~~a~ .~c.:j.p 20 :auc~ ~.~r ~
c'.r'e~~y.
w~'~~..cy'~> ok~va~~9res -~i~a,~ ~ i...x~~~ c~f s..c~rlv ~ t~ bet~reeoA ,~r.e ~e~b~~
te~."':~:!..5~4'~~. J~~ c'~.~~~ i~.:':3 a ~a.:"..~OneX SasKF:_~-. ~,Je t~' 4b > '~~~lg~'r fd.~~,~"~1 ~hEn ''l~~~~_.~,~~ '(:;F.n.;ii$~.TI "s."f .~.ca '~"'4.~"ct.n<is's~,.~>g;;~ S.
sl~g~G,.,'_. ~ ; 'k',';e,'f~l , Y. ,..
s~.g~2~>~ .~ ~~; c~xi~.y ~r~: ~.:k:l..y ~°~ar°.~~~~~'ed by a-~.e. ~~cw~~:~xr~.
sac:e? 1 ire ~~.~ a.xW vtx~as t~~e ~~pt~~azv~mitred s ~.~<zx~~>1.. ~b ~.s ~iox~e 1 ikel~9 'tc ccr~rain e~:~r ox s . 'the ear ;:.b:~ ~ra~.~:~ox?
a a CA 02432347 2003-06-27 p~j°I~gggI01I03 'OVO 96/03814 selects the firs' satellite 4a as providing a better f or~rard ? ink and tr ans3i is the response signal 1S on? y to the first satell ite 4a. 'his response signa'_ is retransmitted as siCnal ISa to the mobil a terminal I8.
Since the l ine o~ sight la between, the first sated? ite 4a and t a mobil a te~ina? 13 is not ObSC'.LT"'eCi, the response sigrai is recnitred strongly bV t.'~e mobila y ~
~_~-a~inal I8. T'he mobile tw~.,~:al I3 does no°,: ne~d to t a se? ect fro:a ~rhich satr? l ito 4a, 4b _.. is to deceive IO t:~e res~ensa signal lSa, since thus is decided at t.'~e A
a earth sta~ion ~ . Sel e~.°~ic~x of th~a satel lit~s Via, 4b is then ed;,m a t~ axle: ar e~ ~ t;~ the :~r~:om 1 w te=~~_na'_ .
s If, cn the c~her 'xan~., the ~~ci..le te~:.nai a t were to move suc:b that the obstac's 20 no longer a.~ Cb~ true tS 'L...~ a , ine O f a'_~rl t 1:7 , th e'4'e t4 a ea.'. Yh S t3 ,:.~Qn ~ may ~"ec~e~'V'~ a be t ~~~'° S~. ~ z3~~. .~.~ c~~ tLle Sec"~~a°~C~
Sc'~."~e~ ~..~'.°e ~r'~ ~~"3d 6~.''a..:..~> ~s:..~l.~:3:'~'~O"F'E?
.ms's-"'~.-~.~.''O'~ t.~'Ie S~CW:~T"iCC~
satellite 4b for the fcr°~arc~ li.x~.k.
When dif f er en t f rectzencies ad a used f or t.~'Ze ~Ct fc~~;Araw a~ic~ x:a~_~:~.s~ ~~.xv.~~~::,the fa~:~ingis due as:r:, t6~
:~,d:~.~ '~..~.T~~.~-n~ l.n~~~. . t..!' ~s~'13L~~~., C.S ~ (..~'CJ
'~..''.~~I",.~ ~ '~".~'~:'=r"~:! ~ .(~. ~~~' ~4.~~;e~"~~~,~.i.,C~i~ 'Y7~'.~'';~.YE~'~,~,:Cs~a~ t:T:Zd~Ida.~~~~
i~.a:.~' 4:i'lI~ I Y u:.'V ~~ ~f'~E.v:<aa,"'~
.~>"~:.s ~ J"n '~~3.~z.~ ~'~~;~. y. i'".kl.c'~~,'.~k~~.?.X~~~.
'~.:_.'c~Y~."y~.?.,~~,.~~.
xz9>Oi~~,.~Af-~ ~.~
ia~x~cr~xa ~: icon to ~~e e~:~~tb. s c~n ~~:l.at~.rg ~_a t~. ~ ~o ~~e ~7 a~~~~ng'L11 C3.4, ~,.~"~F" ~~-'.~~~~~6~.~, ~b~~.
,eY..'~~oE.''~.~~.''~ ~~,y ~.e~.'131~L~,c~t~..
fx~'~:~m the: ear~"~.~:~ s ta'im ~r~~~ the, ea~''~h sta'~:~r~n g . ~f receives a good retsrn Link signal from the first y t satellite ~a but i:.fcraation trans:.liteed by t.'~e acbile :.
termina_ i3 indica~es that fading is occurring an the f or,~ard link, the ear ~:~ s to tior. 3 may then selec t the satellite from which the next best signal is received for the for-~a=d link. In a case where eac:Z satellite -genera tes seer a 1 over ? a~~ ing beams f or communica tion with mobile ta~_nals at dif f er en ~ f= ecuerC~.es , the ear th s~aticn 8 se=acts ins~sac a d~.~faerer.t :~,eam 1Q generated by vhe fimsL satellite.
The o~ae~a~.? on c~f t~~.e me~b~.~,e ~,~;.nal ~.8 and the earth statian 8 w~.:~?. naw be ewa.~ned w:.t.'~ ~e.~erence tO rte' ~.~Z.m.~ SS ~ p t p ~.:~~.a ~ a FAR'I'T~? S'_"~T?'ON
In t~'1~~ eXc.~,'C~.~'., rlna.~.o~ 5~~.'.eCel ~~.Cnc'31 S a=a r ec~~ Tz~~VPC. a ' ~:'7.~ E?~.'.,° ~'.Le. ~:~ ~°:c"iL..j"CI~.
c3 '_.. C'~ t~e ?c'~'~ 9 i ~~' t~'cin~il~~.~d~rr~"~~3 ~C3 ~~~'. ~."ciC9~'~~~~P: ~~r;.~.~R,.~1_,a ~..~ ~.$ .
r'~.S 5s ~5wT1 In Figure r , the anal v~.e s~oeech s~.g:;jal s are dic~T tizad and encoded bar a cadet ~ ~, and the encoded speech is ~Q COf'1~T~.T~.°te~ y:.3'1'°.;~ a ~~'~'°::..~,c ~J.i.
C~~,'~i.'':~"''~o~ PaC~C'etS c'~.~ ~.
z~ul~..~~g~~.exer~d~:.wu~.t~.~,~___e~r:~°~ ~~.
The tr~~es~~.T~ss:~czn ~.F rt~.e ~~~oke~°~ ~~s concmc~~t.l e~x ~p a. .cc~ni~wMo'l~.er ~~ ~~h~~wc'~ s~~.~:,cts ~~tl~.~.~:~ sa~e~.lite ~ i.~: t~~
be used for he f~.°~~.-~a~~.~,v~ ~H~n.k ~-~n ~°.~,~e basis c~~' the e~ual.i~:v~ of s~,e~~-r~.l re~~~:~v~=e~ f~c~m ~a~:~ Eratellite ~ ~
°~:yhe cc~ntr~~~.? er ~3 c~~c~nt r ca? s a se~.ec°yo*° ~ "~ to send each ij ." W~ 96/03814 ~ PCTlGB95lO1I03 i a i~
packet to one of a z~Lurality of buffers 85a, 85b, 85c.
The timi::g of the output o' eac'.~. buffer 85 is contr o l l ed by the contr o 1 l er 8 8 . '~ he packets eutpu t from the buff=r 35a, 85b, 85c are radio freruencv modulated by corr esponding ~y mcdul a~tor s/demodul ators 86a, 86b, 86c, the frequency of :mcculat ion being cantrolyed by the con~roLl er 88. T he ~..~' signay s are mcdul a fed an dif f er en t fr eCLenC'J DanCS Se.~ec"~.e~ by the controller 88 according to a selec'ed beam o~: the sa ue? li to 4 in ~rhic h the s ignais a~ a to be re-transmitted to the mobile te~i.nal ~ o . The %~° s~.gnal s are transw~~ted b~ direc:t~.o~°ea1 ante::nas 87a, 87b Sic wh ich ar r eacs tear ed 'c~ra~ ds a corm espcnd~.ng satellite ~a, ~b, ~c.
~5 . Eac h m'rect~.ona? antenna 8 i a? a:~ =ecerves signals 4.::~nsl:~.'..~° s b.:~m.ail .°miCJ.~~.:.e a a=:w"aL9'..'°aa.! ~ a'.°d°: ra "~.' ~°~~"~.'~bh '~
~.~k ~ri.'~Ia1 trade. d.W'."..r~;,':.Cee'~cn:;..n~ ~i=~'"sn~..W ~~?,.~r'~,., s',r,r ada:.'~~~.e i:~.~~ ~'t~~~'~".1.C5 fd°eque:~cy demodu~.ated ~y the ~" atodu? ators/
demodul atos 8 6 to fog .r ace ~,~e~ rackets a The :~'a~'s..' 7.~'E?~ ~ a~~e~~~ c'~4 E-~ ~11.~" ' ~.'-~t~~cC~ ~-~i i~.<.e x'71) ~a e~"~ ~j °a ~~'A~',~
~ez~~.~wted °.n c~h~.nne~,s by ~:~t;~.e ~~~rd.~.w~xaT,~:~e~'.l~~em~~~.~:~p:~e:~er 8~ and ~~ee~:~ded b~ faze ~o~3.ec. 8~:~, w~li.~:?T=. ~°.r~~:v ;~'! s~~
p~~~f~~~m a ~°:~c~~° c~aec;~i~zg b~ G_.ompa~~.3.~.f~. ~.,a~:y~.e~=~
~~~~g~.~cAc.~ f~c~l~e ~ c~.~ ~. ~f~ ~ a., % ~ ~,~ e.c ;~. q... n Gad ~ ~< ~ ~' ~: ~ ~...,~., Wh ~:,.~ t,' i ~t.,. ~i a;~. ~~ ~': .~.. ~" .5.. ~4. E'.."~'r ~ c ~~-he resu~.tant analog s:~gnals ax°e sex~r v~,' 'she ~'~a'~ 9 oxz different lines.
The earth station 8 need not be connected directly to the PSTN 9. Instead, earth stations are preferably connected to PSTNs and other fixed and mobile networks through a ground network, as described in patent publications nos. GB-A-2293725 and W096/03814.
MOBILE TERMINAL
As shown in Figure 4, each mobile terminal 18 io includes a microphone 60 in which speech is converted into analog signals. The analog signals are converted to digital signals by an A/D converter 62 and the digital signals are encoded to form the packets by a coder 64. The coded packets are RF
i5 modulated by an RF modulator 66 for transmission from an omnidirectional aerial 68.
Signals received through the aerial 68 are RF
demodulated by a demodulator 70 as received packets.
The received packets are then decoded by a packet 2o decoder 72 to form digital speech signals which are converted to analog speech signals by a D/A converter 74. The analog signals are output to a loudspeaker 76 to produce audible speech. The operation of the mobile terminal 18 is controlled by a control unit 25 59, such as a microprocessor and/or DSP device, which is connected to additional conventional handset components such as a key pad (not shown).
SATELLITE
Referring to Figure 5, each satellite 4 includes an antenna 90 and a beam-forming device 92, which may be a radiating array antenna and a large Butler 5 matrix as described in Patent publication No. GB-A
2288913. The beam-forming device 92 converts signals from each element of the array into signals from a plurality of beams and vice versa. Signals received by the antenna 90 from the mobile terminals 18 are io fed via a control unit 94 to an antenna 96 which retransmits the signals towards the earth station in a frequency band corresponding to the beam in which the signals were received. The antenna 96 may be steered towards the earth station 8. Likewise, i5 signals received from the antenna 96 from the earth station 8 are redirected to one of the beams of the antenna 90 according to the frequency band in which the signals are transmitted from the earth station 8.
For the sake of clarity, a single antenna 90 2o and beam-forming device 92 are shown. However, since different carrier frequencies are used for the forward and return links, separate receiving and transmitting antennas 90 and beam-forming devices 92 will W~ 96/0381~t P<.'TlGB9510I103 preferab? y be used.
SiG~I~,LIf~NC FOFt,T~~,T
As shown in Figur a ~ , the ear ~ h s ration 8 can coa~unicate grit h a number of :aobile ~er~ainals ~ 3 at tze same tree :av sending packets ~, to ~ secauen~ia? ~.v in a repeat~.ng time frane F, the beginning of ;~hich is harked by a frame header signal. Each frane : is civided into a nu~°a:oer of time slots tl to t, core esponding ro dif r er en t channe:~s , each channe'_ 1.0 being assigned to one of the :ao~a.~8~ terninais L8 by t.:he earth s;.ation o~ ~rhen a ca?"1. is set uD.
Fcr exam~a',e, if tem mcbi:~.e te.rmina? 18 has- beer.
assigned to the f i~ s t c:~a~:ne; , i t wi? decode only the aacke t ~t in t::e f it s t s is t t; in each fr ane :' to generate a voice signa? A The ~aetloc of m~a'.:~~,p.~exed cQ~un.~e,.~~~.a.,6~~a r.~ kn~~~Z ~J ~.~'a.'n~e ~...~~.rreo, e~a..~ ~b:~ 1~.
r~c~e5a, C~~' ~~~~S.a A channe, is assigned to eac~~ ~:::oile ter~t~.nal 18 d~.aring c~a? ~ setup b~ t~ransA~..~r~:a.~~~ an instruction ~~~'~.~1~~. FC:C"~ ~~iE=' 1Y3C~~33,.~..~': "~E:a'~ ',"~'..°.2~~. 7. "., a i.~ Om ~ ~: E:a'?'~'~"'1.
~h Fa~=~. n~ob~.?ae t.r~~~aR...~a~:l. ~~3 ~.s ~.~~~ic~nec~ a x°et~:~rxv ~a~a~~xm~. hava:~~c~ . ~a~wc~.~jc E~~~,~.ne~l ~~.xr~.e ~j'~.ot t, rLi,ffe:~~~n~~
~~°r~~~ :pat c~a ~p~~ .f c~r~~a~~~~x c»:ra~nP~. ; j x:. the fr aye ~°3, ~c x ~5 ~rans~tti.as~.c~n r.~f a. ret~t~rb~ p~.cl~et '~'~ ~:.~~ '.~'~,. Fc~~~
ea~a~~~~:l.e, r the ~aa~~.~.~.e te~x~~~.;~a~. ~..8 ~.c~ s~h~.c~z t.k~.e ~~'irst. s'~ o~~ tt is '6V0 96103814 P(.'TlGB95101I03 _ ~7 assigned °ar reception of the packet R; may be assigned the thir sl of ~ for the trans~nisson of a retux-:~
! packet T, Different freguencies fa and f. are used far the for~~ard and return channels so that the mobile a ter mina? s I3 cem~unica to irz f,sll duo? ex mode.
Al tarnativel v, a ha? f dup? ex mcde coi? c: be used, in whic:~ the re=ur:: pack~ts 'I" woulc: be t=ansm~.tted at c t:~e same =~ ecuercv as the f or°~rar d packe ~.s ~, with the fi f o~ ~rard packets ~ a'_ trr na ring w i th to r star n packets a T in the ~r ame ~° .
Eac~ for~~~.~~d and evur~: ~sac~kev rc~n silts of a hedCle.'..' uo~ .'~.,.,,_~T~e ~ ''t c:~rl to 5;.b~'~~~1 .C"~
~~~3i...°v.a~ :.AI~ OAS at~on, speecz data 26 arbd a check p~r tio~ Z8 such as a CRC
f or cor= ec t~.ng err ors in the speecz ca to 2 6 .
~5 In cr~e°~ ~.o ensure that the cV~aecr signal is a n~e~, v~r~ ~~i ~'c°~~'~ 'b~7~'1~~~~' G:~ a:'~21,~c't.?. ~ 8 , ~~'1 ~h~ s~:~~ ~~~a~
s~.c~t t ~,a~ eve.~~. fra~~ y", L.~~e twa~~vh sea4~.mc~n 8 de3ays the t;.~n~ caf teans~3~~s~.o~ ~~~t~3 thp ~u~~~r~ X35 tc~ a par tic,uJ.,a~' sate~~~.te tU cc~mpens~.te :;cad th~ va~~at~,.rans ~y a-.
~:A~F~. ~'t~k7~~z'~,7T.~.~'>:~ ~~3 ~f ~~,~" ~c~:~'.'~~1. S~;ca v ~...Lak~ ~
~~,~ ~..X~~,~.L~t~~' b... ~ ..~ E« ~ t ~.~c?~'~ t~~i~.t ~~,~~~'~~X2~~a~a~x'~~.~. J,c~~~ r~~. ;~~~ K3~~~ ;;.S,o~3~
~' d." Gyye '6°' q y,~ d..
,.he d~~z.~,~<..ent, sa~el.y...i~~.e,s so that ~~~e<,..~ ~ao~;~~~~.~an, axed.
r ange may be ca? cu~.a,tec~ at a~~y :ins ~a~:6=, Ire ac~di.ti~arb ~
3a CA 02432347 2003-06-27 P(.'TIGB951D1103 ' ~O 96103814 _ I3 .
the position of each mobile terminal I8 is det~rmined.
This may be ach ~eved by cor~par ing the deI ays in the signals 3a, 3b transmit~ed fron. the mobile termina? L8 by different sate.? ices 4a, 4b. F:octever, ~'~is method requir es that the signal s 3 are r ecei.ved fr om more than one satellite if an una:abiguous measurement is to be achieved. Because ov blocaage, this :gay not be :w PCSS.'mble. 1"'.enC°,, ad,.rq....~.~~vna~ ~~s~.'~.ol°i s.eeLer::L~.:i~~,.nCj methcds should be used.
3s eac:~ sated l ite 4a, 4b genera'es an array of beams at dif f er en t. a~C~~..es, the ~.ncc:? az° posi ~.ior~ of the mobile te~°:~a~.na~ h8 rel alive ~~ a sate? q to is deLer~~.iled b~ l.den ~..~~.~;~1.i1~' tile L.~~~~ T ~~. Loh~C~: tfe r °
~L~n signal 3 is detected. Tn adGa.it~.Cn, th°_ ~C_L'~ler Sh~f t of the signal 3 is :neasured to det~ane thQ angl a of the mobil.~ ter~i.:~a.':. 9s8 re~a~.a.w~ ~.~ the ~.~~=_.~°ew°;~~,~r~~~ of :~o~i~~ o~ ~:~~~ Sa~~.?'~.1. i.r~ ~ Tie ~~~~ h~'~~.~.~;J1°i ~9::i~?~c~~~ W Jbwi,.~:e tesi~9~:~a1 I~ ys calc~w~..a~~~9ci. by soi~~: o~° al.~j. cap the a.:oo~e tec:~ni~ues .
~9h ~ a ~.~:' v..o ~"~ S t, c~ l . ~,. ~2 %'t Ei ~i.lS. -~ '"'..~,° ~ ~
~3. C~ ,.: ~ ~.°.°". 1Z.''~ t a ~°~
~Jf~'_~~''.er. '.~i~~ ~~ c~!:~~,G.'S1. I'7Clp ~:..3.~ ~._°"~:'::.,~:
~.~1.<°~ 1. ~.i ~, :~aC~ t.~l.~'f, 'u=~. ~.~:..L~~fA
°.a'6.,~.~.:a.~~:~..~.A...1.~..JXi .~i.~E?:1~. ~5,5~''~,%~.7~:
~.~t..>,.~~..:~:~G~.°. i.7~.~..,.~.. ~..:.:.: i:;'.,~Lt'«-,..
J~S~:J~'7,.~.:~.~~:
~.~"' ..L'i.,.',rAC'k~ .~,.~ .~.~ t~~;~~'.~, T.(~t~S"~~~ 3..~'l i."i'_'.~
'w5~""~~V'a.i;3L~'~: ~?.':'~'xi, <, ~ ~llCl~.~a. ~.4; 6..~~';'~?7, t'Y.c~~"'...r-- ~ r ,e3..j ~ ~~~. a~io. 1~..~.. W ,<. ~ , ~ ~ ~..ej, l ~ :~hC>.~~.~c~~. ~~~:,Ca~a~9. T. ~~;9::~ j. i..:l:,t'~j~t..!~Li~eX Za~ha~, e-'z't f 4>~'~ ~ ~Xc?:~~'t_~.E~c~~: ~.''. ~r dete~,'miR~~~ng' ~:~le Laos ~.~v.~.C~x~ Caf ti2~ ~zxc~k~:~.l.~'.
'~.',ex~~~~.Y~a~ ~ E~ a ° WO 9610381~t CA 02432347 2003-06-27 ~~l~aB95~d~1d3 which information may be incorporated in signals tr ans:ni t tad to the ear th sta tion 8 .
The timing of transmission of the return rackets T is sync hronized by the mobil a term~.aa? 18 with the S timing of the reception of the fay.~ard pac.~Cets R.
I
Since the ea=-th s to tion 8 cont,r ols the timir.~g at which the for-~raed packe~s I2 are received, the ~~.my~g of t:Ze i mobil a terwna= I8 is controlled by t:~e eary~h station 8 . Ta allow some :aar c~i.n f or ~°~.iming er r cr , t:'~e t=m:e slots are separa~ed by short ir°dtervals, called "guard hands".
ur t:~e~ore, the conty o l l er 88 of the earn '.h station a meas~z~es the I~~n~l er sh if ~, of the s~.cnal 3 received tram each mobile terminal and cont:-ols ~:.~:e 1~ mcdulation _re~.tency of the R. mcdula;.ors 80' to c.'°7$IleIi~a~.~ ~Oi i»i3.°~. ~C7~'~.~.el" sl~'1..,°.t' so .~.~3a~ '~h~ ~1~C"re'nu~.~:.
1 ~aa is a ~ ways e~ ec:e~.ved b~ t:°~e rtob ~ol~ te~,.na.i,. ~,F~ a V.
the assigned f~°ea~uez~cvm ~y the shave comt~ensatory technigues , which ar a card ied out a t t:ze earth s ~.at~.on 2~ 8 , the pr o~;.essi ~c~~ burc~ee~ cax~ the mobwi.,I~ te~..~ae.l s :~8 ~i~s z;er~cac~~c~ s~~ ~4~Z~,,. ~~~eSr.:~ ~~3~.~.«.b~.~.~.ty ~za~~ be x~r~ckY~a~:~d, ~;~e >~ C~~'~I~W ..,-~e~ .~~..z..,5'Y. I~~'~' ~',J~ ~te~~~ ~~c~d't'fJisx_..~~7 ~..,~i.I~S~..a_~_~"~.~C~ i°4I'~f~.
~;''~'e~ J.~'s'~~' ~~ TC~'s~I~ftf~<~.~~",;~"~:,'.i~. s~.~:, ~..~7~
CmC.~~%°~m ~~~a~e u,."aa~°X e~~~~ s~.~.e.'r,li.~e may be ~~~.ectec~. c~-~: ~~j~.
f'e~~~ra~=d, ~.~.n.,~, ~:~~e sz.g~~.:l. I ~ ~.:roztt t~~e. ~a~~~a~. ~v~.c:
~,ca~~v 8 be~.z~c~ txa~.sm~.~~~~-:d tea each. selectec.~ s~ ~~~~al ~ioew. ~raa;~~.,~~~, ' WO 96103814 ~ 02432347 2003-06-27 PCTIG895l01103 timing calculated so that the signals 15a; 15b from the sate? lites 4a, 4b arr ive siatul taneousl y at the mobile ternina 1 13 .
B ~r~M ARRANN G ..~':~1'r' -5 Each satell~.te 4a, 4b has an array' antenna 90, f or comnunica tian :with the mcbi l a te~in<~1 1 ~ , whic:°I
synthesizes a number of over l appi:.g spot beams each having a pr o ~ ec to d ar ea ~ 0 on the each' s sur f ace cf bet~aeer. 1000km and 3000k:n in diame_er , as shown in 10 Figure 7. Tn : igt:re 7, the nadir of 'he satel lite 4a on the ea~h's surface 9.s sa'1~Wn ds. ~l'5~,n'~ ~ and tale nadir cf the satellite 4:~~ is shc~~rn a~ poi.n~ B, °ath the great cir°°le d; stance be:::,reen these poi:.ts being d 1 reoresentad by the horizonta_ axis. '="~e vertmcal axis 1.~ represents dis t.ance a? ong a gr ea t cir c.le orthcgonal to ~'~e great c ivcl a c~onxa.~~~<:n~.ng ~:he na H~.~°s o~ the t~rc sat~:l~ 1 ~..~e~ 4c'~; 4b a ~~,~ 1~-~c')~~x.~" :~ '~.~~'~~,.:~~?. Z..~~ ~..~
~C?c~"'~.~~'.
~~i th~.n. the fc~ot~~vrt .~c~ of one: s~~t bead;;. of the satellite 4a and P~~.thi.z~ the foot'orint SI. o= a soot C 0 bead66 ~~ ~i~e J4~~e-i.?..vi... .1~.~ ~~9', :a~.i ~e~.~,l~s.
~.a~~u~~.cv.~..~i~,.e.~w,~~ .~s KIC~s~' ~)_~:.~; ''v('i.c'~ F'~ j~'~::~'l~5'- ice, v..~-''..~ L
'L. ~C~ C~ .
~::It°,h ~.?~'..Ywr~'t' d.,r1''.~!t'~.1:?rl ~(a iat9u~d' ~~"O~j-C..-''C:."A" ~~.:~ ~,7~.'~I~s Gm~~",~.,a.°'~°'~,_°"'~!'~~.~y ~~'C:y'~"'"Ee.'°?";.x.:rk~.j ~~;t_3k)~Si.a1'ls:.~,a~ ~..ij ~~.~~'-~
~%~.k_..~.:.~, f.~.'P~~C:R.
~':i~~E'~~ ~.~G:CUNS
~o-.S ~hQWn ~L..KI ~~_gq~,~~~~ ~, 1..S3e G~~L~t'~ ~f ~h~ ~~~.~~'s ' WO 96/03814 ~ 02432347 2003-06-27 pCTIGB95lO1I03 , surzace is divided by the controller 88 into regions 52 and a sub-carrier transmission and reception frectuenc~ pair is assigned to each region 5Z. Thus, the transmit and receive frecuency for each mobile I
terminal ~8 ara determined according to the: regian 52 in which it is located, the regions 52 being fixed relative to the ear 'h's surface. 5 sample spot beam f ootprin t 5 o is s::cwn over lagp:.ng a gv cup of rec_ons 52, which are hexagonal in this exa:~pme.
to When a cal ? is set up, the pos i°ior. of the mebi le tarm.nal Z8 is dete~i,ned by the co;bt.~°s~? lnr 88 of the ear th s ration ~o acccr ddn~ to the tec h::icues descr'_bed grove and a ccr. tr o? sicna l .s tr ansmi t red to the mobile te~ina:. ~8 to assign a pa= ;.icul ar pair of freguencies. These freguencies remain unchanged tr rotz~;i~ou~~ the call unE.~~ess ':.r :uc:~~ve ~.e~.~~,.ina~ ~
Multi-Beam TDt~A Satellite Mooile Communications System T~C:~NICAL ~'°:L~
The rresent inveraticn r a l a tes to a ~et.hcd and acbara tus ~ or counica tron via sa to l l i to , and ~n particulad but nct exclusively m ~ voice oy data communication using non-geostotdcna~T sate~lites and/ or ~ob~le te~~.nal s .
B ~ CKGROU~ID ? R'~'°
In eomaunica tion sys ~.e~s ~iz~.c h use non IO geostationaa~, satea~ i.tes, the nu~.:e~ and crie:°~tat~on o~: satell~'es ~n vi,e.~r c~ a ga cund~°based tei:~a1 va~°ies dug ~ng a ca 1 ~. a I'ls.~.s , the eu~.:,°~unicoa t~cn lmnk between the ~e~~':a.e ~,~ed a.:y CSne s c..'~''~~~~ 'Wa '.flay a~eeCCu'Ze weakev as the e~evatien angle cd the sate~L~~a decmeases and u~.t~.~a te~.v t..he ~~.r~c ~~ay be;~c~e .'..Ild'~eT~~a~~ a as t:'~~ sc°1~~1_!~ :>~c i~C.~'sl~~ .'",~1~~~.
C,?° ~ ~~,.'e°'2.'w C7° ~u"~' L ~ ~":i31. '~"! ~ ~ ~ ~ ~, a ~ "v.»?. ~~m ~, ,m. ~ ~~ ~ d y s~.~e :~ v, ~. ~
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a~'l~lth~?° s~ 'e~, T 1~ ee ~CJ~ r;:'°Ju~m'~.C~~ ~ ~ f'sT~
4F:~"~~;
te''.~lons~.s? , ~:I a ~"°. ~~eC~Lb~~~°'- ~n~wn as °t}'lC~ndwe~ ~$ o 'the c~~ ~;~;c°va~~~~~ ~~ ~~~_,_~ ~ ~ ~ x y~ cad ~.~s,~~~ ibex ::at~~~
su.ra.~ ~~~::.~~.rd _ _< . a ~e,rll; , ~iC~z,fi'~'ii~'~ , h~.nS~G~~f(.~,,~ ~~~':.,t~'s~~:~,Z'!
~~~''.c.?_1,7,9.d..~:s'~i bi~%~a'V' 1. . a ~_,C7t:,~'~ C'a~ ~~~ ~ C~~: is~~~~ ~ k_C~a~~ ~.,, UG' ~t .9.Cn~'.'~ "~~~;~.'~
~~'~:" CJY?
r b w~ ~.., ~ a " ~'~ z~ ~ : ~~ 7 Y":yf ~ C 't, ~~ ~ ~7 ~' r: ~yn~. ~. g~.t a e:. i ~ ~ ; ~d ~ ~, ~,~ a.,. rt.. ~:z.s~.~.~ ~ a r C~~~~, ~".C~i~.~i~..?.~e~.C~'~ ~..~.C'jk~ a .k_ ~ 'S 9 - ..~'...' C 9. ~ ~ y ~ e.~, ~.H ~g l.,. ~ ~'; ~"'.>.r, e. ~.A~ 4~.
~5 ~; x~~~a~e~:~~r~r.H,., the ~_~~v~, ea.~
t., ~=.e~:~ia~ial az~d a ~a:~°tize~~~ a~° s~.~_~.~? ~.:~.r~~ ~.~aza ~~~~~o ' ' WO 96!03814 ~ 02432347 2003-06-27 pCTIGB95l0I I03 ' 2 obstruc~ed by buildings, trees Qr other obs;.aci es as '., a the terminal er the sate!! i to :coves during a call.
This ef=ec~ is known as "blockage°', and reads to i fading =n the received signal.
Sicnal fading may also occur when a signal transmitted by a satellite is ref? ec-ed off the grcund a or bui' d;ngs and th a ref lee red s ~.grar is received at the te~~.nal tcge they w~eth °he dir p : r s bgnal . The chase d if er ence between the d~.rec= and :: ef leered IO s ignal s may lead to des trucrive ~.r~ :.er f erence a c the '~,.=_r'~i~Ya' , sG~ t~3c~ w. '~,~~~ z '.'~,:e T~.ve~, s.>.cnam S tr eng'h iS
d reduced. This is ~~~c~w~~ as °':~~.i ~.~~.,~~H~° fadi.~.~.
The ~C.'c'~a'°°le:lt ~1(~°°~...C~~ ~4;>i'd ~m.s'~.',~.;...~e°aG'~:a a ~as.e;.~'~,d.e ' communica tion svs te:n in which th a sa ~eil.ites zaonitor the cua~it°: of si.gria~, ~°ece~.ved r~:c;~ a tpina' and determine wh°.cJ' c~~ie ~5 ~~es~ sr~i~.uc:~, ;~; han~,~.e she ca~.:~
~:o the ~e~.:~~a? ., care ref the say a ~" ~ ~. ;yes w~e.,.~~ azami is , the signal recei°~red f.~ em the ~:e.°.inah ~o ~ther satellites or gateways. i 2 Q 'the conf er enc~~3 ~a~er reThe C~~~9c~ba 1 s ta~° ~'obi~ a ~at~.~:.~..~.be ~~,~i'~~C~~. L°5~~2,~ ~~c:"'~.GX''al.C~~ ~e<"~GI"~~..1 ~~~lunq.c~~°.~.~.7~~"' ~~ ~il~.~~',~~~,:sb~P7. a1'x~=- ~J,.~..e~~l,y ~rt%
~.~°l~e~'1'~.~~1 ~~Ae'~~. ~~,JS'~~?:,.~:.E~
,~,i~'~°~..1.~:..~,.~P t.:~a~as.t.'-T~'r.~~.~lt~:~!' ~Li"°a_~
Jlln~
~, ~~s~C~e~l~, ~'c~,~..~,.a.,~?~'?~i.l.~ C~9.,s~~.~~:i~-a~ r'~
i..:C'~~t,~~i23.~~tt~~.~"~
~ys te~~s3 ~,n Zsi~, ~.~~'I ~~.'''~~~~:i~ ~",.:t.:'~,..SS;. ~.~.~?1~;. ~.e i?.:L,'f b.°e:°~'.1.~E?.'~ ~~' two or three sate~...lates; e~atec~a~% ~E.:~;p.~a~~s me2~su~°e tY~
CVO 96103814 PCTIG$9510I103 ' 3 signal lever e. each of these alternate paths and control which s~r~'~.al paths are used. This systen is exclusively desicned for use wi~h code-divided nultiple access (COMA).
However , COMA suf f ers fr ors a nu,~::er of dr awbacrs when used for mcbile com.~°nunica~.~.ors. The nobile terminal s are complex, since they rec~~ire a separate decoder for eacsatel life path. :~c:~°eover , COl~.x~ is inefficient in =recuency re-use unless the users are IO evenly dsstd ibuted, and p~~rer level s canno;~ be 4r eel y varied for each user witk~o~:~t ca.us:.~yac~ ~.nter'erea~ce for other user s . : u~ ~~xeor~ s a.~~u ~ ør ~.ca~ ~ i:ate~ f pr ence takes gal ace at cea:~c level s of use c~r~'r '~'~t'ti::~T'T_' 0 ~ '~'~° =° ~'_W~':~t'~'TOId S ~.cc: rd~.ng ~c one aspect of the p.°esen~. i.~:veo".iot2, t~:ere .:.s o~:cvidec~b a me~hr~d r.~f cc~~~;s'a.va~,vc~r~ e~:~eeev a ~°~°~'e~~~:.<'"°..d' s~~':,',.'..C3°1 aTlC:~ a ?J,.L~~"~.S~T.~.~d Ca f' ~:~a.d'1~.~,:'~~~W L'~~,'l.~iC
TDl~ t.r~ address each ~:~ the ~:er~mTxa? s =row t.'~e te~~'e~°~b'~.yd~ sta;:~,~°l, In WtI~.C~"~
d~.~le'"°~3.w.°.~ 3_s pW°~yJ~.~.~'c3. ,~~1 C t~~ ~..~xlk. ~et:de~ri ~h~ to ~'~ ~~ t'," ~.~ ~.. s ~.~'~'. bO22 ~~~C~
~~c$~.
~;.,..3~;"'bS3~,.$$c,~~:, ~9'~ ~~a~C:~"~.~~ t~'~k.~ ;~r.,l~i~:
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fig' ~L(~~ ~ ~~'"~'~b~~r~ w°s ., '~~'t.e' :1-~1.~.~7~~Y~'~:~,~C1 ~~1~.~" ~4~fs. ~i~~'.'.~'~c.'. .~..'%:z w~'1~>~~~3:F9 ~;'~~~.~f~ ~"'.P..~~
x . ~ ~-, s s~~ cat. ~.h~~u~h ; ;-ee ~.w~ cap; ~co~'e sa~~c~~.~ ....~~s, ~;~ Aaav be ~~e~.~u ~.xr c~~~,f~e~ea~~; ~.:~~~:~ WI:~~~a:.~ .
In this way, blockage may tae a ~~,uced w b~:h~s~ the CA 02432347 2003-06-27 ' 6V0 96103814 ~C'TIGB95101I03 a inherent disadvantages of CDMA.
The terrestrial station may either deccde the bes t received signal fr ~ra each te~~..~.al or zaay combi ne all cf the received signals to reduce err:;r in the received s ignal . The ter r es ti is l s 'a'tien may then select a fa~~~rard 1 ink tc each terminal t~'~rough one er more of the sate? l ites according ~o t~e ~xali.y of signal rec~ived frcz~ the term'_nal thrrugh the satel li tes .
0 Thus, a smooth handcver ~zay be ach~eved and blockage a~~ri fading zzzay be r ~d~z.c~e~'~.
4.n o~'der t~~a~.. ~l~e 5~.:mea~»~ia~ ~.n ~~t~?'..ate fvr the f0~"~Ir'3~'d .~'..'sl~C: :~a~y be tJ:~Ils~:Ja.:"°~b~ t;: r:ee t=
~°r.na~, the ter r es tr ial s to tion znay calcul a to the delay i:, the l~ td az~s~'.~ss ~c~~ ~~a the sel ec t..ed sate~.~..~:.e and ady;s t the sage ~:~,me s~.ot th~cug~~c~ut the cal' . The c~.l c~.~l atic~n may ta~.e in~c~ accc~.znt ~acth the va:~ia.ticz~ iz~ de~oay as the ;-~~.~. '~C'v'C:~!'~ ~'ac ~'.~.7..~.~.'~'.r~.~ i~.c,'~'~1~ a ~~' 1.r!.;~:s.Vr~ C:, CI ',al.E? ~q~~L ~8 c'~.dl~. ''~,'.i'~C, t~~.E.~°:!'°d~'1G~:~ .~~°l, t;~i~',LcA~%' ~.~~-~E'T"S ~rt:'~C~.~,oxr-°~'' ~t'y'~,~ ~',y4~~i C'~~~~e i .. lw, ~ .,~ ,.~ :.. :. L.~, ~ ~ R
~~5'~~~Y~°..~e.~~~l>C9t'i ~~~~ C~i~s': l~ik3~~r~~.:~°r~.i;~.
a~~, ~~i~C~i'~.cx~f~m~~" ~'~1'~C~ C~:~:~~L~x.~:k ~.3.~G~L~.~~'~'~~' r'.~ tbt~~~'. Ym~.~L~,..l:'~~~. Y_~r. ~:~'J:C:
yr:,~~j,~~RxG)..~.:, .~.Z'j. 'e~'C~,~X.~.ig.'s;C~it;, ~'~°1~.~,~am'v°'~,'~xr~r..:'~<..;.. ~ri~',~~:d>C:)~E his.
c~a~~en~a~:e fC~~'' the ~C~~a~:~eY° si.ia~~-~. ~..~'~ tk~.~: sig-rxa?..
w~ 96~~38~~ CA 02432347 2003-06-27 pC.Iy~gg~dI103 ' S
received from the terminal and adjust ~he freguency of the trans:aitted signal accordingly so that the terminal r eceives a s ~gna~. a ~. a constant fr ecruencv tl'zroughout a cal=. The Dcpgler shit t may be pa= tial ly cnmoensated for by the satellites.
According to another aspect ef the present inven Lion, in order to f ac=1 i to t= s=mul taneous communication wath multipla users through one sate? lite, ar eas of the earth ar a divided into a number of fixes regions, with , a arecuency being assigned to a ~er:~~ ~,al bath for ~.m ans~ission and recept~son of sicnals ac::ord.i..ng ~.o the :.°egior.: in wr~.ch the ter~nmnal is 1 coated . The 1 ocati~~.s of the a rc ions are deterained ac:.ording to their positions on the earth, rather: thar', thei~ g~~sit.ions ~eiati~re 'o the sae? 1_ite> ~mmu? ~.araeous coud ~..crt.ion between d.~fe~'~.~z~~, ~.- ~ra~,.~z~.~.s ~.~ the sazz~.e rec'~..c~~: ~.r~d a;~: th4a same f r er~ueg~~s.~ es ~~ay ~~e a~~~ 2.,evec~ b~' al? race tinc~~ d~.f f e4 ~~a~
t.
t~me slots wit.:~mn a repeating time frame to each of ZQ t~s3e 4 ~""C~b:,,~.nl~~.'"~ , ~.~":r'~C>'fw ~' ~r~~ ~' ~"~'~'re~ i_ ~."=.m"~°."~.~~"R~~1.~ a~~~~'b~9 °~, ~~~fg~. ~''':!,'~t~~~P~~aY',t:.. ~ F3:a ~K.','E,.-'' ~:~P~.~~
.d'3eCi r~ .. ~.~3.~.'l. 'G"' '. ~ :St;~C
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k:~%'YGm~:)CJ. ~ ,aY~.~.'~'t .P".xl~ ~r,"',.Y ~.~~~.RV
t.~~e s lobs aura ~.~ied 2 ~ ~c~~:~'9~'r~.~.%lg ~ ~a c'~~I~3h~X '-~~~° aS6~t~~ ~". C~ °.' '~_'t~~" 'r_.'rwn~~:~~"~ 's~
irz~°entir~r~y thex~~: is px°ca~ri..de~c~. a et':~.~:aoaf ~~a~~~.~~a~ ~.a..r~r~
\.
WO 9610381.1 PCTIGB95/01103 a a nen-ge~stationary satellite which generates a plurality of individually steerable beams to provide communica Liens ? in)cs , in which each beam is dir ec Led towar ds a f fixed r egion a r the err th' s suv ace un til the beam is no longer sui table f or co,:~un_cation caith that 'fixed region as a resist o~ the 'prcc;ress of the sa to l l i to r a l a t=ve to the ear th' s sur _-'ace . ~':~e beam is then red~.r ec°ed to a rew f zxe~' r ecion with which saris°actorr comaunicaticn is possible. Calls to the pr'nv~ous ~ fixed region may be r oared t~.r cugh another satellite.
~r. 'h~.s Way; the =~°egue.:~cv o~ beam-to~pbeam handcver may be r edF~.ced, w i t:~ou t a.~ ec t:.a~~ the f regt.:ercy o 'f sate l ? i re-to-sa to l l i re h andover .
L5 '~'"he presen t ma~ven'~.ion ex wens to a :.er= es ~..r is 1 sta~.can having means ~.o~. per°o.~.n~ ;.he ~a:°lcc~.ons o:~.
yw ..~. ~ .~ mo b s,. .~... y r ~ 5 ~ ~ r descr ibed aho~re .
BFW~'= DB'SC~I'~'~''1°QT\t ~~° mxr~; D~.~WTN~S
Specg.L~=_c' e~~_t~~c~.~ei:~~-.s o~: '~.he p:~eser.t inve~ation w.i.J~~~ P~c~~~ ~~; c~~ c::~.:~~:;e.~. w~..~°~~.tv~ :~r~r~=ar~~c~~:
t;:~ ~i:,.t~e, ~~ca~"ai3~Ji$Il~d.k~~ t~~;°t~it~~~..T-iC~ S , ~~ '4~}i~;.~..~ _ '°
~'~.:~1"Lt°°~. ~. ~.~ ~4:~~. ~LE':uiw~:~,.~;. ~"3 i x"7t~'~
d~a~'~,xt1 C.7 ~° Cs~'~.e f'c~'~ra~~d a~~~ r~:~:.u~.°xa :~.:~~v~~,A ~,e'',~°~reez <:~.~, earth. s~ata,c~~~ ~.x~d.
2S a mcb~~le ~:e~:~~.:~_x~~,~
~'i.r~tzr~~ ? ~..s ~, se°.~'~e.ma,t ~.c e:~e.va'~i~aa sty;~~r~.z~~~
'' 7 a?ternative paths between the earvh station and the aobile terminal;
F iguy~e 3 is a schematic diacra:~ er the ea~~h s ration;
Figure 4 is a schematic diagram. a~ the mobile terminal;
F igur a :, is a schema tic diagr a:~ c. one of the sateii ites;
Figure 5 is a diagram cf the vorwat o~ ~or-,~ard 1~ and return packs t.s Within a ~r a:ae actor ding to a g:.r s t embodiment;
W~.. a ~ slwows the ar r av~e~eii w - 01 s~~i v be.arji ~~'Cr..'7r?n's oI1 the ~a?~~.hy~ sur~aCe, d 1C~= ° 3 shoWS the ai ~ anCe:3en ~ o '.~, ce 1 ~ S on tile earth's su.~.~°~ace i b the ~irs~~ embed~me::v;
~~"c~wo ~ ~h~~~ h~~J v.h~ ~~~'~s tei°° ~ Sc~~et, ~'a a~e dm~°ec red in tae ~ ~.r sv em~:r~di~en t as t he sa tee? R ~. to pd°o~resses in its o~-b~~.~~;
r ig~.r a 1.0 is a d~.agr am of the ~or~.at of ~o~ ~rarc~
~ 0 ~ . ~' ' < ~ ~. *.
i.-~~~C°~. x"~' (.~.1~'.a1 ~at~"K~ i~:~ ';J ~ ~ St..:?.~1 c'~-. '~:
s4°~E': G'i(~ ~ ~ .'~',.;1~ ~'.J a ~~t'_°.o."".7~'~C~ f~~i;~t'~C~i3 v~ic°Hkt,r~-p s'~.~'SC~.
d s2. ~,~ a C~..~.s~~~~ 2l'!:i~ fix: c~11 ~._~_'~,~~'bl~~..L'ti~ a~r~Ilaw.
~~~.~ ~ ~~a.~° ~-~aao~x~ a,.~a. r' ~.c~~~re ~(~,DES FOR CARRYING OUT THE INVENTION
FIRST ,~1~BODIM~
. A first embodiment of the present invention will now be described ;pith reference to Figures = to 8.
In Figure 1, a terminal 2 of a mobile terminal transmiis a signal 3. The mobile terminal has a '~ substantially omni-directional antenna, so that the transmit~ed signal 3 is received by a first satellite ~4a and a second satellite 4b in' view of tze mobile 10~ 'terminal. The signal 3 is retransmitted =rpm each satellite 4a, 4b as separate signals 3a and 3a. These signals 3a and 3b are received by an earth station 8 ' having first and second receivers sa and sb far receiving signals from the fist and seccnd satellites 4a and 4b respectively. ~ In this embodiment, .-..'~e eart.'~
station 8 has first and second directional antennas directed towards the first and second satel_ites 4a, 4b respectively. Thus, the same information is received~twice by the earth station 8 in the separate ' 20 signals 3a and 3b. The earth station 8 may :herefore select the better of the two signals 3a and 3b, s.g.
' the one with the lowest error rate, for conversion to ' an analog signal for transmission over a public service telephone network (PSTN) 9. Alternatively, if both signals contain errors, data may be derived from both signals to provide a combined signal with fewer or no errors. The combined signal is then analog converted and sent to the PSTN 9.
The earth station 8 also analyses the received signals 3a and 3b to determine which is of better quality. Since there is a strong correlation between the streng',.h o! a return link from oae of the satellites 4a, 4b and the strength of a farwg:d link to the portable terminal 2 through the same satellite 4a:., 4b, ~e earth station a selects ane of the satellites~a~ 4b, for the forward link to the portable terminal 2 and generates a selection signal 10.
When a signal is received from the PSTN 9 far transmissicn to the portable terminal 2, the signal is IS passed to a transmitter 12 in the earth station. Ths transmitter 12 selects one of the satellites 4a, 4b, as shown schematically in Figure 1 by a switch 14, in response to the selection signal 10. In this case, the first satellite 4a is selected as the most suitable for the forward link. The transmitter 12 then transmits a signal 15 to the first satellite 4a, which retransmits the signal as~ a signal 15a to .a receiver 16 of the~mobile terminal. The transmitter ~12 and the receiver 16 may be connected to the same 25 antenna vn the mobile terminal, or to separate antennas. In both cases, the receiving antenna is CA 02432347 2003-06-27 p~'/Ggg5101103 WO 96l038I4 Ip omni-directional and therefore may rec~ive signals from either of the satellites 4a, 4b. Thus, the receiver Io receives a signal '_5 t~:~ ough the s tr onger Link.
~ situation in which blockage occsrs will row be described :rith reverence to Figure 2. This figure shcws a sec tion c f the ear th' s sur f ace on which the ear th station 8 and a ~ucabi 1 ~ terminal Ic~ are located.
The =first and secrnd satellites 4a, ~~r are within the IO line of sight of both t::e each s ration 8 and the mobil a te~ina? I~ . The ang?.e of eleva;._on Ey cf the second sate? T,~> to ~°~b r a 1 a rive t o the mofile :.ei:~al is y~eate,r than the angle ~~ elevation ;, of the direr sate?? ire ~a ar.d the ~aath distances be~ween the earth Sta~~On ~ and the S~~Gin~ SaC~~ ~~.~e 4b, a::d ~eC:de~Il tile ~-'~se0'~nc. Ss'a~:..a"~ 'L~,''~.E, ~~~ ~aI,LV~ ~:~~e ul,t~~")? 1 a tsr::..;~.~:a 7., ~ ~ u''1~'.
S ~'3. (.~" ~''~. "..-~, Y ''.':'~A ~..a~ i;.'~> C;~ S ~'~~ ~;7 a ~°
,~e e:1 Mh ~~? ~.;. ?, r S' t s ~iL a w. ~., ~. 4". ~'a.' ~~ ~'~,. s-'3, ~& ~-..
the mobile terminal 1.~ and ea ~h staticn 8.
~OWever , ~ n ~l',.~~s bas2 th a P'atOD~1 a ta~'.~..:2a1 ~.~ ~s ~C? ~os~.~_.~~ane~~, c<~..c~~e t~~ ~,. t:~:~', c~~a~ .~c.:j.p 20 :auc~ ~.~r ~
c'.r'e~~y.
w~'~~..cy'~> ok~va~~9res -~i~a,~ ~ i...x~~~ c~f s..c~rlv ~ t~ bet~reeoA ,~r.e ~e~b~~
te~."':~:!..5~4'~~. J~~ c'~.~~~ i~.:':3 a ~a.:"..~OneX SasKF:_~-. ~,Je t~' 4b > '~~~lg~'r fd.~~,~"~1 ~hEn ''l~~~~_.~,~~ '(:;F.n.;ii$~.TI "s."f .~.ca '~"'4.~"ct.n<is's~,.~>g;;~ S.
sl~g~G,.,'_. ~ ; 'k',';e,'f~l , Y. ,..
s~.g~2~>~ .~ ~~; c~xi~.y ~r~: ~.:k:l..y ~°~ar°.~~~~~'ed by a-~.e. ~~cw~~:~xr~.
sac:e? 1 ire ~~.~ a.xW vtx~as t~~e ~~pt~~azv~mitred s ~.~<zx~~>1.. ~b ~.s ~iox~e 1 ikel~9 'tc ccr~rain e~:~r ox s . 'the ear ;:.b:~ ~ra~.~:~ox?
a a CA 02432347 2003-06-27 p~j°I~gggI01I03 'OVO 96/03814 selects the firs' satellite 4a as providing a better f or~rard ? ink and tr ans3i is the response signal 1S on? y to the first satell ite 4a. 'his response signa'_ is retransmitted as siCnal ISa to the mobil a terminal I8.
Since the l ine o~ sight la between, the first sated? ite 4a and t a mobil a te~ina? 13 is not ObSC'.LT"'eCi, the response sigrai is recnitred strongly bV t.'~e mobila y ~
~_~-a~inal I8. T'he mobile tw~.,~:al I3 does no°,: ne~d to t a se? ect fro:a ~rhich satr? l ito 4a, 4b _.. is to deceive IO t:~e res~ensa signal lSa, since thus is decided at t.'~e A
a earth sta~ion ~ . Sel e~.°~ic~x of th~a satel lit~s Via, 4b is then ed;,m a t~ axle: ar e~ ~ t;~ the :~r~:om 1 w te=~~_na'_ .
s If, cn the c~her 'xan~., the ~~ci..le te~:.nai a t were to move suc:b that the obstac's 20 no longer a.~ Cb~ true tS 'L...~ a , ine O f a'_~rl t 1:7 , th e'4'e t4 a ea.'. Yh S t3 ,:.~Qn ~ may ~"ec~e~'V'~ a be t ~~~'° S~. ~ z3~~. .~.~ c~~ tLle Sec"~~a°~C~
Sc'~."~e~ ~..~'.°e ~r'~ ~~"3d 6~.''a..:..~> ~s:..~l.~:3:'~'~O"F'E?
.ms's-"'~.-~.~.''O'~ t.~'Ie S~CW:~T"iCC~
satellite 4b for the fcr°~arc~ li.x~.k.
When dif f er en t f rectzencies ad a used f or t.~'Ze ~Ct fc~~;Araw a~ic~ x:a~_~:~.s~ ~~.xv.~~~::,the fa~:~ingis due as:r:, t6~
:~,d:~.~ '~..~.T~~.~-n~ l.n~~~. . t..!' ~s~'13L~~~., C.S ~ (..~'CJ
'~..''.~~I",.~ ~ '~".~'~:'=r"~:! ~ .(~. ~~~' ~4.~~;e~"~~~,~.i.,C~i~ 'Y7~'.~'';~.YE~'~,~,:Cs~a~ t:T:Zd~Ida.~~~~
i~.a:.~' 4:i'lI~ I Y u:.'V ~~ ~f'~E.v:<aa,"'~
.~>"~:.s ~ J"n '~~3.~z.~ ~'~~;~. y. i'".kl.c'~~,'.~k~~.?.X~~~.
'~.:_.'c~Y~."y~.?.,~~,.~~.
xz9>Oi~~,.~Af-~ ~.~
ia~x~cr~xa ~: icon to ~~e e~:~~tb. s c~n ~~:l.at~.rg ~_a t~. ~ ~o ~~e ~7 a~~~~ng'L11 C3.4, ~,.~"~F" ~~-'.~~~~~6~.~, ~b~~.
,eY..'~~oE.''~.~~.''~ ~~,y ~.e~.'131~L~,c~t~..
fx~'~:~m the: ear~"~.~:~ s ta'im ~r~~~ the, ea~''~h sta'~:~r~n g . ~f receives a good retsrn Link signal from the first y t satellite ~a but i:.fcraation trans:.liteed by t.'~e acbile :.
termina_ i3 indica~es that fading is occurring an the f or,~ard link, the ear ~:~ s to tior. 3 may then selec t the satellite from which the next best signal is received for the for-~a=d link. In a case where eac:Z satellite -genera tes seer a 1 over ? a~~ ing beams f or communica tion with mobile ta~_nals at dif f er en ~ f= ecuerC~.es , the ear th s~aticn 8 se=acts ins~sac a d~.~faerer.t :~,eam 1Q generated by vhe fimsL satellite.
The o~ae~a~.? on c~f t~~.e me~b~.~,e ~,~;.nal ~.8 and the earth statian 8 w~.:~?. naw be ewa.~ned w:.t.'~ ~e.~erence tO rte' ~.~Z.m.~ SS ~ p t p ~.:~~.a ~ a FAR'I'T~? S'_"~T?'ON
In t~'1~~ eXc.~,'C~.~'., rlna.~.o~ 5~~.'.eCel ~~.Cnc'31 S a=a r ec~~ Tz~~VPC. a ' ~:'7.~ E?~.'.,° ~'.Le. ~:~ ~°:c"iL..j"CI~.
c3 '_.. C'~ t~e ?c'~'~ 9 i ~~' t~'cin~il~~.~d~rr~"~~3 ~C3 ~~~'. ~."ciC9~'~~~~P: ~~r;.~.~R,.~1_,a ~..~ ~.$ .
r'~.S 5s ~5wT1 In Figure r , the anal v~.e s~oeech s~.g:;jal s are dic~T tizad and encoded bar a cadet ~ ~, and the encoded speech is ~Q COf'1~T~.T~.°te~ y:.3'1'°.;~ a ~~'~'°::..~,c ~J.i.
C~~,'~i.'':~"''~o~ PaC~C'etS c'~.~ ~.
z~ul~..~~g~~.exer~d~:.wu~.t~.~,~___e~r:~°~ ~~.
The tr~~es~~.T~ss:~czn ~.F rt~.e ~~~oke~°~ ~~s concmc~~t.l e~x ~p a. .cc~ni~wMo'l~.er ~~ ~~h~~wc'~ s~~.~:,cts ~~tl~.~.~:~ sa~e~.lite ~ i.~: t~~
be used for he f~.°~~.-~a~~.~,v~ ~H~n.k ~-~n ~°.~,~e basis c~~' the e~ual.i~:v~ of s~,e~~-r~.l re~~~:~v~=e~ f~c~m ~a~:~ Eratellite ~ ~
°~:yhe cc~ntr~~~.? er ~3 c~~c~nt r ca? s a se~.ec°yo*° ~ "~ to send each ij ." W~ 96/03814 ~ PCTlGB95lO1I03 i a i~
packet to one of a z~Lurality of buffers 85a, 85b, 85c.
The timi::g of the output o' eac'.~. buffer 85 is contr o l l ed by the contr o 1 l er 8 8 . '~ he packets eutpu t from the buff=r 35a, 85b, 85c are radio freruencv modulated by corr esponding ~y mcdul a~tor s/demodul ators 86a, 86b, 86c, the frequency of :mcculat ion being cantrolyed by the con~roLl er 88. T he ~..~' signay s are mcdul a fed an dif f er en t fr eCLenC'J DanCS Se.~ec"~.e~ by the controller 88 according to a selec'ed beam o~: the sa ue? li to 4 in ~rhic h the s ignais a~ a to be re-transmitted to the mobile te~i.nal ~ o . The %~° s~.gnal s are transw~~ted b~ direc:t~.o~°ea1 ante::nas 87a, 87b Sic wh ich ar r eacs tear ed 'c~ra~ ds a corm espcnd~.ng satellite ~a, ~b, ~c.
~5 . Eac h m'rect~.ona? antenna 8 i a? a:~ =ecerves signals 4.::~nsl:~.'..~° s b.:~m.ail .°miCJ.~~.:.e a a=:w"aL9'..'°aa.! ~ a'.°d°: ra "~.' ~°~~"~.'~bh '~
~.~k ~ri.'~Ia1 trade. d.W'."..r~;,':.Cee'~cn:;..n~ ~i=~'"sn~..W ~~?,.~r'~,., s',r,r ada:.'~~~.e i:~.~~ ~'t~~~'~".1.C5 fd°eque:~cy demodu~.ated ~y the ~" atodu? ators/
demodul atos 8 6 to fog .r ace ~,~e~ rackets a The :~'a~'s..' 7.~'E?~ ~ a~~e~~~ c'~4 E-~ ~11.~" ' ~.'-~t~~cC~ ~-~i i~.<.e x'71) ~a e~"~ ~j °a ~~'A~',~
~ez~~.~wted °.n c~h~.nne~,s by ~:~t;~.e ~~~rd.~.w~xaT,~:~e~'.l~~em~~~.~:~p:~e:~er 8~ and ~~ee~:~ded b~ faze ~o~3.ec. 8~:~, w~li.~:?T=. ~°.r~~:v ;~'! s~~
p~~~f~~~m a ~°:~c~~° c~aec;~i~zg b~ G_.ompa~~.3.~.f~. ~.,a~:y~.e~=~
~~~~g~.~cAc.~ f~c~l~e ~ c~.~ ~. ~f~ ~ a., % ~ ~,~ e.c ;~. q... n Gad ~ ~< ~ ~' ~: ~ ~...,~., Wh ~:,.~ t,' i ~t.,. ~i a;~. ~~ ~': .~.. ~" .5.. ~4. E'.."~'r ~ c ~~-he resu~.tant analog s:~gnals ax°e sex~r v~,' 'she ~'~a'~ 9 oxz different lines.
The earth station 8 need not be connected directly to the PSTN 9. Instead, earth stations are preferably connected to PSTNs and other fixed and mobile networks through a ground network, as described in patent publications nos. GB-A-2293725 and W096/03814.
MOBILE TERMINAL
As shown in Figure 4, each mobile terminal 18 io includes a microphone 60 in which speech is converted into analog signals. The analog signals are converted to digital signals by an A/D converter 62 and the digital signals are encoded to form the packets by a coder 64. The coded packets are RF
i5 modulated by an RF modulator 66 for transmission from an omnidirectional aerial 68.
Signals received through the aerial 68 are RF
demodulated by a demodulator 70 as received packets.
The received packets are then decoded by a packet 2o decoder 72 to form digital speech signals which are converted to analog speech signals by a D/A converter 74. The analog signals are output to a loudspeaker 76 to produce audible speech. The operation of the mobile terminal 18 is controlled by a control unit 25 59, such as a microprocessor and/or DSP device, which is connected to additional conventional handset components such as a key pad (not shown).
SATELLITE
Referring to Figure 5, each satellite 4 includes an antenna 90 and a beam-forming device 92, which may be a radiating array antenna and a large Butler 5 matrix as described in Patent publication No. GB-A
2288913. The beam-forming device 92 converts signals from each element of the array into signals from a plurality of beams and vice versa. Signals received by the antenna 90 from the mobile terminals 18 are io fed via a control unit 94 to an antenna 96 which retransmits the signals towards the earth station in a frequency band corresponding to the beam in which the signals were received. The antenna 96 may be steered towards the earth station 8. Likewise, i5 signals received from the antenna 96 from the earth station 8 are redirected to one of the beams of the antenna 90 according to the frequency band in which the signals are transmitted from the earth station 8.
For the sake of clarity, a single antenna 90 2o and beam-forming device 92 are shown. However, since different carrier frequencies are used for the forward and return links, separate receiving and transmitting antennas 90 and beam-forming devices 92 will W~ 96/0381~t P<.'TlGB9510I103 preferab? y be used.
SiG~I~,LIf~NC FOFt,T~~,T
As shown in Figur a ~ , the ear ~ h s ration 8 can coa~unicate grit h a number of :aobile ~er~ainals ~ 3 at tze same tree :av sending packets ~, to ~ secauen~ia? ~.v in a repeat~.ng time frane F, the beginning of ;~hich is harked by a frame header signal. Each frane : is civided into a nu~°a:oer of time slots tl to t, core esponding ro dif r er en t channe:~s , each channe'_ 1.0 being assigned to one of the :ao~a.~8~ terninais L8 by t.:he earth s;.ation o~ ~rhen a ca?"1. is set uD.
Fcr exam~a',e, if tem mcbi:~.e te.rmina? 18 has- beer.
assigned to the f i~ s t c:~a~:ne; , i t wi? decode only the aacke t ~t in t::e f it s t s is t t; in each fr ane :' to generate a voice signa? A The ~aetloc of m~a'.:~~,p.~exed cQ~un.~e,.~~~.a.,6~~a r.~ kn~~~Z ~J ~.~'a.'n~e ~...~~.rreo, e~a..~ ~b:~ 1~.
r~c~e5a, C~~' ~~~~S.a A channe, is assigned to eac~~ ~:::oile ter~t~.nal 18 d~.aring c~a? ~ setup b~ t~ransA~..~r~:a.~~~ an instruction ~~~'~.~1~~. FC:C"~ ~~iE=' 1Y3C~~33,.~..~': "~E:a'~ ',"~'..°.2~~. 7. "., a i.~ Om ~ ~: E:a'?'~'~"'1.
~h Fa~=~. n~ob~.?ae t.r~~~aR...~a~:l. ~~3 ~.s ~.~~~ic~nec~ a x°et~:~rxv ~a~a~~xm~. hava:~~c~ . ~a~wc~.~jc E~~~,~.ne~l ~~.xr~.e ~j'~.ot t, rLi,ffe:~~~n~~
~~°r~~~ :pat c~a ~p~~ .f c~r~~a~~~~x c»:ra~nP~. ; j x:. the fr aye ~°3, ~c x ~5 ~rans~tti.as~.c~n r.~f a. ret~t~rb~ p~.cl~et '~'~ ~:.~~ '.~'~,. Fc~~~
ea~a~~~~:l.e, r the ~aa~~.~.~.e te~x~~~.;~a~. ~..8 ~.c~ s~h~.c~z t.k~.e ~~'irst. s'~ o~~ tt is '6V0 96103814 P(.'TlGB95101I03 _ ~7 assigned °ar reception of the packet R; may be assigned the thir sl of ~ for the trans~nisson of a retux-:~
! packet T, Different freguencies fa and f. are used far the for~~ard and return channels so that the mobile a ter mina? s I3 cem~unica to irz f,sll duo? ex mode.
Al tarnativel v, a ha? f dup? ex mcde coi? c: be used, in whic:~ the re=ur:: pack~ts 'I" woulc: be t=ansm~.tted at c t:~e same =~ ecuercv as the f or°~rar d packe ~.s ~, with the fi f o~ ~rard packets ~ a'_ trr na ring w i th to r star n packets a T in the ~r ame ~° .
Eac~ for~~~.~~d and evur~: ~sac~kev rc~n silts of a hedCle.'..' uo~ .'~.,.,,_~T~e ~ ''t c:~rl to 5;.b~'~~~1 .C"~
~~~3i...°v.a~ :.AI~ OAS at~on, speecz data 26 arbd a check p~r tio~ Z8 such as a CRC
f or cor= ec t~.ng err ors in the speecz ca to 2 6 .
~5 In cr~e°~ ~.o ensure that the cV~aecr signal is a n~e~, v~r~ ~~i ~'c°~~'~ 'b~7~'1~~~~' G:~ a:'~21,~c't.?. ~ 8 , ~~'1 ~h~ s~:~~ ~~~a~
s~.c~t t ~,a~ eve.~~. fra~~ y", L.~~e twa~~vh sea4~.mc~n 8 de3ays the t;.~n~ caf teans~3~~s~.o~ ~~~t~3 thp ~u~~~r~ X35 tc~ a par tic,uJ.,a~' sate~~~.te tU cc~mpens~.te :;cad th~ va~~at~,.rans ~y a-.
~:A~F~. ~'t~k7~~z'~,7T.~.~'>:~ ~~3 ~f ~~,~" ~c~:~'.'~~1. S~;ca v ~...Lak~ ~
~~,~ ~..X~~,~.L~t~~' b... ~ ..~ E« ~ t ~.~c?~'~ t~~i~.t ~~,~~~'~~X2~~a~a~x'~~.~. J,c~~~ r~~. ;~~~ K3~~~ ;;.S,o~3~
~' d." Gyye '6°' q y,~ d..
,.he d~~z.~,~<..ent, sa~el.y...i~~.e,s so that ~~~e<,..~ ~ao~;~~~~.~an, axed.
r ange may be ca? cu~.a,tec~ at a~~y :ins ~a~:6=, Ire ac~di.ti~arb ~
3a CA 02432347 2003-06-27 P(.'TIGB951D1103 ' ~O 96103814 _ I3 .
the position of each mobile terminal I8 is det~rmined.
This may be ach ~eved by cor~par ing the deI ays in the signals 3a, 3b transmit~ed fron. the mobile termina? L8 by different sate.? ices 4a, 4b. F:octever, ~'~is method requir es that the signal s 3 are r ecei.ved fr om more than one satellite if an una:abiguous measurement is to be achieved. Because ov blocaage, this :gay not be :w PCSS.'mble. 1"'.enC°,, ad,.rq....~.~~vna~ ~~s~.'~.ol°i s.eeLer::L~.:i~~,.nCj methcds should be used.
3s eac:~ sated l ite 4a, 4b genera'es an array of beams at dif f er en t. a~C~~..es, the ~.ncc:? az° posi ~.ior~ of the mobile te~°:~a~.na~ h8 rel alive ~~ a sate? q to is deLer~~.iled b~ l.den ~..~~.~;~1.i1~' tile L.~~~~ T ~~. Loh~C~: tfe r °
~L~n signal 3 is detected. Tn adGa.it~.Cn, th°_ ~C_L'~ler Sh~f t of the signal 3 is :neasured to det~ane thQ angl a of the mobil.~ ter~i.:~a.':. 9s8 re~a~.a.w~ ~.~ the ~.~~=_.~°ew°;~~,~r~~~ of :~o~i~~ o~ ~:~~~ Sa~~.?'~.1. i.r~ ~ Tie ~~~~ h~'~~.~.~;J1°i ~9::i~?~c~~~ W Jbwi,.~:e tesi~9~:~a1 I~ ys calc~w~..a~~~9ci. by soi~~: o~° al.~j. cap the a.:oo~e tec:~ni~ues .
~9h ~ a ~.~:' v..o ~"~ S t, c~ l . ~,. ~2 %'t Ei ~i.lS. -~ '"'..~,° ~ ~
~3. C~ ,.: ~ ~.°.°". 1Z.''~ t a ~°~
~Jf~'_~~''.er. '.~i~~ ~~ c~!:~~,G.'S1. I'7Clp ~:..3.~ ~._°"~:'::.,~:
~.~1.<°~ 1. ~.i ~, :~aC~ t.~l.~'f, 'u=~. ~.~:..L~~fA
°.a'6.,~.~.:a.~~:~..~.A...1.~..JXi .~i.~E?:1~. ~5,5~''~,%~.7~:
~.~t..>,.~~..:~:~G~.°. i.7~.~..,.~.. ~..:.:.: i:;'.,~Lt'«-,..
J~S~:J~'7,.~.:~.~~:
~.~"' ..L'i.,.',rAC'k~ .~,.~ .~.~ t~~;~~'.~, T.(~t~S"~~~ 3..~'l i."i'_'.~
'w5~""~~V'a.i;3L~'~: ~?.':'~'xi, <, ~ ~llCl~.~a. ~.4; 6..~~';'~?7, t'Y.c~~"'...r-- ~ r ,e3..j ~ ~~~. a~io. 1~..~.. W ,<. ~ , ~ ~ ~..ej, l ~ :~hC>.~~.~c~~. ~~~:,Ca~a~9. T. ~~;9::~ j. i..:l:,t'~j~t..!~Li~eX Za~ha~, e-'z't f 4>~'~ ~ ~Xc?:~~'t_~.E~c~~: ~.''. ~r dete~,'miR~~~ng' ~:~le Laos ~.~v.~.C~x~ Caf ti2~ ~zxc~k~:~.l.~'.
'~.',ex~~~~.Y~a~ ~ E~ a ° WO 9610381~t CA 02432347 2003-06-27 ~~l~aB95~d~1d3 which information may be incorporated in signals tr ans:ni t tad to the ear th sta tion 8 .
The timing of transmission of the return rackets T is sync hronized by the mobil a term~.aa? 18 with the S timing of the reception of the fay.~ard pac.~Cets R.
I
Since the ea=-th s to tion 8 cont,r ols the timir.~g at which the for-~raed packe~s I2 are received, the ~~.my~g of t:Ze i mobil a terwna= I8 is controlled by t:~e eary~h station 8 . Ta allow some :aar c~i.n f or ~°~.iming er r cr , t:'~e t=m:e slots are separa~ed by short ir°dtervals, called "guard hands".
ur t:~e~ore, the conty o l l er 88 of the earn '.h station a meas~z~es the I~~n~l er sh if ~, of the s~.cnal 3 received tram each mobile terminal and cont:-ols ~:.~:e 1~ mcdulation _re~.tency of the R. mcdula;.ors 80' to c.'°7$IleIi~a~.~ ~Oi i»i3.°~. ~C7~'~.~.el" sl~'1..,°.t' so .~.~3a~ '~h~ ~1~C"re'nu~.~:.
1 ~aa is a ~ ways e~ ec:e~.ved b~ t:°~e rtob ~ol~ te~,.na.i,. ~,F~ a V.
the assigned f~°ea~uez~cvm ~y the shave comt~ensatory technigues , which ar a card ied out a t t:ze earth s ~.at~.on 2~ 8 , the pr o~;.essi ~c~~ burc~ee~ cax~ the mobwi.,I~ te~..~ae.l s :~8 ~i~s z;er~cac~~c~ s~~ ~4~Z~,,. ~~~eSr.:~ ~~3~.~.«.b~.~.~.ty ~za~~ be x~r~ckY~a~:~d, ~;~e >~ C~~'~I~W ..,-~e~ .~~..z..,5'Y. I~~'~' ~',J~ ~te~~~ ~~c~d't'fJisx_..~~7 ~..,~i.I~S~..a_~_~"~.~C~ i°4I'~f~.
~;''~'e~ J.~'s'~~' ~~ TC~'s~I~ftf~<~.~~",;~"~:,'.i~. s~.~:, ~..~7~
CmC.~~%°~m ~~~a~e u,."aa~°X e~~~~ s~.~.e.'r,li.~e may be ~~~.ectec~. c~-~: ~~j~.
f'e~~~ra~=d, ~.~.n.,~, ~:~~e sz.g~~.:l. I ~ ~.:roztt t~~e. ~a~~~a~. ~v~.c:
~,ca~~v 8 be~.z~c~ txa~.sm~.~~~~-:d tea each. selectec.~ s~ ~~~~al ~ioew. ~raa;~~.,~~~, ' WO 96103814 ~ 02432347 2003-06-27 PCTIG895l01103 timing calculated so that the signals 15a; 15b from the sate? lites 4a, 4b arr ive siatul taneousl y at the mobile ternina 1 13 .
B ~r~M ARRANN G ..~':~1'r' -5 Each satell~.te 4a, 4b has an array' antenna 90, f or comnunica tian :with the mcbi l a te~in<~1 1 ~ , whic:°I
synthesizes a number of over l appi:.g spot beams each having a pr o ~ ec to d ar ea ~ 0 on the each' s sur f ace cf bet~aeer. 1000km and 3000k:n in diame_er , as shown in 10 Figure 7. Tn : igt:re 7, the nadir of 'he satel lite 4a on the ea~h's surface 9.s sa'1~Wn ds. ~l'5~,n'~ ~ and tale nadir cf the satellite 4:~~ is shc~~rn a~ poi.n~ B, °ath the great cir°°le d; stance be:::,reen these poi:.ts being d 1 reoresentad by the horizonta_ axis. '="~e vertmcal axis 1.~ represents dis t.ance a? ong a gr ea t cir c.le orthcgonal to ~'~e great c ivcl a c~onxa.~~~<:n~.ng ~:he na H~.~°s o~ the t~rc sat~:l~ 1 ~..~e~ 4c'~; 4b a ~~,~ 1~-~c')~~x.~" :~ '~.~~'~~,.:~~?. Z..~~ ~..~
~C?c~"'~.~~'.
~~i th~.n. the fc~ot~~vrt .~c~ of one: s~~t bead;;. of the satellite 4a and P~~.thi.z~ the foot'orint SI. o= a soot C 0 bead66 ~~ ~i~e J4~~e-i.?..vi... .1~.~ ~~9', :a~.i ~e~.~,l~s.
~.a~~u~~.cv.~..~i~,.e.~w,~~ .~s KIC~s~' ~)_~:.~; ''v('i.c'~ F'~ j~'~::~'l~5'- ice, v..~-''..~ L
'L. ~C~ C~ .
~::It°,h ~.?~'..Ywr~'t' d.,r1''.~!t'~.1:?rl ~(a iat9u~d' ~~"O~j-C..-''C:."A" ~~.:~ ~,7~.'~I~s Gm~~",~.,a.°'~°'~,_°"'~!'~~.~y ~~'C:y'~"'"Ee.'°?";.x.:rk~.j ~~;t_3k)~Si.a1'ls:.~,a~ ~..ij ~~.~~'-~
~%~.k_..~.:.~, f.~.'P~~C:R.
~':i~~E'~~ ~.~G:CUNS
~o-.S ~hQWn ~L..KI ~~_gq~,~~~~ ~, 1..S3e G~~L~t'~ ~f ~h~ ~~~.~~'s ' WO 96/03814 ~ 02432347 2003-06-27 pCTIGB95lO1I03 , surzace is divided by the controller 88 into regions 52 and a sub-carrier transmission and reception frectuenc~ pair is assigned to each region 5Z. Thus, the transmit and receive frecuency for each mobile I
terminal ~8 ara determined according to the: regian 52 in which it is located, the regions 52 being fixed relative to the ear 'h's surface. 5 sample spot beam f ootprin t 5 o is s::cwn over lagp:.ng a gv cup of rec_ons 52, which are hexagonal in this exa:~pme.
to When a cal ? is set up, the pos i°ior. of the mebi le tarm.nal Z8 is dete~i,ned by the co;bt.~°s~? lnr 88 of the ear th s ration ~o acccr ddn~ to the tec h::icues descr'_bed grove and a ccr. tr o? sicna l .s tr ansmi t red to the mobile te~ina:. ~8 to assign a pa= ;.icul ar pair of freguencies. These freguencies remain unchanged tr rotz~;i~ou~~ the call unE.~~ess ':.r :uc:~~ve ~.e~.~~,.ina~ ~
3. ~sehf me~ves in tc anotheb~ e:e 11 52~. ~ ~.~,~i c~~:~.? 52 ~.as a rada.us of appr~x~.mate.'l.v 200~~oois_~, sc t~ze ~.~a:~il=
terminal I8 is unlikel v to move ~.~°ea~~entlv between cep i,.s .a2 curing a ca7el . ~t shot~l.~3 :ale z~c~t~~d t~~xa ~. ~:.he s;~.~~ ~.~'tc~ t~~~sit~~~i~°i. c% earl. c~e?.l ~.~de~~.ue~i ~~a9.-rh ~m~e°:eYea~~cTe ~:,c~ ~:.~v~ ea~'~.:~~.'s s~zb~.~~.~°;.~ ~r.c~.
not. to a sa~el~. itNQ ~aeaa~~~
~n another al ter na '~ ~.v~e, the a ss.~.g-c~mepW o~
sequence (soa4called "freg~ency k°Aop~a:~~~~") .
CA 02432347 2003-06-27 pCTIGB95101103 W ~ 96/03814 ~2 Ayl of the aabile terminals I8 within the saes cell ~2 transmit and receive at. the same pairs oL
frecue.~.cies f~ and fr, and t::e sicnal s frog the difrer e:.t mobile terminals ? o ar a separated using TDM.'~, as shown i n r igur a 6 . S ince the dif f er en t mobil a terminals 18 ar a ccn rained within ~-~.he r ela tivel y smal l , f fixed ar ea of the cp l ? and are all at aprroxlmatoly t:~e same dis-~:anca frc~a any one satell_ te, the var is tion in th a uplin.~C pr opaga ~zon delay between dif ~ er ent mobile te~ina? s and any one satellite ~.s limited. In t:~i.s way, t:~e problem of inter f er ence be tween s ~,gna? s i.n ad J ace: t time s? o to is s gx ea ~.1-.° r ad.uced .
f ass ~ CTn~~a:i.~ 0 4. re~.~..~n~ ~ ~ 1...'~.e s~Ce ~ ~ea~s ~s d2.~e~..°_..'lE,'~ ~ ~.. ~.j?~'. ~at~.? ~ 1.~T_ ioc 4' r~r c~a.°~ ~m ~. ~'a't~ 5 t~ d:.On 8 so e::at ?~andc~~re~' of regions ~ ~ be~weere sa~~t beam areas ~ ~ is tr ans ~aa.x erg t tc~ tb' ~e mc~x~~.1 a to mina 1 'I 8 .
Flg~ur a 9 shows the all oca. tr~c~n oe a row of spot ~U beams .~.~. .~:~a t~,e ~eaz~. p~.;°.~e~°~"~ o.y a s~t.ele~.t,te 4a to (~:~ Clg~,~2~ ~;l f Y yc~X'Y,~Lkna °~ ~ o='.. i Ca.I,~~E~ P~'~ ~.:~.~:3 ~ ~ o ~.ea.''t~:F~'f '~.~~~ Z'Z "
d ~. ~' ~=c~ ~..E~ ~,~ a~'. c a ~~ t :;'e ~:3 Via. ''c: c~ C.° :~. ~:z , c~ ~r, ~ » z r; ~ a ~ :z;" ec~'~. ons 5 ~
o~~ t~.e su'~vac~e r~a~ t'~e eax~°',_vi~.a ~~b t~:Le satellite ~3~'"~a~; u=~~c~~ ~"x~ 1y''~~ ~~ ~.'°_t~t~ c~; '~~'~,~~ ~w~~ ~.
.~7~~~u~ ~ y are ~~ad~.~?'~~Iga~l~' :~"~~e~;'d ~~.~ c~~ '~;~ 1~":?:acx.~.lt ~~a~.~"~.~.:rtr~~
~~ thelZ' ~O 96Id38I4 ~ 02432347 2003-06-27 PCTlGB95101103 resr~ective cent: es C.
after Ta, the elevation angle oy the satel 1 ite 4a with respect to the centre Ca becomes undesirably low °or reliable ceamunication. The earth staticn ~
detec ~s u'~e posi Lion of the centre Ca wi th rsspec ~ to the satel 1 ae ~a and controls the sate? lute ~a by sending cortrcl s=gnats to redeploy tze bean a1a to a .new cen tr a C:~ . By this tire , another sa tel? i to ~b ( no shown in Figure ~) is already cover.ng the regions ~2 around the cents a Ca wi th one of i is spot beams , so ;.hat sa tedi ~.e-~t~--sa te? lice hanc~dcver ~.s ach~..eved without any in~er::uptic~n of the co~..~uzm~.catzon se~r~.ce.
time T;, all of t:~e spct beams 5~ have beer.
=edeployed except øor the bean Sln.
f ~.a Thus, v:~e covew age ar ea o~ the ax~teenna. as a whol a .
E
moves p~°cgr ~ssm.vei y fo~-~r~.~':~, ar~c3 t.°~.n ~~ taro~~:
~:r e~:..~.~ v v" 1 .,r,e~ .~.~~ ~s 'v ~ ~ ~° t~ ' Ce~:~~I~.ds~.~~."~~,~~
G~M,~;=~~.:ar Q~ foca~ ~.~~~c~....~~~x~ ~~.~~.~.rhs o~.n~i~.~~~ ,~.ay bed ae~ the sate ~.~ a~~e..
The coverage ar ea of the spot beams ~ 1 0~ tae 2Q satellite tea, ~x°oc~'h:°ws~e~a ~..n a fa~~a-~~i~r~ ~a~a.c~x n~.~r :~~e :~.a,~e~~e~~ ~.cw ~,4~~ F;x,°~ie~~ ~~t= cap; a c~ cpe~°°
) ~...1 ~.a.x ~a:~~ ta~~t.
~;~q~~C~, ;~$~..'~EL'.'Xvd~.x4~ ~~C.~i; ~:)~?t'~~T'1'a' '~C~
~G7Y? ~,ra,~~,;,.'1k"1C~..7~."~'~~~ C.~~,~' ~..~.~~~''~k~:t~ ~J.~,-.~.~,'bA~, ~:~_Y's;~('~.~.9~~:,':', .~, Q.:
, ~~.aCN~ ,6JE'~r~,.~.~~.,c,~"r R .y-.
:f.~~:>>~.~ ~.~~L~~ ~1-i~. f.~t~gi''C.~ ~! .r'3 ~ ,.i.y b~l.~~.~~.y s ~.PcA~.~a.<.3, f'~~~.m~~~~, '~~._~ ~'wIl~~~.
~~kX~'s'~.' ACA ~9...~, .~.'~ X'~ec2.C'i.l,~'_.~"-~C)t,:l<y:asv~~2$~)Sb:$:'~.
'~.~E" c~'~3~!i':"Y
9f3~~..t~Q%'~ C~ ~ :1_, ~, t~lE' ~aec"~~ ~9a~~."~,.~~e'11, .~_ ~=
k~'l~el"1 ~ ~~"~~'~r~.t~~~'~'C:~
i: r:;y CA 02432347 2003-06-27 pC.°TIGB95IOi143 the outermost f or~rar d posi Lion . However, the over all beam pattern projected by the antenna of the satellite 4 a progresses on a cor. ~.inuous tr ack over t.~:e ear--~.'~ J s surface Wl.th the procression of the Satell ~~e. '~'~is ne thod provides r educed fr ecz:enc_r of .'~.ea:a-te-ream.
hangover , although i t does no t reduce the yr ecuencr of sate? l ite-to-satel l i t~ i~andover .
Pr 2~° e'a~~ y, the ear t h S t~,tl.On 3 C~Tl;~'_::LIOUS~V
C3eter~? neS t:~F? CUrr eCt d.'..r eC~.~.Qn f Cr eaC.'I Cr '.':e ~~3B~S
51 and sends control slgna?s 'o t he sate'_? 1 ~e ha to control the direce~r9n of the beams S? . However, the means mC°m., det~~...d3.9..t~x~dl~ 1.d"?~ P~eadil d.'...~°'.eC,..~.CnJ 1'~la~l alternatively be incorporated ~.n the sate_.~i~.e, W In a separ ate gr ound-based sa tell~.te con tr o 1 s to t=on .
I~ SECOND ~'30D_:~!YN'~
r''~ S a e~ r.7 d . C a ~.~s C;e d .i..".a!, ~. '.~. s". rd r. ..'. ~. '~ r ~°° ~ ~ C ;y 1~ ~° ~w AaC7,~J Are desC.. a ref°G9Y°~3~eTiy~°~a tC ~~.g't~ '~'aae°3 ~. tC7 ~, ~,C) a%3C ~a.a The seCe~sn(~
E.'~7t~CbJs.~~'f7,~ ~,T.~~~e~S ~'iv:.~Yi, ~;,Y~.e C'.~C9d3.~en~ ~~~e ~~a~~'~: Ln opera tion of the ear m:.~ s ration 8 , mobile terminal al ~ , ~- A arlt~ 7 ~:~7,~~. i~lc~.Ci,~I a and sat~~~..:....~~.,as ~, ~ f. '~,g'i~ v,.~Z~i~~.I~~.7,.
~'e~>e ~.v~'S 48:~.,~X~~. ~~ ~ ~;t;',~~~a C~,~.,f S~ ~a. .~ to .~ ~?~.'.;'s "~.
~,. .A.. n~ ~'~". a i ~.. ~..~ ~~~ wd ..
terminal I8 is unlikel v to move ~.~°ea~~entlv between cep i,.s .a2 curing a ca7el . ~t shot~l.~3 :ale z~c~t~~d t~~xa ~. ~:.he s;~.~~ ~.~'tc~ t~~~sit~~~i~°i. c% earl. c~e?.l ~.~de~~.ue~i ~~a9.-rh ~m~e°:eYea~~cTe ~:,c~ ~:.~v~ ea~'~.:~~.'s s~zb~.~~.~°;.~ ~r.c~.
not. to a sa~el~. itNQ ~aeaa~~~
~n another al ter na '~ ~.v~e, the a ss.~.g-c~mepW o~
sequence (soa4called "freg~ency k°Aop~a:~~~~") .
CA 02432347 2003-06-27 pCTIGB95101103 W ~ 96/03814 ~2 Ayl of the aabile terminals I8 within the saes cell ~2 transmit and receive at. the same pairs oL
frecue.~.cies f~ and fr, and t::e sicnal s frog the difrer e:.t mobile terminals ? o ar a separated using TDM.'~, as shown i n r igur a 6 . S ince the dif f er en t mobil a terminals 18 ar a ccn rained within ~-~.he r ela tivel y smal l , f fixed ar ea of the cp l ? and are all at aprroxlmatoly t:~e same dis-~:anca frc~a any one satell_ te, the var is tion in th a uplin.~C pr opaga ~zon delay between dif ~ er ent mobile te~ina? s and any one satellite ~.s limited. In t:~i.s way, t:~e problem of inter f er ence be tween s ~,gna? s i.n ad J ace: t time s? o to is s gx ea ~.1-.° r ad.uced .
f ass ~ CTn~~a:i.~ 0 4. re~.~..~n~ ~ ~ 1...'~.e s~Ce ~ ~ea~s ~s d2.~e~..°_..'lE,'~ ~ ~.. ~.j?~'. ~at~.? ~ 1.~T_ ioc 4' r~r c~a.°~ ~m ~. ~'a't~ 5 t~ d:.On 8 so e::at ?~andc~~re~' of regions ~ ~ be~weere sa~~t beam areas ~ ~ is tr ans ~aa.x erg t tc~ tb' ~e mc~x~~.1 a to mina 1 'I 8 .
Flg~ur a 9 shows the all oca. tr~c~n oe a row of spot ~U beams .~.~. .~:~a t~,e ~eaz~. p~.;°.~e~°~"~ o.y a s~t.ele~.t,te 4a to (~:~ Clg~,~2~ ~;l f Y yc~X'Y,~Lkna °~ ~ o='.. i Ca.I,~~E~ P~'~ ~.:~.~:3 ~ ~ o ~.ea.''t~:F~'f '~.~~~ Z'Z "
d ~. ~' ~=c~ ~..E~ ~,~ a~'. c a ~~ t :;'e ~:3 Via. ''c: c~ C.° :~. ~:z , c~ ~r, ~ » z r; ~ a ~ :z;" ec~'~. ons 5 ~
o~~ t~.e su'~vac~e r~a~ t'~e eax~°',_vi~.a ~~b t~:Le satellite ~3~'"~a~; u=~~c~~ ~"x~ 1y''~~ ~~ ~.'°_t~t~ c~; '~~'~,~~ ~w~~ ~.
.~7~~~u~ ~ y are ~~ad~.~?'~~Iga~l~' :~"~~e~;'d ~~.~ c~~ '~;~ 1~":?:acx.~.lt ~~a~.~"~.~.:rtr~~
~~ thelZ' ~O 96Id38I4 ~ 02432347 2003-06-27 PCTlGB95101103 resr~ective cent: es C.
after Ta, the elevation angle oy the satel 1 ite 4a with respect to the centre Ca becomes undesirably low °or reliable ceamunication. The earth staticn ~
detec ~s u'~e posi Lion of the centre Ca wi th rsspec ~ to the satel 1 ae ~a and controls the sate? lute ~a by sending cortrcl s=gnats to redeploy tze bean a1a to a .new cen tr a C:~ . By this tire , another sa tel? i to ~b ( no shown in Figure ~) is already cover.ng the regions ~2 around the cents a Ca wi th one of i is spot beams , so ;.hat sa tedi ~.e-~t~--sa te? lice hanc~dcver ~.s ach~..eved without any in~er::uptic~n of the co~..~uzm~.catzon se~r~.ce.
time T;, all of t:~e spct beams 5~ have beer.
=edeployed except øor the bean Sln.
f ~.a Thus, v:~e covew age ar ea o~ the ax~teenna. as a whol a .
E
moves p~°cgr ~ssm.vei y fo~-~r~.~':~, ar~c3 t.°~.n ~~ taro~~:
~:r e~:..~.~ v v" 1 .,r,e~ .~.~~ ~s 'v ~ ~ ~° t~ ' Ce~:~~I~.ds~.~~."~~,~~
G~M,~;=~~.:ar Q~ foca~ ~.~~~c~....~~~x~ ~~.~~.~.rhs o~.n~i~.~~~ ,~.ay bed ae~ the sate ~.~ a~~e..
The coverage ar ea of the spot beams ~ 1 0~ tae 2Q satellite tea, ~x°oc~'h:°ws~e~a ~..n a fa~~a-~~i~r~ ~a~a.c~x n~.~r :~~e :~.a,~e~~e~~ ~.cw ~,4~~ F;x,°~ie~~ ~~t= cap; a c~ cpe~°°
) ~...1 ~.a.x ~a:~~ ta~~t.
~;~q~~C~, ;~$~..'~EL'.'Xvd~.x4~ ~~C.~i; ~:)~?t'~~T'1'a' '~C~
~G7Y? ~,ra,~~,;,.'1k"1C~..7~."~'~~~ C.~~,~' ~..~.~~~''~k~:t~ ~J.~,-.~.~,'bA~, ~:~_Y's;~('~.~.9~~:,':', .~, Q.:
, ~~.aCN~ ,6JE'~r~,.~.~~.,c,~"r R .y-.
:f.~~:>>~.~ ~.~~L~~ ~1-i~. f.~t~gi''C.~ ~! .r'3 ~ ,.i.y b~l.~~.~~.y s ~.PcA~.~a.<.3, f'~~~.m~~~~, '~~._~ ~'wIl~~~.
~~kX~'s'~.' ACA ~9...~, .~.'~ X'~ec2.C'i.l,~'_.~"-~C)t,:l<y:asv~~2$~)Sb:$:'~.
'~.~E" c~'~3~!i':"Y
9f3~~..t~Q%'~ C~ ~ :1_, ~, t~lE' ~aec"~~ ~9a~~."~,.~~e'11, .~_ ~=
k~'l~el"1 ~ ~~"~~'~r~.t~~~'~'C:~
i: r:;y CA 02432347 2003-06-27 pC.°TIGB95IOi143 the outermost f or~rar d posi Lion . However, the over all beam pattern projected by the antenna of the satellite 4 a progresses on a cor. ~.inuous tr ack over t.~:e ear--~.'~ J s surface Wl.th the procression of the Satell ~~e. '~'~is ne thod provides r educed fr ecz:enc_r of .'~.ea:a-te-ream.
hangover , although i t does no t reduce the yr ecuencr of sate? l ite-to-satel l i t~ i~andover .
Pr 2~° e'a~~ y, the ear t h S t~,tl.On 3 C~Tl;~'_::LIOUS~V
C3eter~? neS t:~F? CUrr eCt d.'..r eC~.~.Qn f Cr eaC.'I Cr '.':e ~~3B~S
51 and sends control slgna?s 'o t he sate'_? 1 ~e ha to control the direce~r9n of the beams S? . However, the means mC°m., det~~...d3.9..t~x~dl~ 1.d"?~ P~eadil d.'...~°'.eC,..~.CnJ 1'~la~l alternatively be incorporated ~.n the sate_.~i~.e, W In a separ ate gr ound-based sa tell~.te con tr o 1 s to t=on .
I~ SECOND ~'30D_:~!YN'~
r''~ S a e~ r.7 d . C a ~.~s C;e d .i..".a!, ~. '.~. s". rd r. ..'. ~. '~ r ~°° ~ ~ C ;y 1~ ~° ~w AaC7,~J Are desC.. a ref°G9Y°~3~eTiy~°~a tC ~~.g't~ '~'aae°3 ~. tC7 ~, ~,C) a%3C ~a.a The seCe~sn(~
E.'~7t~CbJs.~~'f7,~ ~,T.~~~e~S ~'iv:.~Yi, ~;,Y~.e C'.~C9d3.~en~ ~~~e ~~a~~'~: Ln opera tion of the ear m:.~ s ration 8 , mobile terminal al ~ , ~- A arlt~ 7 ~:~7,~~. i~lc~.Ci,~I a and sat~~~..:....~~.,as ~, ~ f. '~,g'i~ v,.~Z~i~~.I~~.7,.
~'e~>e ~.v~'S 48:~.,~X~~. ~~ ~ ~;t;',~~~a C~,~.,f S~ ~a. .~ to .~ ~?~.'.;'s "~.
~,. .A.. n~ ~'~". a i ~.. ~..~ ~~~ wd ..
5.
~ 5~.~:~~hia'3 ;~t.t'Z ~''~L~~~i~.~.'_ 1.~, ~~jC3 ~tdf~K~? ~.EM i'~t xs.'~.~~..~. ..! ~3 ,, Cc~.~T~~it~~~'g _, ~ ~t t. W.. ~ :'t.'~ is:, t r. .~
time slots t s~r~,t..~~.~ n a rapes tiny ti.~~~ frame ~;~,. va.a v~Ze ' WO 96/0381.1 CA 02432347 2003-06-27 PCTIGB95101103 2~
first and second satellites 4a, 4b, or via firs and second beams of one satellite, at pairs ef f:°e~uercies f 1, f 1' and f,, f,' respectively .
In the example shaven, the ea~~h station 8 S tr ansati is a packs ~ Rx~ in time slo t t: via t::e ='_r s t satel 1 ite 4a, which packet is received at frecuenc~.r fl by t::e mob:.le ,.e~inal 13. The :nubile terminal 18 then transm=is a packet Tx, in time slot t3 at the frecuency f1' via a beam gene=ated by the satel 1 ito 4a.
The ear th s ration 8 transmits a packet R.~c,, con ta:.ninc the same ? of o.~.aa w~.on as the pa~;~cet fix, , via t:ae second sat.el l ire 4b, ca via a fu:~ ther beam generated by the ,, sa ~emli to 4a, cerh ~.:: h r et °ans~a~ is the packet :~2x, to the mob i 1 a te~i.~.a 1 :.3 a t fr ecuency f, i n time s T o ~ is .
L~ The maa~~.eQ d°~r.~.a~. z a they t~°anS:n..~.tS a pacxe~
'~x., coz~.:.a ininr t he sam a inf orma t ion as th a packs t ~'.;; , in r~.:~e s.~_ot t.,. at the ~:~°ec~"~aen~y f,~ . ~'he pac:ket 'I'x, ~,s a t3~ ansm~,. t red to t~~e ear th s tat 4ax°~ ~ by t.~ae sec~~~°id satellite 4b. T.~, t:zis wav, the c~aratdcl?e~- 59 has S~.~t~" ~ .''LIZ, ~:L~ t~~e ~C ~e~~.$Y'3~ '~:h~'- ~i illC~''C~l~' ~'~'.Cd b ~
Ctr,' e3,~~.~~~r.ca~~~,.R~.~~:(~,C' -7C? Gr~Q'1aX " ~.,~a~ d5s x~-v'~.. ',.
c~ i ~. ~ sn~..~a~~ ;~,~~~e swo4.ca, ~~°~°.~'~'iic~. ::~.~1'~'.1,.~'', t'axC:3 ,~~.T~' ~'~,~'?'t'!~)C~,'l.l.~.~3.tv.~'~"v c'~.l"lt:~. ~edC7 h<''~'~
~~zue~? t;~? the frec~~en,c~.e~; ~~F amd f? aabd. ~';~ anc~ ~~;
~ae~r tk~~ z~c~b.~w~~P ~:ei.x~~:~, ~~as ~n"e~..~:ta.~~wr~ ~,oth CA 02432347 2003-06-27 p("TlGB95l01103 packets Rx; and ~c,, the packet decoder '72 combines the two, or selects the better packe~, for~ conversion to _ speech, as in t:~e first eanbodi~nent. Similarly, the ear t:: sta~.mon 8 c~mbines the twc t::ansmitted packets Txi and Tx, ~~ selects the bettea packet, to improve the coal ity of the signa, t~ans:a:.t'-~ed to ~..~a ?STN 9.
t:: t:°~is example, each t~.~e f::a:ae v comprises eigh- time slct.s d, so that eicht ~ob'_1 s te~ina? s 18 can cc~ur.~.ca to wi th the ear is to t ion 8 a t t..he f~ecT~enc~.es fl, ',' , f, and '.' us:~nc TDM.~. :iowever, the al:~ucation od tire slo~s ; s __~.e:~ ~r~i e, to epti~ize the nc:~beow c~f users and aue,l ~.~:'~° ' c~;ra.-au::lcat'_on, as desu~'bec below.
Du:.~-_..~.c cal'_ set9up, the :acb:.le ts~rnal ? 8 1~ man~°o~s : plot s~.~na~.s L~ans~~.tta:~ pV the Sate:.'rtes 4r 's~ Cl~'t~~~l.r:.:le xi%':~.C~C~ ~~.L~.'.'..'.'.ai"~~S ~,~'°:
.'.~i.l V~eW aITG~
C '"~ &3 'A.i .a, v c~r~et4be~ a.t~'~ sa,..4.,.a...ult~~._ .~.nk°..; ~~..~ c!~_c~. Th:.s .'..na a~d'~"°'u°~a t..''..ode ~~ tm "'G.il~l""'a~.~ bV.et~
lea~'3 ~:a~~'...' ea~ taa ~ b:a ~~ 'L°1'~a $ . Zi only one sa tel l ~. t a i s in vi eW , ~.he ear th s to Lion 8 n a1 ~.~ac:~.;~es wr~~.y c~r~. ~:.T~~z~ s'.c~t ~°cart~°
~d°ans~~s ,~.on and orxe ~:7~° ~'r°~.~C?k~ ~.'-.,c;3.~7. c~, e.. ;; ;z~= ~:1~°~
?..'-; ~y . ~',::' 'w.;:~.i?C .9.. ~~:i ~~~~ ~''eSDCXIt'~.:'~~t~~
'~.i~ '~..~~c~. ~w, SCS'i~FYa. ~ ' l ~°' , ''~°Bl~ s11~'i~i ~.~
~"' icy"'. , j..,..lc'. ~, ~ ~ ~on.5 't".~'.~~c:H
the p ~.:~.cj'~. ~ s.~;:~m.l ~ ~.~~~~_-.~ p~ ~, t~~~: c~~ 1. ?,.~ ~~a u~:at , if anc~~,he~,:, ~~'~E'.~..' '.~C"'E? C°axilE':~ '-:Sti C)- ~.lY~~~! . y_ur~'i~
~sAC';.~5.. 7.~ '~:°r~. lna~ .~.Fa J S ~;c~~~~,r~.~rk.~.~~~ ~.~~;~ t~3~.~ t.~~~=~:a:~ a~~. ~.~., ~~--A a G,~ :-~~.~ ef ~-~.h ~tatior.~ az~~~
fc~~~-~:~~~:~n ~;~'~r~~.~~9.~° ~:.~:c~, x.wce.~.~:e ~.~..:,a,~
~5.c~~:~r aye alloca.te~d, ' ~O 96/03814 CA 02432347 2003-06-27 1'CTIGI395101103 at the pair of frequencies corresponding to the other satel?ite. although im the above example two time slois ara allocamed far t.ransmissicn by the mabile terminal 13 , onl y one of the time slo is nay be Cased i~
the r eturn 1_:L~ is sa ti sf ac Cory in or der t.o conserve power and reduce el ectromagnetic emissions, which is oar tic°al arlv imaor 'art for hand~hel d r.obi? a ter~ina? s.
.-_.,, ; or ~9 of the mobile te~.na; ~.3 '"he Con,._~dr~_ moni tore the ~ua~ i ty a ~ ~ igna 1 r eCn ived f r ~~1 batl 1.0 sate_lit~s 4a and 4b and normalcy :~ransmits only dur ing th a t ime s 1 o t and a t the fraguency carrespcnd~~ ~.~ "'~ '~ ";'°' yro~. 'al~i~~.~ the stronger l 6 g ~. V 1r '. ,..5~ ~
s'..s nal ."'~S ..c~.'~deC.. faoweTier, ~,... tml~ seleC'eCi ~°_6.."'~ri'1 link provides only a caea:~ signal , as in the case eø
.'7 X111 t~pa~..°: .'.aG~:lgp tile earth Sva~.''.,Cle~. o CO:~IL;.r.'~Ca°es dh ~s ? r.: ~...r~c3.~aC7%i t'J t~e ~Oi ? ~.° ~;~:'.."~'~.~.nc'il ~..'~
anCs e.a ~' a~~ea°'~a~~'._'.,1I~ °~''.'ess~~~;'a l~P9x .'MS s'~..-'~~'Ce.e~.
~ 5~.~:~~hia'3 ;~t.t'Z ~''~L~~~i~.~.'_ 1.~, ~~jC3 ~tdf~K~? ~.EM i'~t xs.'~.~~..~. ..! ~3 ,, Cc~.~T~~it~~~'g _, ~ ~t t. W.. ~ :'t.'~ is:, t r. .~
time slots t s~r~,t..~~.~ n a rapes tiny ti.~~~ frame ~;~,. va.a v~Ze ' WO 96/0381.1 CA 02432347 2003-06-27 PCTIGB95101103 2~
first and second satellites 4a, 4b, or via firs and second beams of one satellite, at pairs ef f:°e~uercies f 1, f 1' and f,, f,' respectively .
In the example shaven, the ea~~h station 8 S tr ansati is a packs ~ Rx~ in time slo t t: via t::e ='_r s t satel 1 ite 4a, which packet is received at frecuenc~.r fl by t::e mob:.le ,.e~inal 13. The :nubile terminal 18 then transm=is a packet Tx, in time slot t3 at the frecuency f1' via a beam gene=ated by the satel 1 ito 4a.
The ear th s ration 8 transmits a packet R.~c,, con ta:.ninc the same ? of o.~.aa w~.on as the pa~;~cet fix, , via t:ae second sat.el l ire 4b, ca via a fu:~ ther beam generated by the ,, sa ~emli to 4a, cerh ~.:: h r et °ans~a~ is the packet :~2x, to the mob i 1 a te~i.~.a 1 :.3 a t fr ecuency f, i n time s T o ~ is .
L~ The maa~~.eQ d°~r.~.a~. z a they t~°anS:n..~.tS a pacxe~
'~x., coz~.:.a ininr t he sam a inf orma t ion as th a packs t ~'.;; , in r~.:~e s.~_ot t.,. at the ~:~°ec~"~aen~y f,~ . ~'he pac:ket 'I'x, ~,s a t3~ ansm~,. t red to t~~e ear th s tat 4ax°~ ~ by t.~ae sec~~~°id satellite 4b. T.~, t:zis wav, the c~aratdcl?e~- 59 has S~.~t~" ~ .''LIZ, ~:L~ t~~e ~C ~e~~.$Y'3~ '~:h~'- ~i illC~''C~l~' ~'~'.Cd b ~
Ctr,' e3,~~.~~~r.ca~~~,.R~.~~:(~,C' -7C? Gr~Q'1aX " ~.,~a~ d5s x~-v'~.. ',.
c~ i ~. ~ sn~..~a~~ ;~,~~~e swo4.ca, ~~°~°.~'~'iic~. ::~.~1'~'.1,.~'', t'axC:3 ,~~.T~' ~'~,~'?'t'!~)C~,'l.l.~.~3.tv.~'~"v c'~.l"lt:~. ~edC7 h<''~'~
~~zue~? t;~? the frec~~en,c~.e~; ~~F amd f? aabd. ~';~ anc~ ~~;
~ae~r tk~~ z~c~b.~w~~P ~:ei.x~~:~, ~~as ~n"e~..~:ta.~~wr~ ~,oth CA 02432347 2003-06-27 p("TlGB95l01103 packets Rx; and ~c,, the packet decoder '72 combines the two, or selects the better packe~, for~ conversion to _ speech, as in t:~e first eanbodi~nent. Similarly, the ear t:: sta~.mon 8 c~mbines the twc t::ansmitted packets Txi and Tx, ~~ selects the bettea packet, to improve the coal ity of the signa, t~ans:a:.t'-~ed to ~..~a ?STN 9.
t:: t:°~is example, each t~.~e f::a:ae v comprises eigh- time slct.s d, so that eicht ~ob'_1 s te~ina? s 18 can cc~ur.~.ca to wi th the ear is to t ion 8 a t t..he f~ecT~enc~.es fl, ',' , f, and '.' us:~nc TDM.~. :iowever, the al:~ucation od tire slo~s ; s __~.e:~ ~r~i e, to epti~ize the nc:~beow c~f users and aue,l ~.~:'~° ' c~;ra.-au::lcat'_on, as desu~'bec below.
Du:.~-_..~.c cal'_ set9up, the :acb:.le ts~rnal ? 8 1~ man~°o~s : plot s~.~na~.s L~ans~~.tta:~ pV the Sate:.'rtes 4r 's~ Cl~'t~~~l.r:.:le xi%':~.C~C~ ~~.L~.'.'..'.'.ai"~~S ~,~'°:
.'.~i.l V~eW aITG~
C '"~ &3 'A.i .a, v c~r~et4be~ a.t~'~ sa,..4.,.a...ult~~._ .~.nk°..; ~~..~ c!~_c~. Th:.s .'..na a~d'~"°'u°~a t..''..ode ~~ tm "'G.il~l""'a~.~ bV.et~
lea~'3 ~:a~~'...' ea~ taa ~ b:a ~~ 'L°1'~a $ . Zi only one sa tel l ~. t a i s in vi eW , ~.he ear th s to Lion 8 n a1 ~.~ac:~.;~es wr~~.y c~r~. ~:.T~~z~ s'.c~t ~°cart~°
~d°ans~~s ,~.on and orxe ~:7~° ~'r°~.~C?k~ ~.'-.,c;3.~7. c~, e.. ;; ;z~= ~:1~°~
?..'-; ~y . ~',::' 'w.;:~.i?C .9.. ~~:i ~~~~ ~''eSDCXIt'~.:'~~t~~
'~.i~ '~..~~c~. ~w, SCS'i~FYa. ~ ' l ~°' , ''~°Bl~ s11~'i~i ~.~
~"' icy"'. , j..,..lc'. ~, ~ ~ ~on.5 't".~'.~~c:H
the p ~.:~.cj'~. ~ s.~;:~m.l ~ ~.~~~~_-.~ p~ ~, t~~~: c~~ 1. ?,.~ ~~a u~:at , if anc~~,he~,:, ~~'~E'.~..' '.~C"'E? C°axilE':~ '-:Sti C)- ~.lY~~~! . y_ur~'i~
~sAC';.~5.. 7.~ '~:°r~. lna~ .~.Fa J S ~;c~~~~,r~.~rk.~.~~~ ~.~~;~ t~3~.~ t.~~~=~:a:~ a~~. ~.~., ~~--A a G,~ :-~~.~ ef ~-~.h ~tatior.~ az~~~
fc~~~-~:~~~:~n ~;~'~r~~.~~9.~° ~:.~:c~, x.wce.~.~:e ~.~..:,a,~
~5.c~~:~r aye alloca.te~d, ' ~O 96/03814 CA 02432347 2003-06-27 1'CTIGI395101103 at the pair of frequencies corresponding to the other satel?ite. although im the above example two time slois ara allocamed far t.ransmissicn by the mabile terminal 13 , onl y one of the time slo is nay be Cased i~
the r eturn 1_:L~ is sa ti sf ac Cory in or der t.o conserve power and reduce el ectromagnetic emissions, which is oar tic°al arlv imaor 'art for hand~hel d r.obi? a ter~ina? s.
.-_.,, ; or ~9 of the mobile te~.na; ~.3 '"he Con,._~dr~_ moni tore the ~ua~ i ty a ~ ~ igna 1 r eCn ived f r ~~1 batl 1.0 sate_lit~s 4a and 4b and normalcy :~ransmits only dur ing th a t ime s 1 o t and a t the fraguency carrespcnd~~ ~.~ "'~ '~ ";'°' yro~. 'al~i~~.~ the stronger l 6 g ~. V 1r '. ,..5~ ~
s'..s nal ."'~S ..c~.'~deC.. faoweTier, ~,... tml~ seleC'eCi ~°_6.."'~ri'1 link provides only a caea:~ signal , as in the case eø
.'7 X111 t~pa~..°: .'.aG~:lgp tile earth Sva~.''.,Cle~. o CO:~IL;.r.'~Ca°es dh ~s ? r.: ~...r~c3.~aC7%i t'J t~e ~Oi ? ~.° ~;~:'.."~'~.~.nc'il ~..'~
anCs e.a ~' a~~ea°'~a~~'._'.,1I~ °~''.'ess~~~;'a l~P9x .'MS s'~..-'~~'Ce.e~.
6 ~.L~°m,~~~~a~ ~ p 7~f a Cj'~a."f~~ ~~.'~
nl~.:°'~1J.~'°P~~ G~' L7.yy~,'.~'~ ~A
be aCC..'OCCav.2d a'C any.a:~E.' , Only one t.l.~e s l a'L i.ar eaC~'I. C3 u,. ~.°'a.'''°au~l. a'.'~' m.C~~'1 c~~AC~
~"'e~°e%y~.~t~.an LTka"V" .Ce ~~..~ oCa~eC°~ t~
c~ r? C t~, ACIt~J'7 ,°.. ~ ~' ~ 'E..~:!~: i"~ ~. ~°~~L ~. Z, i'~
~~' X'~~7Tlt~ ~:3~; ~1~~.' ~e~'~°~~'1 ~ ;:."r-~'_S T?Y C'J ~ :,C7c :~ 1 ~ .c ,... .y ~ ~ ~.. ~7 ;~ ~° ,y r ~, , (... ~ :' ° ~ !.° ~" ;
t~ i'~
,.as ~ [ _~ n'..'s ,~ c.~. . ~: f,~ ~' ~ ~'t.::... G~... ~. ~..'~.~ , Wit. , ~. .,.~ _ ~ K~.'. ~, ~;~, c"~ U:. ro_ r f ~. .: "A.
e_. h, . _ ~ V ° . .k-. .o 1.4"~ E~~C, u.,l .~ w~~-..C'~S°9. ~ alt~~ ~5~,~' l;~Z')_t.C:~=! C~c' u.. w. _ .~'c <~'I\d3.(~1~(z ,f:d3l..C.~
1 ga err K'y cei:.'~,~,~ M ~~~'a37. ~~ ~s~5',~:6a ~,9tv ~,._i k.'i~ 4 >~ x 'l>
~~'a~ae ..n . cA..i~'~ , 13,~ :~a.i.r3~e~Ai. ~ x:d ~~~,.f~°~,7 ~°'Fz !,:~ p '~hEs f~ E'CXll'~I~f_."~.au'~'J ~~1 p ~~:~j '' f~~ Fz ~.1'~'.s:'!. .~" Ca:~.
communication via only the first satellite 4a. The voice data encoded in a single packet Rx~ or Rx: in the embodiment shown in Figure 10 is divided between t~.to =
packet$ Rx, and Rx, which are transmitted at the frequency ::' by the eart:~ station s at half the normal baud rate in time slots tl and is respectively.
Likewise, the voice data transmitted by the mobile terminal 18 is divided between two packets ' Txa and Txb in each time frame F and transmitted at the frequency fl' in time slots t3 and t~.at half is the normal baud rate. The reduction of baud rate reduces the probability cs bit e_~ors.
Alter.~.atively, two satellite beams aa.~ be used for transmission and reception, and the packets fix,, Rx, and Tx" Tx~~ aay be divided between t:~e two beams.
The above technique of selecti.~.c a ? owe. baud rate and dividing t.~e transmitted sig:.='_ :,to two or mare packets may also be employed in the first embodiment.
$BN~g~
~ In the second embodiment, the satellite beams are not steered but sweep across the earth's surface at a constant rate as the satellite 4 prcgresses in its orbit. As in Figure 7, the beams overlap so that the mobile terminal 18 is able to communicate via more than one beam at least some of the time. Furthermore, beams from different satellites 4a, 4b may overlap so WO 96/038I~i CA 02432347 2003-06-27 PCTIGB95~OI103 t~.at the mobile terminal L8 is able to communicate via more thar. one sate? ? ite 4a, 4b. Transmission or reception fr ecuer.cies are allocated according to the spot beam in which the mobile terminal .18 falls and not accordinc; to the position of the mcbile term~.nal 18 on the ear t h's sur~ace. As the beams of eac:°:
satel l ite 4 swee:; o~rer the earth 's surface, the mobil a terminal I8 wi" oass fr oz~ one beam to the new and a call wi l= the= e_-':.re need to be handed oveT~ fr om beam l0 to beam to reach the mobile termi:al 18. This is ach ieved by dete~i~tinr at the earth station $ which beam the mo::ple :.einal 18 falls within and al? cca ring a ca ~a.~ w i, th ~:he mcb i le te~i.ral.
Is i:~ th a an~roar fate bea.:.. When the mobi? a terminal ? 8 is lv handed over to a new beam, a coanman.d signal is sen t to the rcc~b ~. : a te.~:~en~a ~.. ~ ~ ~.s~~~-~ lading ~..:~.~:
~orma tion nn tAe i ~~".~1~ s ~a~'bW:'. ~%1~ the t:,'.'~.a~.~;.'ct i~ ~n'G
.'.'e~:~~"'~~. f~~'eCa',,~e~'~:M~C'.~
to be user by' t~ae mobi? a ter~l.na1 b~'~ ~:.a~e net~~
beam, a2'~~.
the mobile te~i.nal thereaLter uses the new 20 fr e~.ae~~c~.es and time s? ~':~ indics,ted i~? the command ,1.. ~.r: b. ~.~.~ ~~bl~.i,.~~ ~,.~r-~. ks.y~~.~ ~.l.QS
tA~at ~~ ~ ..~..~ i~~~ ~ ~ a '.~'t~a ear.v~ k=2. s ~e.t ~.c~ E~ ~x~av ~ma anv c5~~ a x~ezmber of ~~.Y ~? T, q. ~:~ r.A f,:a ~.~...~~ t t~ ~';dR,x? ~. C~;
t a ~ s~ r c'a E: i ~ ~'. ~ r"~3 t,. n E~. ~: .--~ t~s'z ~, ~,: ~1, i"~ t~ ~d ~:l:a~". ~7~C,a~~J..~~.~ "~.~~e~,:z~~'ic3. ~_ :i..~ 'f::.C'J
b~ h~a~~:~~~~:3 C~d'e~o ~.~~~a ~dt'R~~:~
~r i9 r ~ ~~
$'7~c~' ~~1 ~~ ~ ~"r~~ ~ ., :~ w. ~',~ 'e.4~.~ ~,. ~.J
~" ~. C: ~ ~ ~5.~ ~" c:' .~t. ~7 .~.. ~- y ~,, n t ; E,:;
G.',~~ ~''.
1 _ t.
~~e~'.7.:..1r~..~J~ro% o~, t~l~ ~at~~.~.~.~n~~~ ~ G1,~.(~
X1.5. ~..~~~ G,~C.1I" .~~"ro.
WO 96/03814 ~ 02432347 2003-06-27 PC.'T/GB95101103 terminal 13 are known, the passage of the mobile terminal through the beams projected by any cf the .-satellites 4 is entirely predictable and this information may obviously therefore be used to 5 determine when handover is to ta~Ce place, and to ~~rhic~
beam.
~~.ter na give ly , the s tr eng ~h or qua l i tv o f s ignals received fr om th a mobi? a te~;,.~.~aal m8 t'.~.r ough the current beam may be monitored and handove= tier~ormed 10 when the s igna l through th a cu:: r en t beam is unacceotableo D=varsity may be prcvided througr. two beams of the same sate? Ii te, p:~o~'id ing a sot beam~co°-beam hangover.
The t'_ming of for~,aard pink trans:uissions is contr o? 1 ed by the ear th s to ~ior. s and the r =_ Burn ' i:zk tr ans~.iss~.or~s ar Q s~rnc~xr ~x~i red ~sr~, th t he r ecep tiob. of f or°,da.'~°k ' l.n-~ ~ 3>~.~ a~ .~, ~ , d ~ ~,n ~.~,'~e ma s t e:E.bod.'e~PPI~ .
~oweve~.~, ix? ~.he: secox~c~ e.a~.bc.~dmmen~;: the mobi,l~ '~rm~,.xoal s 1.8 adjc~s t the fr ~c~xe:~cy of trans~iss? on on the retuan a ~0 ?.a~ri~: ~~a cc~oe.~sate .~'c~:~:° Dc~~xa:~.e~ s'raM.M ~~ det~ac'ed in ~:he i _ .._ c~.~mp~»rsa~~, r rig :: c~~~~ ~c.l~r ~. e~ ~h ~: ~~: c~~r v.~~zE: ~or~~a~..r d lin.~ a x~~:~c;:i~ c >:x.~ ~~C1'~j i""l.ta ~~='~~.':.'7,i ll.~~.~ ~i ~.~ 17.~~7,'1CT
the 5~~~:
=~;~°az~s~~~~s~~.c~~n f're~:;~~:~~B~:y., a~...~,3. xi~~
W~z~~~~~~° cxon~ined tc a w t.~ v _ L",~,.}'~i'~f~1 x"'~"aC~°AI>~,~Rl,j 1.,.~~L~~'.
t~R.~.~.~~~C.)~~'i.C"l.~~i S.3~t.;i Y~'~I.). 1>~Xlle sloes at mc~k~i.le term~.nal traxasx~i~ssion ~:recr~zesv~=~~~a are larger ~.~.
~1 WO 9610381.1 CA 02432347 2003-06-27 PCTlGB95101103 3 I.
the second embcdiment than in the f i:.-s ~ embodiment, to avoid in ter f er erce betwreen adj acen t tire slots cn the return LiII.'C.
~1 thcuch t.'~e above embody:~en is have been described with r ef erence to a mobile cr pcr table ( e. g.
hand-held) termina? , transportab? a or ever. (fixed ter~zinals may be used in the same communications system.
The sys te:~ is not res tr is ted tc any par~:icular L0 constellaticn of satellites, but may advantagecusly be applied to sateT ites in low' ear tt~. o=bits of i ess than ~3 a~ e~'°.a,~~>.'r.~~ or lTled.'~L~'l ear th o'."'~'~hts of a~~set'AfeeT
i ~, Q00 an0 GOg 000 lC:v1 a~ V.htud~?.
Preferably, a subsynchrcncus orbit of apProximate?y o hours' period. may be used, s~onc~ ~ , O o m ~ a '..»n t ~! a n '~' ~. ~..'y'.t~y ~ t~ O Z (~ ~ .~ ~, 'rte .
~n bCW,:1 e~~Cef,"t,~ie~g'~ ,, ~.~~,E,°- ~IL~J~".r:. C:~
'."~~~'s'"sA.O~~ ~.,'3 ~i3~a"1 ~:,.~.~~' f.'.~al~3e :3a~~ aC:0o2:'i~'.b:'~:.~~3e b~', ~~'~0~~~~~'1 J" s~'"m;~ ZZ>~1.~3' dens i ty o f users . ~1 though ~.~.f f er en t f.r ecruencies are .~ T ~ ~ T' ~ M, ~,~
L.s~C~ ~7~' . c '9 ~~ ~~abw.:.>~ '~:v....~~r,z.~'t~_,:~
~o~ d~l'~,.~~...,~~~>o~l a~'te~, 'a',;~C.,'T~'~~.c;a~T~;'.~ C~"~1_~; ~~"~,"E:~1~:~t~:7C:J~' ."~.
S"~~~'t'7,Cp7~.C~
~-~-w,;t.';;"~~CA~ '>.,l,E-''.~l"~m-, f .1~.E,,'~'f,~lu~.-''S~~:"ly',w.'~,3~' ,'.7C-~. s~~~.~."~-!"i~i','~w~u.~,.'.~1~
t.F.Mei~~~.p ~id,~"'L:.su ~,~.~7~.'~'i ~z~~l.~>X-1"~'r'!. G.~.~ s:c-kS~~a"~.is~~W;~~..C.~I~,rr".>P>~''.~
d~' 2~,T>2~ ~..,~~:~%'j ;
P.I.d~~e"~ ~'.'..~t'~' Cry:? d~~C~'," '~;)k,C~.x~ ~,'.3~~i'E?
~.~LI~nY'h'~a ~1~ ~.'~~"
~~
Vin) y..~ 2~..z-.i~'i~'~~~.'~'f~ ~t~,.~;:°~ 5~~~?v~ C~~3~.~ ~~ls~
'L.:~1~ 31 '."~°~~~"__I~; ;i..ll~f~'~s~:,t.~_~~' ~'30'~. ~"? ~t,~ t~?t~. QTR ~co~7~ '~~~:~>~ s:C,~ ..
nl~.:°'~1J.~'°P~~ G~' L7.yy~,'.~'~ ~A
be aCC..'OCCav.2d a'C any.a:~E.' , Only one t.l.~e s l a'L i.ar eaC~'I. C3 u,. ~.°'a.'''°au~l. a'.'~' m.C~~'1 c~~AC~
~"'e~°e%y~.~t~.an LTka"V" .Ce ~~..~ oCa~eC°~ t~
c~ r? C t~, ACIt~J'7 ,°.. ~ ~' ~ 'E..~:!~: i"~ ~. ~°~~L ~. Z, i'~
~~' X'~~7Tlt~ ~:3~; ~1~~.' ~e~'~°~~'1 ~ ;:."r-~'_S T?Y C'J ~ :,C7c :~ 1 ~ .c ,... .y ~ ~ ~.. ~7 ;~ ~° ,y r ~, , (... ~ :' ° ~ !.° ~" ;
t~ i'~
,.as ~ [ _~ n'..'s ,~ c.~. . ~: f,~ ~' ~ ~'t.::... G~... ~. ~..'~.~ , Wit. , ~. .,.~ _ ~ K~.'. ~, ~;~, c"~ U:. ro_ r f ~. .: "A.
e_. h, . _ ~ V ° . .k-. .o 1.4"~ E~~C, u.,l .~ w~~-..C'~S°9. ~ alt~~ ~5~,~' l;~Z')_t.C:~=! C~c' u.. w. _ .~'c <~'I\d3.(~1~(z ,f:d3l..C.~
1 ga err K'y cei:.'~,~,~ M ~~~'a37. ~~ ~s~5',~:6a ~,9tv ~,._i k.'i~ 4 >~ x 'l>
~~'a~ae ..n . cA..i~'~ , 13,~ :~a.i.r3~e~Ai. ~ x:d ~~~,.f~°~,7 ~°'Fz !,:~ p '~hEs f~ E'CXll'~I~f_."~.au'~'J ~~1 p ~~:~j '' f~~ Fz ~.1'~'.s:'!. .~" Ca:~.
communication via only the first satellite 4a. The voice data encoded in a single packet Rx~ or Rx: in the embodiment shown in Figure 10 is divided between t~.to =
packet$ Rx, and Rx, which are transmitted at the frequency ::' by the eart:~ station s at half the normal baud rate in time slots tl and is respectively.
Likewise, the voice data transmitted by the mobile terminal 18 is divided between two packets ' Txa and Txb in each time frame F and transmitted at the frequency fl' in time slots t3 and t~.at half is the normal baud rate. The reduction of baud rate reduces the probability cs bit e_~ors.
Alter.~.atively, two satellite beams aa.~ be used for transmission and reception, and the packets fix,, Rx, and Tx" Tx~~ aay be divided between t:~e two beams.
The above technique of selecti.~.c a ? owe. baud rate and dividing t.~e transmitted sig:.='_ :,to two or mare packets may also be employed in the first embodiment.
$BN~g~
~ In the second embodiment, the satellite beams are not steered but sweep across the earth's surface at a constant rate as the satellite 4 prcgresses in its orbit. As in Figure 7, the beams overlap so that the mobile terminal 18 is able to communicate via more than one beam at least some of the time. Furthermore, beams from different satellites 4a, 4b may overlap so WO 96/038I~i CA 02432347 2003-06-27 PCTIGB95~OI103 t~.at the mobile terminal L8 is able to communicate via more thar. one sate? ? ite 4a, 4b. Transmission or reception fr ecuer.cies are allocated according to the spot beam in which the mobile terminal .18 falls and not accordinc; to the position of the mcbile term~.nal 18 on the ear t h's sur~ace. As the beams of eac:°:
satel l ite 4 swee:; o~rer the earth 's surface, the mobil a terminal I8 wi" oass fr oz~ one beam to the new and a call wi l= the= e_-':.re need to be handed oveT~ fr om beam l0 to beam to reach the mobile termi:al 18. This is ach ieved by dete~i~tinr at the earth station $ which beam the mo::ple :.einal 18 falls within and al? cca ring a ca ~a.~ w i, th ~:he mcb i le te~i.ral.
Is i:~ th a an~roar fate bea.:.. When the mobi? a terminal ? 8 is lv handed over to a new beam, a coanman.d signal is sen t to the rcc~b ~. : a te.~:~en~a ~.. ~ ~ ~.s~~~-~ lading ~..:~.~:
~orma tion nn tAe i ~~".~1~ s ~a~'bW:'. ~%1~ the t:,'.'~.a~.~;.'ct i~ ~n'G
.'.'e~:~~"'~~. f~~'eCa',,~e~'~:M~C'.~
to be user by' t~ae mobi? a ter~l.na1 b~'~ ~:.a~e net~~
beam, a2'~~.
the mobile te~i.nal thereaLter uses the new 20 fr e~.ae~~c~.es and time s? ~':~ indics,ted i~? the command ,1.. ~.r: b. ~.~.~ ~~bl~.i,.~~ ~,.~r-~. ks.y~~.~ ~.l.QS
tA~at ~~ ~ ..~..~ i~~~ ~ ~ a '.~'t~a ear.v~ k=2. s ~e.t ~.c~ E~ ~x~av ~ma anv c5~~ a x~ezmber of ~~.Y ~? T, q. ~:~ r.A f,:a ~.~...~~ t t~ ~';dR,x? ~. C~;
t a ~ s~ r c'a E: i ~ ~'. ~ r"~3 t,. n E~. ~: .--~ t~s'z ~, ~,: ~1, i"~ t~ ~d ~:l:a~". ~7~C,a~~J..~~.~ "~.~~e~,:z~~'ic3. ~_ :i..~ 'f::.C'J
b~ h~a~~:~~~~:3 C~d'e~o ~.~~~a ~dt'R~~:~
~r i9 r ~ ~~
$'7~c~' ~~1 ~~ ~ ~"r~~ ~ ., :~ w. ~',~ 'e.4~.~ ~,. ~.J
~" ~. C: ~ ~ ~5.~ ~" c:' .~t. ~7 .~.. ~- y ~,, n t ; E,:;
G.',~~ ~''.
1 _ t.
~~e~'.7.:..1r~..~J~ro% o~, t~l~ ~at~~.~.~.~n~~~ ~ G1,~.(~
X1.5. ~..~~~ G,~C.1I" .~~"ro.
WO 96/03814 ~ 02432347 2003-06-27 PC.'T/GB95101103 terminal 13 are known, the passage of the mobile terminal through the beams projected by any cf the .-satellites 4 is entirely predictable and this information may obviously therefore be used to 5 determine when handover is to ta~Ce place, and to ~~rhic~
beam.
~~.ter na give ly , the s tr eng ~h or qua l i tv o f s ignals received fr om th a mobi? a te~;,.~.~aal m8 t'.~.r ough the current beam may be monitored and handove= tier~ormed 10 when the s igna l through th a cu:: r en t beam is unacceotableo D=varsity may be prcvided througr. two beams of the same sate? Ii te, p:~o~'id ing a sot beam~co°-beam hangover.
The t'_ming of for~,aard pink trans:uissions is contr o? 1 ed by the ear th s to ~ior. s and the r =_ Burn ' i:zk tr ans~.iss~.or~s ar Q s~rnc~xr ~x~i red ~sr~, th t he r ecep tiob. of f or°,da.'~°k ' l.n-~ ~ 3>~.~ a~ .~, ~ , d ~ ~,n ~.~,'~e ma s t e:E.bod.'e~PPI~ .
~oweve~.~, ix? ~.he: secox~c~ e.a~.bc.~dmmen~;: the mobi,l~ '~rm~,.xoal s 1.8 adjc~s t the fr ~c~xe:~cy of trans~iss? on on the retuan a ~0 ?.a~ri~: ~~a cc~oe.~sate .~'c~:~:° Dc~~xa:~.e~ s'raM.M ~~ det~ac'ed in ~:he i _ .._ c~.~mp~»rsa~~, r rig :: c~~~~ ~c.l~r ~. e~ ~h ~: ~~: c~~r v.~~zE: ~or~~a~..r d lin.~ a x~~:~c;:i~ c >:x.~ ~~C1'~j i""l.ta ~~='~~.':.'7,i ll.~~.~ ~i ~.~ 17.~~7,'1CT
the 5~~~:
=~;~°az~s~~~~s~~.c~~n f're~:;~~:~~B~:y., a~...~,3. xi~~
W~z~~~~~~° cxon~ined tc a w t.~ v _ L",~,.}'~i'~f~1 x"'~"aC~°AI>~,~Rl,j 1.,.~~L~~'.
t~R.~.~.~~~C.)~~'i.C"l.~~i S.3~t.;i Y~'~I.). 1>~Xlle sloes at mc~k~i.le term~.nal traxasx~i~ssion ~:recr~zesv~=~~~a are larger ~.~.
~1 WO 9610381.1 CA 02432347 2003-06-27 PCTlGB95101103 3 I.
the second embcdiment than in the f i:.-s ~ embodiment, to avoid in ter f er erce betwreen adj acen t tire slots cn the return LiII.'C.
~1 thcuch t.'~e above embody:~en is have been described with r ef erence to a mobile cr pcr table ( e. g.
hand-held) termina? , transportab? a or ever. (fixed ter~zinals may be used in the same communications system.
The sys te:~ is not res tr is ted tc any par~:icular L0 constellaticn of satellites, but may advantagecusly be applied to sateT ites in low' ear tt~. o=bits of i ess than ~3 a~ e~'°.a,~~>.'r.~~ or lTled.'~L~'l ear th o'."'~'~hts of a~~set'AfeeT
i ~, Q00 an0 GOg 000 lC:v1 a~ V.htud~?.
Preferably, a subsynchrcncus orbit of apProximate?y o hours' period. may be used, s~onc~ ~ , O o m ~ a '..»n t ~! a n '~' ~. ~..'y'.t~y ~ t~ O Z (~ ~ .~ ~, 'rte .
~n bCW,:1 e~~Cef,"t,~ie~g'~ ,, ~.~~,E,°- ~IL~J~".r:. C:~
'."~~~'s'"sA.O~~ ~.,'3 ~i3~a"1 ~:,.~.~~' f.'.~al~3e :3a~~ aC:0o2:'i~'.b:'~:.~~3e b~', ~~'~0~~~~~'1 J" s~'"m;~ ZZ>~1.~3' dens i ty o f users . ~1 though ~.~.f f er en t f.r ecruencies are .~ T ~ ~ T' ~ M, ~,~
L.s~C~ ~7~' . c '9 ~~ ~~abw.:.>~ '~:v....~~r,z.~'t~_,:~
~o~ d~l'~,.~~...,~~~>o~l a~'te~, 'a',;~C.,'T~'~~.c;a~T~;'.~ C~"~1_~; ~~"~,"E:~1~:~t~:7C:J~' ."~.
S"~~~'t'7,Cp7~.C~
~-~-w,;t.';;"~~CA~ '>.,l,E-''.~l"~m-, f .1~.E,,'~'f,~lu~.-''S~~:"ly',w.'~,3~' ,'.7C-~. s~~~.~."~-!"i~i','~w~u.~,.'.~1~
t.F.Mei~~~.p ~id,~"'L:.su ~,~.~7~.'~'i ~z~~l.~>X-1"~'r'!. G.~.~ s:c-kS~~a"~.is~~W;~~..C.~I~,rr".>P>~''.~
d~' 2~,T>2~ ~..,~~:~%'j ;
P.I.d~~e"~ ~'.'..~t'~' Cry:? d~~C~'," '~;)k,C~.x~ ~,'.3~~i'E?
~.~LI~nY'h'~a ~1~ ~.'~~"
~~
Vin) y..~ 2~..z-.i~'i~'~~~.'~'f~ ~t~,.~;:°~ 5~~~?v~ C~~3~.~ ~~ls~
'L.:~1~ 31 '."~°~~~"__I~; ;i..ll~f~'~s~:,t.~_~~' ~'30'~. ~"? ~t,~ t~?t~. QTR ~co~7~ '~~~:~>~ s:C,~ ..
Claims (7)
1. A method of satellite communication, comprising:
directing a plurality of beams from a non-geostationary satellite to a corresponding plurality of regions which are fixed relative to the surface of the earth; and determining when one of said beams fails to satisfy a predetermined criterion, and redirecting said one of said beams from the corresponding one of the fixed regions to another fixed region such that one of said beams satisfies said predetermined criterion; characterised in that the directions of other ones of said plurality of beams which satisfy said predetermined criterion are maintained at the corresponding ones of the fixed regions while said one of said plurality of beams is redirected.
directing a plurality of beams from a non-geostationary satellite to a corresponding plurality of regions which are fixed relative to the surface of the earth; and determining when one of said beams fails to satisfy a predetermined criterion, and redirecting said one of said beams from the corresponding one of the fixed regions to another fixed region such that one of said beams satisfies said predetermined criterion; characterised in that the directions of other ones of said plurality of beams which satisfy said predetermined criterion are maintained at the corresponding ones of the fixed regions while said one of said plurality of beams is redirected.
2. A method as claimed in claim 1, wherein said directing and redirecting steps comprise sending a command signal to said satellite from an earth-based station, so as to control the direction of the beams to said satellite.
3. A method as claimed in claim 1 or 2, wherein said predetermined criterion comprises a range of desirable beam directions whereat the satellite h.as an elevation angle greater than a predetermined minimum elevation angle with respect to the fixed region.
4. Apparatus for satellite communication, comprising means operable to determine a plurality of beam directions, for a plurality of beams projected by a non-geostationary satellite, to corresponding fixed regions of the earth's surface;
means operable to detect whether one or more of said beams fail to satisfy a predetermined criterion; and means operable to determine a new beam direction to a new fixed region for each of said one or more of said beams, such that the predetermined criterion is satisfied by the beam in the new beam direction; characterized by control means operable to control said non-geostationary satellite so as to direct the beam s in the corresponding beam directions such that the directions of other ones of said beams for which a new beam direction is not determined are maintained at the corresponding fixed regions.
means operable to detect whether one or more of said beams fail to satisfy a predetermined criterion; and means operable to determine a new beam direction to a new fixed region for each of said one or more of said beams, such that the predetermined criterion is satisfied by the beam in the new beam direction; characterized by control means operable to control said non-geostationary satellite so as to direct the beam s in the corresponding beam directions such that the directions of other ones of said beams for which a new beam direction is not determined are maintained at the corresponding fixed regions.
5. Apparatus as claimed in claim 4, wherein said control means includes means for sending a control signal to said satellite.
6. Apparatus as claimed in claim 4 or 5, wherein said predetermined criterion comprises a range of desirable beam directions to points on the earth's surface whereat the satellite has an elevation angle greater than a predetermined minimum elevation angle.
7. A terrestrial station including apparatus as claimed in any one of claims 4 to 6.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9414829A GB2293725B (en) | 1994-07-22 | 1994-07-22 | Satellite communication method and apparatus |
| GB9414829.3 | 1994-07-22 | ||
| CA002195662A CA2195662C (en) | 1994-07-22 | 1995-05-16 | Multi-beam tdma satellite mobile communications system |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002195662A Division CA2195662C (en) | 1994-07-22 | 1995-05-16 | Multi-beam tdma satellite mobile communications system |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2432347A1 CA2432347A1 (en) | 1996-02-08 |
| CA2432347C true CA2432347C (en) | 2005-08-02 |
Family
ID=28675932
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002432345A Abandoned CA2432345A1 (en) | 1994-07-22 | 1995-05-16 | Multi-beam tdma satellite mobile communications system |
| CA002432347A Expired - Fee Related CA2432347C (en) | 1994-07-22 | 1995-05-16 | Multi-beam tdma satellite mobile communications system |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002432345A Abandoned CA2432345A1 (en) | 1994-07-22 | 1995-05-16 | Multi-beam tdma satellite mobile communications system |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA2432345A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114826376B (en) * | 2022-03-30 | 2023-11-10 | 大连大学 | Multi-objective optimized resource allocation method for micro-nano satellite |
-
1995
- 1995-05-16 CA CA002432345A patent/CA2432345A1/en not_active Abandoned
- 1995-05-16 CA CA002432347A patent/CA2432347C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2432345A1 (en) | 1996-02-08 |
| CA2432347A1 (en) | 1996-02-08 |
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