satellite up or down link design

7/25/2019 Satellite Up or Down Link Design

http://slidepdf.com/reader/full/satellite-up-or-down-link-design 1/31

Satellite Link Design



Content

• Design of the Satellite Links• Link Budget and their Interpretation



Introduction• A satellite link is de ned as an Earth

station - satellite - Earth stationconnection.

• The Earth station - satellite segmentis called the uplink

• The satellite - Earth station segmentis called the do nlink



Introduction The Earth station design consists of!

The Transmission Link Design or theLink Budget!the Transmission S"stem Design.

• The Link Budget esta#lishes theresources needed for a gi$en ser$iceto achie$e the performance o#%ecti$es



Design of the Satellite Link• The satellite link is pro#a#l" the most

#asic in micro a$e communicationssince a line-of-sight path t"picall"e&ists #et een the Earth and space.

• This means that an imaginar" linee&tending #et een the transmitting

or recei$ing Earth station and thesatellite antenna passes onl" throughthe atmosphere and not groundo#stacles.



Design of the Satellite Link• 'ree-space attenuation is determined #" the

in$erse s(uare la ! hich states that the po errecei$ed is in$ersel" proportional to the s(uare of

the distance.• There are! ho e$er! a num#er of additionale)ects that produce a signi cant amount ofdegradation and time $ariation.

•

These include rain! terrain e)ects such asa#sorption #" trees and alls! and some less-o#$ious impairment produced #" unsta#leconditions of the air and ionosphere.



Design of the Satellite Link• It is the %o# of the communication engineer

to identif" all of the signi cant contri#utionsto performance and make sure that the" are

properl" taken into account.• The re(uired factors include the

performance of the satellite itself!• The con guration and performance of the

uplink and do nlink Earth stations! and• The impact of the propagation medium in

the fre(uenc" #and of interest.



Design of the Satellite Link• The *' carrier in an" micro a$e communications

link #egins at the transmitting electronics andpropagates from the transmitting antenna throughthe medium of free space and a#sorpti$e

atmosphere to the recei$ing antenna! here it isreco$ered #" the recei$ing electronics.• The carrier is modulated #" a #ase#and signal that

transfers information for the particular application.• The rst step in designing the micro a$e link is to

identif" the o$erall re(uirements and the criticalcomponents that determine performance.• 'or this purpose! e use the #asic arrangement of

the link sho n in 'igure.



Design of the Satellite Link



Design of the Satellite Link• Bidirectional +duple&, communication

occurs ith a separate transmissionfrom each Earth station.

• Due to the analog nature of the radiofre(uenc" link! each elementcontri#utes a gain or loss to the linkand ma" add noise and interferenceas ell.



Design of the Satellite Link• The result in the o$erall performance is

presented in terms of the ratio of carrierpo er to noise and! ultimatel"!

information (ualit"• An" uncertaint" can #e co$ered #"

pro$iding an appropriate amount of linkmargin! hich is o$er and a#o$e the Cneeded to deal ith propagation e)ectsand nonlinearit" in the Earth stations andsatellite repeater.



Link /arameters0 Impact on Ser$ice 1ualit"



Satellite Link Design

The four factors related to satellite s"stem design23.The eight of satellite4.The choice fre(uenc" #and

5.Atmospheric propagation e)ects6.7ultiple access techni(ue• The ma%or fre(uenc" #ands are 8 6 9:;! 36 33

9:; and 5< 4< 9:; +=plink Do nlink,•

At geostationar" or#it there is alread" satellitesusing #oth 8 6 and 36 33 9:; e$er" 4>+minimumspace to a$oid interference from uplink earthstations,



LINK BUDGET The link #udget determines the antenna si;e to deplo"!

/o er re(uirements!link a$aila#ilit"!#it error rate!

o$erall customer satisfaction ith the satellite ser$ice.• A link #udget is a ta#ular method for e$aluating thepo er recei$ed and the noise ratio in a radio link .

• It simpli es C ratio calculations• The link #udget must #e calculated for an indi$idual

transponder! and must #e recalculated for each of theindi$idual links



LINK BUDGET

The satellite link is composed primaril" ofthree segments2

+i, the transmitting Earth station and theuplink media?

+ii, the satellite? and+iii, the do nlink media and the recei$ing

Earth station.•

The carrier le$el recei$ed at the end ofthe link is a straightfor ard addition ofthe losses and gains in the path #et eentransmitting and recei$ing Earth stations .



LINK BUDGETS

• C ratio calculation is simpli ed #" theuse of link #udgets

• E$aluation of the recei$ed po er andnoise po er in radio link

• the link #udget must #e calculated forindi$idual transponder and for each link

•

@hen a #ent pipe transponder is usedthe uplink and do n link C ratios must#e com#ined to gi$e an o$erall C



Link Budget Example• Satellite application engineers need to assess and allocate performance for

each source of gain and loss.• The link #udget is the most e)ecti$e means since it can address and displa"

all of the components of the po er #alance e(uation! e&pressed in deci#els.• In the past! each engineer as free to create a personali;ed methodolog" and

format for their o n link #udgets.• This orked ade(uatel" as long as the same person continued to do the ork.• /ro#lems arose! ho e$er! hen link #udgets ere e&changed #et een

engineers! as formats and assumptions can $ar".• A standardi;ed link #udget soft are tool should #e used that performs all of

the rele$ant calculations and presents the results in a clear and complete

manner.



Link Budget Example• @e ill no e$aluate a speci c e&ample using a

simpli ed link #udget containing the primar"contri#utors.• This ill pro$ide a t"pical format and some

guidelines for a practical approach.• Separate uplink and do nlink #udgets are pro$ided?

our e$aluation of the total end-to-end link presumesthe use of a #ent-pipe repeater.• This is one that transfers #oth carrier and noise from

the uplink to the do nlink! ith onl" a fre(uenc"translation and ampli cation.

• The three constituents are often sho n in a singleta#le! #ut di$iding them should make thede$elopment of the process clearer for readers.

• The detailed engineering comes into pla" ith thede$elopment of each entr" of the ta#le.

•

Se$eral of the entries are calculated usingstrai htfor ard mathematical e uations? others



Link Budget Example• This particular e&ample is for a C-

#and digital $ideo link at 6< 7#ps!hich is capa#le of transmitting to

34 T channels using the 7otion/icture E&perts 9roup 4 +7/E9 4,standard.



Link Budget Example:Downlink Budget

The follo ing Ta#le 4.5 presents the do nlink #udget in amanner that identi es

• the characteristics of the satellite transmitter• and antenna!• the path!• the recei$ing antenna!• and the e&pected performance of the Earth station recei$er.• It contains the elements that select the desired radio signal

+i.e.! the carrier, and demodulates the useful information +i.e.!the digital #ase#and containing the 7/E9 4 transport #it

stream,.• nce con$erted #ack to #ase#and! the transmission can #e

applied to other processes! such as de-multiple&ing!decr"ption! and digital-to-analog con$ersion +D A con$ersion,.




• Each of the link parameters relates to a speci cpiece of hard are or some propert" of themicro a$e path #et een space and ground.

• A good a" to de$elop the link #udget is to

prepare it ith a spreadsheet program.• This permits the designer to include the $ariousformulas directl" in the #udget! thus a$oidingthe pro#lem of e&ternal calculation or thepotential for arithmetic error

•

Commercial link #udget soft are! such asSat7aster /ro from Arro e Technical Ser$ices!does the same %o# #ut in a standardi;edfashion.



Satellite link design -Uplink • =plink design is easier than the do n link in man"

cases

earth station could use higher po ertransmitters• Earth station transmitter po er is set #" the

po er le$el re(uired at the input to thetransporter! either

a speci c Fu& densit" is re(uired at the satellitea speci c po er le$el is re(uired at the input tothe transporter

• anal"sis of the uplink re(uires calculation of thepo er le$el at the input to the transponder sothat uplink C ratio can #e found

• @ith small-diameter earth stations! a higherpo er earth station transmitter is re(uired to

achie$e a similar satellite EI*/.interference to other satellites rises due to



Link Budget Example:Uplink Budget



C N

GC <HD GEI*/HD J G9 THD - GL SSESHD K GkH GC<H= GEI*/H= J G9 TH= -GL SSESH= K GkH



Link Budget Example:!"e#all Link Budget

• The last step in link #udgeting for a #ent-pipe repeater is to com#ine thet o link performances and compare the result against a minimumre(uirement also called the threshold.

• Ta#le 4.M presents a detailed e$aluation of the o$erall link under theconditions of line-of-sight propagation in clear sk".

• @e ha$e included an allocation for interference coming from sources suchas a cross-polari;ed transponder and ad%acent satellites.

• This t"pe of entr" is necessar" #ecause all operating satellite net orks aree&posed to one or more sources of interference.

• The #ottom line represents the margin that is a$aila#le to counter rainattenuation and an" other losses that ere not included in the link #udgets.

• Alternati$el"! rain margin can #e allocated separatel" to the uplink anddo nlink! ith the com#ined a$aila#ilit" $alue #eing the arithmetic productof the t o as a decimal $alue +e.g.! if the uplink and do nlink ere eachNN.NO! then the com#ined a$aila#ilit" is <.NNN P <.NNN <.NN or NN. O,.



Link Budget Example:!"e#all Link Budget



S$TELLITE LINK DESIGN%ET&!D!L!G'

The design methodolog" for a one- a" satellitecommunication link can #e summari;ed into thefollo ing steps.

The return link follo s the same procedure.• Step 3. 're(uenc" #and determination.• Step 4. Satellite communication parameters

determination. 7ake informed guesses forunkno n $alues.

•

Step 5. Earth station parameter determination?#oth uplink and do nlink.• Step 6. Esta#lish uplink #udget and a transponder

noise po er #udget to nd +C ,up in thetransponder

• Step M. Determine transponder output po er from




• Step 8. Esta#lish a do nlink po er and noise#udget for the recei$ing earth station

• Step Q. Calculate +C ,do n and +C ,u for a

station at the outermost contour of thesatellite footprint.• Step . Calculate S * BE* in the #ase#and

channel.•

Step N. Determine the link margin.• Step 3<. Do a comparati$e anal"sis of the

result $is-R-$is the speci cation re(uirements.




• Step 33. T eak s"stem parameters to o#tain accepta#le+C ,< S * BE* $alues.

• Step 34. /ropagation condition determination.• Step 35. =plink and do nlink una$aila#ilit" estimation.•

Step 36. *edesign s"stem #" changing some parameters ifthe link margins are inade(uate.

• Step 3M. Are gotten parameters reasona#le Is designnanciall" feasi#le

• Step 38. If ES on #oth counts in step 3M! then satellite linkdesign is successful K Stop.

• Step 3Q. If on either +or #oth, counts in step 3M! thensatellite link design is unsuccessful K 9o to step 3.

satellite up or down link design

Documents