BSTJ 50: 2. February 1971: The Picturephone System: A Digital Transmission System for TD-2 Radio. (Broderick, C.W.)

8.6 MB·English

‘The Picturephone® System:

A Digital Transmission System
for TD-2. Radio

by ©. W. BRODERICK,
(Osnaacit ssved enter 2, 170)

A econ foc rama distil spade cane TDS edema rds
olay restos han Bone deviged ond eos! i o reco ibd Wiad. This
‘aaperdatesonin of the vaio eta chacarrisin whisk sbuenced
Ie devi, deere the maior entree of the trina, aul reports he
triad res, Te ginal will be ued in the tll nto provie ner

ily Peturaphong® trans aa de cout

‘Tee TD? Radio Reley System is the major tmvnk corr system
in the Doll srameconricental actwork, interconnecting every nj
retropolzaa centr in the Unitod States Therefore a digal ans
risson groms, ite nstural ep eonsidar how TD-2 might be wed t0
‘stra these signal.

‘A ternianl Ubab piee the digi it slream Wo TD-2 has been
signed to tranmmit nt Rote nf 202 rogaite pee tnnd (M/A
sing » four-level, 10Temegatany! pb oral to mda standard
"TD2 terminal wpioment. The ins ie eranged Jo wale ap Lo
tires 6.812-Vih/s Kino soars frac euch eouteee ax Peterephone
faders and data see, Design feanires Snluce the use of lee etafing
for multiplex eynehnonizeion, dedieated ules for Ging te0overy,
fs toansversal Alter for optimising the reeived eye pattern and the
tee of sellaynehronizing sertmblers for testing ** The sig is rege
cated as busebund about every 400 miles to limit the weeuxulation
of unequalizablo pulse distozien

‘A rumber of digital torminsle have been constructed and tested in
conjune‘on with the New York-Pstsburek Picturepkone product wal
Tet romls on this 4Bi-ms tial rat, using ore regenerator sation,
case Hietel that pertarmanee of licen ‘an one error ix 10 bit,
482 num any ererme macmocac sovaman, seMMUARY

in the abeance of sguifoant fading, bas bean realized. Tho eror ral
inerests to about oe err in 1° Vita when the roseired sianal om
‘any radio hop fadas to the pont whore transmizeon ip evitehed mito
ruaticaly to a protein radio frequensy obannel

1 0-2 snopoware averaie

‘The TD.2 microwave radio eystem hus been deserved previous
1 opwrates in the 8700- to 4200-Mie bund, with the 20-MHs-wid
‘channels spaced 20 Sle apart. Te ayers employs frequeney mea
Tauion of wn IP oacieeeonzerod at 70 MLL prior to conversion to the
amierowave epeeivan, ‘The bss frieney sespenee ie eonatant to
‘within 0.8 4B lo abou! 3 MTFs for w S0-mil yee

The relinbity of the radio chencel is maintained to high degree
through the availbilily of nulonntiewutehing to standby protestion
hanrrl in the event of a sigaal-to-nlee rato (S/N) below miniznam

ema dese late the esting TD-2 rlerowave equipment includ
ing the 28 FM terminals and to meke the digitally modula mero
‘wave cbarnel compatible with gular analog message and terion
slgnala on aljavent merowave chaniels% Tale makes il porsibla to
ace the existing TD-2 aationvido nutwork in providing Pisturephone
tall trunking and egal dala ezeaite and i imposes the following
Slava eonstreats:

(@ The bescbend cial must not interfere wit the radio protetion
swicehing syste whieh uate w 7-Mle pile tone ard e MPs nose
"ot. This sovomplished by using » bueebend treasnitier Biller whow
‘uta frenueney is below 9 MLL

(3) ‘Tae 1 sjga spectrum saust aot intasfore with dhe rwive sot
‘roquenty or the top mestage fcequeney of the adjacent ebel. This
limite the peak frequency deviction

(ii) Tas limiting S/N in detemained by the protection enitehing
system initiator setting used for anslog messege service

lio) The dial signal mur: be regenerated to limit tae unequalia-
ble asssband distortion exoountered in REF teanamision,

"The ended Pictanephone signal hos 6.412-Mba ate? This rate was
shen lo traieh a standard Ti tale hich f evolving an part of the
Ball Sywenis digital trenssson nets end whieh wil be wed by
the T2 igial ie, The digital 'amsission spate capac here>
{ore wns ciocen in inerement of the @S12-Mbe rl,
rot manussios: st8te a8

‘The intial uae of che terminals io suppor: of the Pisbrephons
predate ‘tial between New ors sil Pitshorgh required wa err
Fave of <r, A ploe of the recuicol B/N for fixed err rates and of
le aveVable S/N de ta dhe above restrictions, Bath as x funelion of
‘tho syne Bit ct, ie aoe in ig. 1, Ihe alle 87 is ealalater
at the fading threshold of Ue rolio potection switching yyater. TH
tue’ Ihe sigral entrants above, the pale inenuerey deviation ane
‘Rerctoce le uvallahe 2/8 ust deeronsr a nho Ayatem bit rate

"The iil sigual ese patzra distortion inorsmes with increasing
ceystem Dil ale due to t2e sharper rollo? ithe Daseiand Bltering
Thonono, the required S/N for eure erie vale ineeases a the
ceysteca bi» male ineeraves, #rom the ixeroation of The veited 8/8
tive and the erainile B/N curva, i ean be seen that the eystem
fapacity a about 21 snails Tor an sero nrabebility of 10 al he
Teling threshold of the ride rotor iw lahirg ape. ‘Te diol
rv ips Rerazore wae ect a throe 342 Ma “aoa ‘The eystom
Deramevara ate paced in Tob

"The wemeroling signal eoxstaiat (he Flaswetion in Pig, 1 ia LP
levl spolsal overlap nto tan melee elt froquerey 0 Une adjaceal

of) XO |

Fig, tavnlie 5/7 and suid 3/8 Gr nase pedir af aon
sri ror Bae
$84 rmx az sverm sromnncst socmst, runavany unt

chanzel. Thin 2 a form of nearend adjanmt ehsnoel invrferance
ino a ever aa eonter Feu 20.Meatay tin tans
mitce, The inverfeenee path include the sigetu-de wupling of
nunoeas torn elector waleneas aad the Jasin mrad rane "ror
tionmmitter vo entenne and antenna to reteiver, The eouping oes ie
fypieay aboot 109 aR wave eveulte in # redelion of ade engin
qual ta 0.8 6B. Ia some eirscmstanos ering dfcshies Lead to esupl-
ing Ions that ane aevora sina, end hungfors a futhes ere
fa ari

41 Trosanitng Peemieat

A implied block diagram of the tremnittie Serius shown
in Pig. 2 wih spinal wavcfosne, ‘ho eigtal trexmitter aotepts
‘three 6312-Mb > pulse azeume in parallel ond millers ther ity
2 single ceil pule stream.

‘Tamen [Drom Trasmunsnos Sterna Passer

1 Tra ja Tame
~ omg ‘ia geste Lge aoa ed

ee Sear Was pe

‘akan capable FEB Goda awa weve

Out Ta Ga Ms lr

{09 pa bandh For igital oT

‘isan
oR HANSA SRT 485,

DNs

Tie, 2-Distel came oes ast lo renege

‘The output of the digital srwwmilier ip a 1O.-mesubeud, four-
level signal which ie mede up of infomation pulse, fearing pulses,
ane eyasinorization pulse, Ih composite signal i Bhen shaped by
the baeebard lter fa the signed which wil deviate the FM ane
titer,‘ output speenruma of se IM trometer, eaaterod ssoxnd
10 MElg is stow in spied

2 Bovwting Terminals

At the seceiving tring), ae digital ema is recovered from the
FM serial seeiver at baeeband, fltered, equated od dezul
plexed inco tines G212-Mb/s sigue, A simplest Mock diagram of
we nteiving terminal, together with ite appropriate waveforms, Is
shown in Fg, 3, The fancinnal opeeston ofthe receiver iv eacatialy
the invaree of the traneittr

a Fito

‘The overall shaping and Sering of the four-level, 10.1-megabaud
tuschand signal ie obsained by eplicing the baseband Allering and
Jowsling portion of iin tho transmitting terminal to bund limit the
sisal tnd the reminds in the receiving termine). Uo limit noise
‘The combined tnnaminion eharactarctic of the baseband Bers pro-
duces a pulse wih w mine emvine apedrum which has a high tolerance
to interference”

‘Tae enanemiter

basin Stor earacarstia ie ven
486 urn nts senna TecMSueAL JOURNAL, HREREARY 177

faa fe<\I\ < lan hee
"The resiver beacband fier characteris is given by

1 fl Stash

Ef <font hi

10.41 Mi,
‘i jerent vllof ter ured in shove terminal, fe equals
Jaye The 2/sin tema inthe tremaitter Miller chorea iso cor-
rection forthe spectuts of the asuare-mave input

‘The digital trunmictr block af Fix, 2 i shawn ix expanded block
iagram form in Ag, 4, The fei of Bit atraun synabroniation,
‘ruldplexng, and modulstion shown in Wig. ane deseribed below

"To tine multiplex the fuoe indopondent GSI2-Mb/e ipats, each
faput mast be eynehronined to the sane eos frequency. This is ao-
complished by the method of pulse snufing. Hach input is writen
{nto a eoparntevighrell elses store under the contol of ex inpot

Prottuence we

al mel =
UREA, massa sxasese 437

“nen

eon sa

al sesgyppneen™ ers augur?

Wig $B don of Ul ema

lock devived feom tke average froquensy of the respective input
Siezal, The input froquoaey is 8sil2 Mie SU ype which ia a tl
frmmoe of shest 100 Te. Tho racing funation foreach synchraniser
is porfonmad by one of turzo red elves yuroratd in tho puso sting
ontra. Bach of thece read eles overs long pried of tima has exaedly
the sate nua of elk ples oe tare one information ple writen
into the storage cally of tha wmocitad elute wore. Furthormore,
tach rend lock bes boen blond oppropriately to allow the inseton
ff the feuming and synchronising poles, Soneen bisa ow, oF every
2o0-bie frame are aloceted for those purpeeca. ‘The namical pulse
stofting rato ia 500 aul pulsce por eccond. ‘Tis zat i varicbo from
inioum of reno to maximum rule of ome sult every 12 (umes. Tae
‘tual eyachronixtion fe perfermed by Se puto suing contol shrogh
‘tho mitoring of sta quests goncrated by nearly empty clasti stor
‘Thee stuf requesteresch the pulse stlling eontel va tus multiplex.
All of the peridie waveforms cequired to posiorm the Zunetions of
synebroaising, multiplesine und modulating exe genernted in the
Crmesller eoninn vontni. The bese atten lees Praqeney ie
20.2 NHL MN pins gonna bythe 20.2-MLLsexytal coclator

‘Pho mrtiple aespls Ie thce properly eyhnonined ifertion
688 vie nn aver rmomsTen JuuRAL, seMUANY HA

ple scans with ther sovorint! sin request poles Isle recives
Uhe required periadie waneforae fea Ube pale stoi control xl
Uo tranemitier common oontrol and te sultiplece them tpter
With the information pubis art Ataf poses into 2 20.2-Mb/s binary
stream, Included in thie stron ace the neeweeary contel signals to
allow tho rerver ta remove tho eed sn pues.

fica esital operation inthe elt iy (owiodalae dhe 20.2-Mb/s
binary signal to-a foes, 1.Lomegebuud sigeal. Thi tokes ple
in bo suese, The 202-hy/s binay aignal ie frat earvertod into eo
mall 10.1-Miys binary atreaca wish soe then converted into &
Sngle, four-level 10d-megabrad siaal, Amplified ehemasie dia
fam of the mocltor ix bows in Ile. B, The eral bie pars, BP,
fre mapped to pairs of pslll bit 4/2, iro the Tantions

D> Fe

ond
2 = BOR
‘The parallel bit pave ther. contol ike cotter soupled transistors
hich ous the proper sazouy2 of erent foun she euz:ent genenstors
Int the loud reiter to prcdave the “awlevel nent signal
‘The dgtel egnal forint atthe bioary obenu of the muliplx end
the coreezponingfour- rel signal unt af th modsaene age tate
In Fig. @ The contents of ene rare ser rhawe, ‘naludicg dec

Gg

Fig 4-Motnler ©,
sed te comtloneats D. =

nen
berets waneniaion oenes 190

fey

eel Siem | ft

ie Pe Korn of dg i

Sraming pulse, stu spe pile, nhl ls, ad Information place
‘The ctu eyao pulkos of 12 svereaive frames make up ately ro2us-
lant word hich isientes fo te nteiver when and where ati puloss
see iraeed for esch of the thres informacion chuonele. Prem the
Tmodulalor, the signal pwear trong the tsanamittiog Aer, hich
‘oirets cho hrsrhend ferononrien en papridas the cetined pase ebay
ing, and tien to en FM trensrlter Srough an wrbalanced-to-bal-

anced ampli.

"The digital vecever bloc of Fiz. 3 is sbown in expunded bloc.
iagzam form in Tig, 7 Al the digital receiver the four-level, 10.
‘egnband signl, fromm the TO reseiver, ie eonverted to an unbalanoed
fignal and then seer fire through The receiver baseband ter and
into the tranzwereal filter, Th basso Filler, tageer wilh he fer
in the transiting termineh, providre optimum shaping of the hase
band tesponse charters, lve etwortal fer spies schematic
in chown in Fig, 8. The inp sta poets cong 2-seton Lael
delay Tie, ‘Tho prin nf eash tp, except forthe enter top, ie manually
adjustable ro hat the output signal S(t) ix given by

540» Si xasie~n0,
490i mts svsvaae teen eat TOFRNAT, FRENTE TET

where
Ka -1<K<4

Si ~ we)
isthe input signal ot tho nth tap.

Adjustment of the tap gxins, Ry, componmaies for the nantading
Uisortion encountored by tho tgaal in transmission over the radio
thanncl. ‘The oqualired ontout eigasl driver the digital section of
the reoever.

"The operation af the Tessier iin general, Ube inverse ofthe range
smiter. The revi vereonveci dy 10.-mnysbals, four-level input tga,
into threo 6812-Afa/e pote strane hy fst derotulating the signal
foto 2 202-Mbs binary date stroun, end thea seurating and adjut-
ing tho timing of, or deeynchronising, the threo individual cutput
ena

Tig. tlk daar of resving temas