BSTJ 50: 2. February 1971: The Picturephone System: Crosstalk Considerations in the Transmission of Analog Signals on Paired Cable. (Bunin, B.J.; Hirsch, R.B.; Olsen, R.E.)

14.3 MB·English

The Picturephone® Sys

Crosstalk Considerations in the
‘Transmission of Analog Signals
on Paired Cable

lly UJ. BUNLN, KB, HURSCHY, nnd BB. OTSEN
(unit rocivad Ober 1670)

Cronos $4 an snpolend eonsieration ix the enimion of anaiog
taanhand Vitusephune® nigoate ew yaad cobs, Creenalt dua 20 the
suorat disuring Pigurphne jwalcas eas @ aati ie inter
rence pation. Crosal inrerenee from other Pieturephone att widen
fond sytiona, suck og 1 and Te Aji! Uns, eontbuts 1 random
oie Tt ation, jonBoe win woaiale couple may cause spurioue
‘nailaon of sable agualitere, Methods are derméned 12 camol hess
impacts by ping retvelion ow euler xpariny un eile pase
casement

exchange onble pais will provide the mtiua for sewremisiva
tho salog busebard Putercptons Smal over subseribar loope and
sort loee trunks? The unwatrt coupling of encrey, or erortal, bo-
fineen paire within a enblo plans impertant Ltations on the engi
neering of thera equalized rmnninisnion line.

14. Type of Empairments

"Taree type of implnnenta in the Diztureplone sual whieh ent
ecur ia the presen ni eolalk ero considered inthis netiele. They
tte lst! ia Teble I slong with the sour ot the impairmenl, Near
fend ane far-crd erosstals coupling puths are shown in Fiz, Lt

aa WoratDisarber Tterjecence

‘The fret impuirment i eaueed by interecence from the single most
prominent Dietwreplone Interering signel among ull those presat,
And io called worst-distarber interference, The signal fromthe worst
428 vom ne evernag cuuansoat sormeat, FEBRUARY TL

Ainoaben, when preend through a exestelk eoupling prth, will ap-
pear ciferentnted nnd superimposed on the deiod sienl. Sinoe the
thro siguels ere nob synchroniza, (he interenenon will drift across the
scent when che deited signal is Giplayo!. For example, if the syne
pulbes are the mt detrimental part of un interfering Plzturepkone
gna, the interference ell appear ax two veri lines, on black and
fone white, ding acroce the sercn,

112 Randoo ois Itrforence

[Byer if no wigatl i visible ge & wore disishor,eaoh of the intar-
fering Pictwrephone signals ill vonribuce unwanted energy to the
slain) signal, Tris energy must be consilerel aa a oontibation ta
the over] sgales random nelze, which ia the seond impairment
‘whose olfeaiany etudid. The interfering wale do not necescarily
Iavve to be of tae Piturephona type, bit ald Tie of any widebend
ryatem, Tn (his tile we consider crsetale coupling of noize from
Picbiephone, TL Une, and 2 dae sigur, Tolerverence trom the
‘igital systems Je sued om true fecliticeoaly,sinoe enrier ayt=
les are noe ually preven on enbecrber loop eeble

‘Additional souross of interference, such as X cari eystma exist,
Inu are not eomeigered in his article. Fethermore, the eect of inter-
ferciee or other eystams ovueed ky Uke coupling of energy Siow Plex
faeplona signals, nod eulmeqirnt Tinitatons an Yais exergy anno:
Siva Bete

3 Fiabe: Singing
Finally, we investigate « third imouirment duc to erostal, rolrred
to ne singing. Siging, or spusiows callin, can ooeur around the

‘Panu TItrarmeners Dox To Cuossmax

We ate are
sie are
i ae Tag ag Fi Sr

‘Ga Raat singin eet area so ees iced
‘Spline thew a

INBRT and FERCE anal for read and forend meet eps
enooersua i¢renreRace 429

pth formed by two oppositely-dieeted Pictarephone equaliess and
he twa nens-end crosetle paths comping the ott of one equalizer
{othe input ofthe others shew in Fig

a Mezsurs to Contra the Bie of Crottatl

‘The eects of near-ond erosstale can be mitigated by seducing
‘onualizer spacing ane ths the resized epalver gain, The sialetor
intorfveneo zetia 'e then inoreset I Uhe arouse the equaliser ein
is reduces. 1 the erenire! spel bene: Lon alo bo eeoronse,
‘vidoe none-iad erastak Toes etn bo roalized by sexrogating
Unpositediretione of tranemieson ints aeonesteexble unis, Furcher
echetions ir intenferane may be ajovet iy Ting he mizaber oF
leering systems.

Ecunleyel farend erossuallc ie independant of equalizer spacing
This interference onn bo redueed, however, by imting the overall line
longty, ant by placing resteletons on the zamber of interfering sy
ten, and their plasms thin the eae seat

We present methods of entlyzing che eels wf orostale which ean
de used in waiting esgincering vale. ‘The woneolisturber impairment
is any in Section LV by fining the prabubilicy that cho minimums
cui-to-pis erosstal: coupling lve is los than the quirement. Ran
la nose interference i aoe Seetion ¥ by passing eho nter-
feng erecta through severe chasing filters and chen intesreting the
ontpnt to fad che tote effective inleaesing power, The probability
of singing, or af Ivingelose enough to singing a effect ecko rating, is
computes by « Moate Cael technique in Sestion VL

Ax ua ecmple uf the us ofthese methods, thay are applied to rl
‘ie lowable equalizer spacings using the zequirements and] assim
490 nu um, averme mcmsroaL JOURNAL, FRENTE Tt

‘Tanta L1—Laers ox Eyuatsonn Seana

Type and oornot | cauping | ape
"Fpl BRE | aateae iy ne |

B Woe tiiter | SIRT [ae
wre | pee
AE
cotisioae | yee
Cr ee nae

Rete ing Saree

tions stated in Section THT ‘The sceulte are given in Table TT for tae
indiested aouree and enviealc coupling path. Te figures for tmmmke
fre for the tru ‘alii wing developed, nob for tho equalizere £0
be ued initially. The Tinilalionydifer somewhat betwaer the two.
Other design concideratinns retret equalizer spicing: to 6 ft on
the assumed trimeion sulin. Therefore, spacings beyond this vale
‘are ot given inthe table

"Tae eouttolling impoirment for loop ie singing oF near-singing vad
that for trunks is ruador noise intesferoneo from TI Ties. Thus for
‘otk laope and trunk the desire to keap the umber of equalizers to
s minian by wing Log cqualeor spacings i of the neceasity
to Trt ccualier gaia t recuoe Ue rflentsof nou-ca2 eros. The
Alelatso7 the ellomeale epesings are given below.

Loop equaliser may be epscod 54 kf apart on 2-gauge ecbe il
oppor ireeions of saamsmiesan ace ia eepacte cable urta, When
fpporite directions of sranmnisson roast be placed in the atm rable
Unit, 2 eft aopacution in usable wich acceptable probability nf deg
radation in the gain and phase cheracteristics due to neaeloging.
cmoweniax 1TEaFERENCE ‘ar

‘To obtain Git trunk equalizer epxcing on 22-guuge cable, opposite
directions of Pizturephona transmission must be ia seperate eable
trite and thene ay he no TL or Payee i ony cable uni cube
ing Pietureptore aystecs, In edition, epposie dications of TI end
Pletwrephone tennsmission rast be it note seart ants, Tyas
‘pacing of 47 ile muy be ebsained if oppocite dications of Tad
Pleturophone trenemission sre in adjacent units. If opposite dicstions
of Pistorephone transmission must be placed fm the came exble unt,
Inerferenes due to random noise ray be controled by maintening
sp equalizer apzcing no greaiay than 8.8 il. Tn onder to achive this
spacing of withinunit ond oppositely divected tune equalizer, is
Jnmpovtans ta canrol TH and 2 itesfnencr iy keeping Pictwtephone
Tinee an ue gia (TY en 12) Tins nepal i

2 Cable Charaariatin

ulpeinsated eable of wniesype coratretion i assumed to be the
nium over which anslog Pictonpome viganls ave tranemtted. The
00-paie cable of sis typo in made up of eightoen OD-paineable unite,
cas shows in Wig, 2, Adjecent ant iaennte tite are indicat on the
figure. "The Ines charasteritee 02 i- an! 22-paue.pulp-iealated
fable pris, whiea ane aamumed in this etudy to be the felis for
‘oop and trunk transsssen respectively, ave given jn Fg. 3. Uxper
mentally oblsined crown date for 22-zauge palp-insulated cable
five given in Table TIT The sare values of eoupling loss ave used fo
2b-guuge exble, The lo, in &B, of buch neveend acd farend eno
talk coving i aesunill Wo We wordy distributed 40 2.be wh
smotne that doersue with eequeney ar 46 and BO d/octans, rec
402m em avermne rusuicah JOURNAL, PeaanT er)

tively! ‘The standaad deviation of the dirbution ie assumed to be
Independent of frequency

8 Repuiromenss

‘Tie raquicemanca given by Ul E, Browa? zeeult from subjesth
Atetesvined Tita alested acon the vavioun soporte of the eevait
et rake uy the eomplte evxnwaon, ‘The equal-level croelalk
loss which tows the inteteresee from che wot-dieursing sgpal “0
be noticeable but not objectionable is 49 cB wl 160 Ws © This applies
to both loop andl truncs ns well as to all other parls of the endo
et teanamision path. The requirement for render noise on loop is
fiven a2 © datribvton with mean of —61.6 clin nnd standard de-
‘ation of $0 a8, Althungh Brown farther alloctes the lop noise
Tequizeteat asiong the eynloms thes may compoce a loop, the Loop
Taeiiiy2eze ie aeeumned to be « dines connection bebwitn central of
fine and eubeciber vod iv (herefore alloeacad tho entire roqirement
(On trink the isean ond ecandacd deviation per epan® are specifed
ts —tH.6 dBm and 40 ct soepectively. The minimum singing margin
(Gee Appendix B) reruned to insure that gn equalised Tine has an a
fentably ell probability of singing ie given as 10 dR with proba
ity of 0s,

a Epwiaient Wunder of Ditters
‘Tae delrimental ateeea of aearend ecoslalk rou pmanily at
nqatizer locations, ‘Therefore the equivaimt number of dixiurbere

tna in Fe? of RB
cno86thL IOTERFERENE 483

(ng) thst maust be considered is equal co the number of interfering
signal at each euatir location, a, nluplied by the number of
uate seations, ¢.

Equel-evel far-ané eros coupling is eomputed forthe overall
‘na length eins ite eects are independant of equalizar secing. The
umber of equivalent ditirbes ethevefoneenuel ton, the number of
elu dire

Tn the companions that fellow, it assed that a dated pair
Jn given S0-pui exble unit any be vubjecta to aL ost» = 25 op+
postely-dircted, within-unit dsturbors st aay one equlier loot
Iti furhar semmed thot [ocpe end tric apne wll bo eompaeed of
at moet q = 4 and 6 equalizer sottione, rrpectively. If wl pai within
eable init ate transmiting in the sume diestion, interference ea
‘ny inturbed pir devo the sete of laren erostell, ie ealeulated
‘ocuming w — 80 wilhinanit disuphess. When disturbing and ise
turbed pairs are in adjacen cable wil the Interference i thal rome
ited from n = 60 distsbors, All computations asmume hae the
qusTzars of the disturbing end disturbod eiuite are located ub the
stane point

sua Trae Actity

‘A tafe uotivity factor, deve asthe peroanage of pire tive of
those equipped for Pisturephone (rasanission, ie asumed for Toope
fd trunks, The fueor for loop chnaen tae 0.1 wherens at eed
for trunks ie conservatively taken ms 1.0

‘The anulysie uf woraedisturherinleferenee ia given in Append
A, Tee chown that the equalizer spacing i depertenk spon the aub-

aoun TH—Crosenucx Covruna Loss ar 1 MHa For 22-Gancr
Pour Ivevuaren Came

a Stn aoa |
S|
Hse | & |
40 mp am, aveeme emer. JoUuEA, MMNTARY nt

jective effect of thie interferes, tbe number of equivalent dstachers,
fend the true activi.

"The equat-leval less equine to make this type of intenferane doi-
italy aotossble but not objertionaéle, denoted hy Tong , bas been
tubjecivaly determined to be 45 all at 150 kts Gaetion 8.2). As by
hom ia Hig, 4, a ciatwbing sigaal coupled through the neocond
‘reste ath is oubleet o une gain of the equelier of the disturbed
‘dros, Denoting thie gain in all hy @, the requzed aable eros
‘eoupling los, C, is etl to (Lana ~ @) JB wt 150 XT

"Kaowine the cumulative probability dierbution af the pai-to-pair
crosstlle lies, Fy(2) tho folowing rezult (darived in Appendix. A)
fn bo obtained,

“Assuine {hatin a eabie made up of q equaliser acetions, thee ate
poceibleinleofeote and » possible dscubod cireuits, eh of which ix
fetive with probability pe Then the probability that the onizsom
Dalnorpair Jom between he m interforars end a disturbed circuit
‘dose at random is loss fan th require C, a given by

Fc) = 1-0-0 ag? a

where
a= un PCa a
ad Fis the dnteibutioa of the minimum pairto-pir loss.

‘ht tlaton ie weed 4o obuin tho onreer of Fig. 6, where the prob-
blity of exoveding the revirement on loopa is given usa funtion of
quan spacing, Te equivalent numberof disturbors Is treated a8 8
(perumeter. fs eritorion shins that Limits the probubilyof execeding
The warst-disturbor requirwment to 5 poreers, aad the number of
‘wthiasnis aquiveent daturters ie weumod tn be 25 x 4 = 100, the
‘oarinmuma equalaesspecing is found to be 4.6 ki

"Woeaedisturher Inferernps ia not a problem en trunks evn for
‘ee marimum trunk equabizr apscing of 6 Fl. This follorasizeo tho
fin of the trank ogi for 2-eaugm eae is ess than that supplied
‘the atm Toneth -gsug loop, and therfore « smaller coupling
Joss, Cy i seared.

=> I {>
ik ch

Fig Cron oa, Ce read to met the worst tobe rosie Lam
cemseohae yurrmrrABR 25

5 ae
i

iy, §-Polibiley of emeodig the wort nurer secant om loos tue

‘ven wlien the effete of crosstalk. wr uh evden: ag a distin pat=
tain oroncel yg sons dsturber, ae diaeussed a Sestion IV, wide
‘bend eysteae opereting within the cable coatibute unwanted ensray
rough erostale eaupling paths to a Picturophone creat. This ea
tay muse be aken ibs acount, snd i eested here random mage

"Tho efeste of andor noize on equaiter epscing and peir place-
rent ser cherihed jn che felling setiong. "The model used to do-
trmine sho recived noisy power cue to netrend and Far-end crear
tall coupling of Picrsphone, TI line, sad 72 line signale are chow,
in Fige, a und 6b reswetivrly, ‘The eqaliser guint inode in
Fig. ih beesves in the fare orocaatk ese, le dislarbing vgn be
spose to rable lee equ to fh gun supple by Uhe equalier of the
Gisturbed ine, Ae shown, Che incerfering touree i eospled through a
frosstallc path, assed to be thst deeribed in Seotion IIL The Pic-
burephons sulinas gain (ineuded the neas-end ocee oly) He ae
fumed fo muatsh the late, ot nominal tumporaure, of @ given lenge
of 6- or 22-gange pulp cable. Daemphusis is used to prove inezeazed

smnity to high frequency interference? and noise sighting ia im
‘laded to aeooumt for subjective woighting of noise by the human eye
‘The chusierstie of ecavion set vollof, used to echenee piokire
suet, wcvanntee the eroeived sigeal e¢ the high end of the band
496° vem mm svevam tunica FOURDEAL, PHOMTART 71

snd, threfore, ut be inolule The cheractaristies of noise weigh
ing plunroll-c€, end ceeraphass are shown ia Fi, 7.

"From ig, Ga the mean aoiee power at any #roqueney dow la inter-
ference eoapled through the acernd pile given by

ID = SGN DIOR c
vhece SU} in the icerfering voner spectrum, Xf) the mess cross
tale Hse function, G7) the erties gain, nd Dip), W () snd 2)
Uke doomphasi, noite weighting, and station set rll characteristics
reepactively. The exorestion for noise coupled through the fem-end
trotaalle il is Une ene, except for the gain factor, '(), whieh is
tot inckuged, Nomereal tegration of equation (8) yields Ube mear
noise power onthe dvlosbed pair due to one distrber. The amplitude
‘Gatrtation of {)) ie based on the lognormal distsibution of eros
{SLE loa, and is dhorefore alan normel in is. The probability distribu
tion of the noise powe- cesumuleted irom ng equtvalent diturbers is
found By convolving the lognormal dictebstion ng times The noise
power exeeeded with some given probably ean then be determined.

"Tho noe produged throu Sard erosstall eoupling is eslulsted
by ict finding the farond orosiak loa dizibution for the total
‘oop or trunk span Length of inlotest cnd then applying the model of
Fig. 6b, The wolke due tam aolaal dslrbers is cetormized by com
Solving the ezplilde dietrbution of the noise ganerated by « single
“itunbern times,

62 Intrernae Brom Pictursphono Simals
‘Remate are naturally depeaent upon the acureo of th interference,
the Picurephons signal Inthe wiudy the preamahesied Picturophone

wo

Pig. eodet wed snp andes ace ntrarane cupl thea
ed meet Sal RN Be ca ae ae