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https://ntrs.nasa.gov/search.jsp?R=19790002102 2020-05-22T14:36:45+00:00Z

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c'OINA11 1 NI('A'I'l0N til'ti'1'h;11 ANAI,I'SIS

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NASA ('ontract: NAS ,)- 1 4 ,1. 1 0

(NASA -Ch - 1 c; 1844) COMInNICATION SYSTEM 879 - 10273

ANALYSIS ro p MANNrD srACE FLIGHT TechnicalDeport, 1 .tun. 1477 - 1 Aug. 1 1178 (Cityroll. of thr City tiniv. of New York.) 21 1` nncIas

tic A02/Mr A01 CSCL 1 7 P G3/32 36P7A

Donald I,, Schilling

Prot*r y sor of I-:lrctrical F:nginrrring

Principal InveAl igator

('0i11W I NIc'ATIONti til'ti'1'i:\ ;ti LABORAWR1'

P1-:F'ART',J'N'T (-)l F1.F: -rRICA1. 1-:NGlN1-:VIIING

Ir ,

THE CITY COLLEGE;,.. THE CT FY UNIVERSITY of NEW YORK

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CODIAIUNICATIONS SYSTEM ANALYSIS

hOU MANNED SPACE' FLUNIT

June 1, 1977 - August 1, 1978

Johnson Slmce Center

Ilollstoll, Texas

antler

NASA Contract: NAS !)- I :iJ•10

Donald L. Sc•hillin^

Professor of E'lec • tl • ival L•'nt;illecring

Principal Investigator

COMM UNICATIONSSYSTEMS LABORATORY

DEPARTMENT OF ELECTRICAL I•:NGIN'EERIM;

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1j Yl d 3 r I ^ ! r PI1 3 1 ^\w^ 7 '1

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It

Introduatloll

This roport aummitozes (Ito clovolopment of adliptivo dolbt nlocinlators

oapablo of digitizing it video signol. The deltic modulator anoodor aeeopts it 'I Alliv,

blaolc and white aouiix)Sito video signal or it color vldoo signal ancf oticodos it intoit stream of binary digits at a ruto which can bo nclJustact from 11 Alb/a to 24 Mb/s.Tito output bit rato 1s clotorminod by tho us0r and otters Iho qualtty of (Ito videoploturo. Tito digital sign it is cloaoded using tho adaptive dolllt modullitor docutlerto oconstriiot tho picturo.

roliotvtag It 10119 1118101.31 of 000Watioa-botwoat NASA and De. Sohilliug.

an A,MI systam Netts dolivereci to .1SC. Tho hyotom 1s onpablo of vneoding blaolci and whito or color video or ouooding froi :o Buquoai:1111 color. '1`110 eolor s1goals

woro 0000dod tit wd Alb/s, tho franca sequentbat color at 16 Alb/s mad tho blaolc-nail-

whita vidoo tit frequone.ies from 8 Alb/s - 1E Alb/S.

This Contract supportod tho follotvtag griuhutto stutloats: 11. 1.0 :uul

N. Soltailtborg.

2)

VIDEO ENCODING USING ADAPTIVE DELTA MODUI ATION

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A13STIIACT

This papor describes several adaptive delta modulators dosigned

to meet NASA's potential neod to digitally encodo video signals.

The adaptive dolta modulators described are:

(1) One-dImensionnl ADM to encode black-and-whito pictures

and also transmit digitally encodod voice with no increase in

bandwidth

(2) An ADM to encodo fiold-seduontial color:

(3) An ADM to oncodo color video signals.

The whits described operate at bit ratos that can be adjusted from

6 Mbps to 24 Albps. The effects of the bit rato and chnhmol errors on the

response of the picture are discussa,d.

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I. INTRODUCTION

it is often desirable to digitally encode a video signal. Such a signal

can be transmitted with significantly loss power (lower SNI1) than an analog

signal to obtain comparable quality of reconstructed signal. The digital signal

can be easily encrypted to insure privacy and can, more readily, be stored in

memory for applications requiring slow-scan video transmission.

There are many techniques available to digitally encode a video signal.

They include PCM, Differential PCM, Tran p fornn Coding followed by PCM, and

Adaptive Delta Modulation (ADM). This paper describes the rosearch performed

by the Communications System Laboratory at the City Collage of New York for

NASA-JSC.in the development of low cost, low bit-rate ADM's capable of oncoding

black-and-white and color video signals in the presence of high bit error rates.

Our initial results and a summary of other techniques have been described in a

previous paper. (1)

Figure 1 shows a simplified picture of the video frame in which there

are 500 lincs/frame. If the video signal is bandlimited to 3.75 MI1z, the Nyquist

sampling rate is 7.5 M samples/s. Since the frame rate is 30 frames/s, the line

rate is 15, 000 linos/soc and, 500 samples are taken each line. There arc there-

fore 250, 000 samples in a frame. Each sample, as shown Ili Fig. 1, is called a

pixel or poi.

Wlien using PCM, 6-8 bits are transmitted for each Nyquist sample, with

DPCM 3-5 bits are transmitted in the same time interval and using ADM we

`I

transmit 1-3 one bit samples during this time period. Thus ADM can operate

at a lower bit rate than the other techniques.

ADM encoded video is relatively insensitive to channel errors. PCM

noticeably deteriorates at bit error rates greater than 16-5, while at 1074, tine

effect of channel errors is barely noticeable when using ADM and complete

recognizability and intelligibility remains even at error rates as high as 1072.

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l+'urtherntove, AUM Is 11 relntivoty low-Cost aystunt. Tho sysle.nt

showtt In 1`il;. 2, conat.ructed by DI,.UTAMODI11,ATMN, INC., employs only

10 IC ahq,s whleh fit on It 8111It10 7" s 8" prlaled c{rcult Ixlard.

R. TIIN AMM 10011 \'IDEl) ENCODING

A block dhtgram of nn AIM for video oneodin{; 18 shown p t Vlg. 1.

"I'ho Input video all,nal (111(t)) Is sautlaled at or Itbuvo the Nyqulat vain to Corm

nt(Irh1). This 8nmgled valuo Ia uont{uared will,dhu estlntlde nt(1:13) a+here

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o(Irt •1) ^^ age (n,(Ic11) 111(1:+1) )

(1)

The oatinuatu Al (I:'a1) Is I'orntell Iron, tho old ost,huato n, (,,) and till)

Step S(k+l) Which Incrtoncnts the est{mnte.

tit (Ir11) _ LT tn(1:) •1 . S(1r11)

Equation (d) shows that; ill (1;-1 1) Is fo,a,d by p:tsa{n11' S (104) 1,ht`01101 It loaey

aeeunuitator, 1.u., it navrowbalttl digit-11 low piss filter. The aealtar a w 0. 08

Insures satisat¢tory error corroelloa L, Lilo decodor. (1) tit tlw ettcedor ti, aaa

be set to oni(y without dol,radiai; tho sysieu, porror,lmneo.

Tho algor3thnt employed to {tc livra.to the stop 8(101) Is

S(k) I r e(k) + 0, i1 e (I:-1) 1

II\ 1b tip o (I)

Stj S ( Iz) t 1 ti S0

I s (h) I S0

S (I:) I : 15 $0

(',Ill)

(3b)

(3c)

8 is the mildmunt step-size trod Is equfvalo11t, to ona quantl„atlun love;. The

timnimuna step is - 11'.8 Sd , or d ;ails, as is the sliumt tu(1:11). tilturalior. lottle

Is employed in the, uiroutt osed to genorato Iiq. ” to prove it ath l orsu efl'ccta

whoa tile milleroterlows duo to chtutnel errova.

5)

Emeoding of it moving scone using tile ADM results L1 no

distortion or other dolotorlous effects. Figure 4 shows Tile oportition of

this ADM lit bit stunplinh rates of G, 11, 10 and 221f1bps. At 0 Millis Lilo

"adgo-busyness" is Scott be oatronioly pronouaoed and the writing

1:ItLj+ Su got tlluo oil card lit legible. At tl Millis (approximately

1 bit/poi) the edge busyness is reduced significantly but tic writing is not

quito legible. At 16 (approximately 2 bits/pel) and 22 Dlbps the "adgo-busy-

ness" Is ne longer noticeable and the writing is legible. Note that ilia improve-

mont obtained whoa Incrousing from 15 to 22 Millis is not significant.

Figure 5 shows the rosponso of the ADM to chunlul errors when

the video signal is munpledi :at 20 Millis. I?lguro 511-e shots lho response

of the ADM when the Po = 0 to Po = 10-2 rospectivuly. An occasional error

Is obsorvablo at 10 whllo the presonco of errors is quite noticeablo tit

P = 10 2. The rospoesc of (lie ADAI to a uniform grey background lit high0 2

noise enviromnnlit (P = 10 ) is shown lit 5f.e

Note that the errors do not cause the picture to "bre:dc -up", i.e.,

they do not significantly ai'foet the lorizontal or vertical synch pulses even

at an error raLo of 10-2 . Tile instead, act lIko till "overlay" of

horizontal streaks and ono has the fueling that if the overlay could be ramoVed

a "cio:ill" picture would result.

111. ,,NCODING COLOR SIGNALS

A. Field Sequcutial Lacotl[111: of Color Sign;Lls

A field sequential color system Is illustrated in Fig. G. In this

system the ADM encodes soquontially, the red, green and blue signals available

at the camera output. For osaniple, during the first field tho red color is

cncodcd, during the second field the green color is encoded and, during the

third field Lilo blue color 811; • 11111 is encoded. Along with the simplicity of the

color camera, the ad vantage of this type of color system is that the bit: rtdc

0)

17

is the stuno its for blade-and-whito pletures.

The ADht wits constructed and tosted tit JSC In a field sequenthil

system. Vigurc 7 shows the straight-through and AUM oncodcd rosponscs

whon using a flold sequential system.

Tile disadviuttsgo (I :iris system is that only ono color signal is

encoded from ouolt field and the color componoats of do picturc hntd to

soparaCo at the edges of moving objects. The color frame rato is only 10

fraineswecond. l,xcopt for this defect, which is charitotcristic of any field

soduential system, there is no upparont distortion added by tine ADM. Silica

edge busyness is a random function and it characteristic of theso ADM i s, it is

interesting to noto that the busyncse Is masked by the superposition of tic

throe color friuitos.

ii. Direct: ADM bneoding of NTSC Video

The ADM characterized by > qs. 1, 2 and 3 can be used to encode

NTSC color video signals. Pigurc i!a shows the straight response of the system

without Clio ADM. The picturc used was takon from im al'tornoon "soap opera".

Pigura tab shows the siuno picture encoded at 10 Mbps. The pictures wore

talcon at a rate of 130 second which resultod in Cho dingoual stroaks shown.

Note the slight edge busyness luttl Cho grtunularity tint is prosout. Also,

obsorvo the slight loss of doktil in the norkboo.

Figure 0 wits taken from a morning (11112 program. Such progriutts

gonm•ally have oxtaonnoly vibrant colors. Note again the proscatco of the

diagonal stroaks. Theso pletures were Utken at a sampling rate of 24 Millis.

In general tho actual picturc (1utiltty If much botter than, that observed

from those figures. <:1

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C.l:n(^u(tlty Uatu^llamn^(ilials 1`I1lovill

The ADDI 11110 it tendoney to 01opa overloud if tito inconiill y; aiganl

has largo high-frequency compononls. 't'a ovoid Walla ovorlond one elm

ineronso ilia bit veto. Alternately, ono can low pass filter the rlignal prior

to encoding, thereby decreasing the amplitutto of the high-frequency portion

of ilia video apactvum. Such it flltar is called it "decmphasis" filter. lit the

receiver the ADU decodor Is followed by it " proomphasla" filler to reslora (Ito

ilia high frequency Vomponauts of ilia signal.

tl11111to FAI whore the deomphasis filter is it single-polo 120 low pass

ftltor, ilia domuphnsas liltor needed for color eneo(UnK must bit it tntiltlpla polo

filter. Several filters ware, attempted. The filter neluotod Is sliowtt In PIg 10;10

VIg 10b shows ilia system configuriltlon whilo Fig 100 allows the elvoult used for

anch section. Tito vtthtos of 1, aid C determine the Q of the section and ilia series

roaonanae. '.Cho Values of (, and the resontult frequencies wore chosoo to optimize

ilia trn(leoff between ripple mid high fregaancy noise.

Flgere 1111 shows the straight through respunso of an NTSC color

system, Fig. 11b shows the responso of the direct encoded ADM tit 2.1 Albps tuul

Flg. Ile shows the respouso of rho Al)1i whoa (leenlphasis filtering is employed

lit ilia. olleadar at ilia at(llio si lulling rate. Note that ilia. skin cois!ploxlon Is

greatly Improved what using deumphas[a/pr cuniphasis filtering.

1). Digital Voice rind Vldea TndtUli? Ina

It is often convontent to t:runsnlit voiceoi sinitlItnnconsly with the video

signal. This Is validity accomplished without nny Increase Ili bit .rate.

The ADAI described above encodes tiro aollilKwitc riche signal, 'i.e. ,

tine video ,Information and the horizoidal raid vortleal synch pulses. Sinew the,

synch pulso is it large negative puisu ilia AD1l goes late saturnl.tgn and gouevnies

it long stream of O's. Whoi oparnLing tit 20 Albps tipproximaiely 00 O's occur

coilsccutively.

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If voice Is encoded at tilt) rttto of approximately 391;bps, Lilts

of voice clot be transmitted during each horizontal synch ptdso. I gor examplo,

to tlgiui the encoded bit 1 0 we odd it header 1 1 1 to (he bits suit add the five

bill 11 1 1 q to tiie all- uro [)tilt encoding the horlrosial retraee, The result

Is tho trnoamisslon of 39 klips with ' 1 0 hibpa vidcu e,t(lt 110 increase Ill

bit rnto. It should be clear that data as well as voice eml be nutlUplexed In

this way.

The video oacodur/decoder with till nudio channel designed by

1)i;t,TA1)'0IyLtLXrl0UAF, INC. (Model 910) transmits it 3-blt code for caeh

informlition bit of tiro tiigital voice thereby providing y iaipie, yet effaetivo,

single-bit orror-covrect.ton.

1V. Nt \Il AREAS OF HNSNAIWIi

A. Milo Sequential Color MicodIM

Tho difficul4v with field segtuential color encoding is that during periods

of rapid motion, the color hl each field will nut lino up; after ;ill Itlahes 1/60

second to eaeado till field.

Tho above problem can be siltnifivaatly rcdu0ed by encoding a <tifferent:

color for eneh line. rov example, encode lilt, red Color of lin g 1 1 the green color

of lino 3 and (lit) Woo color of HilP S. Vat) Ihesta three colors oil 3 of the

monitor. Next encode Wo red color or Itae i and display file throck colors of

lines 3 1 u and 7 oil G of tic motdtor, tilt,`. 'fits system is now boirg eou-

4tructed and will be tested tit 4SO.

11. Shiw-Scan \'idro A;nrotltnt;

1 1 CM encoded slop-scan systems rrqutre it friune of digital memoey it,

the triinsmitter and ht lho receiver. When ADM eneodhig• [it only (he

0(10 bit starettin lived ho encoded. Thus, file tunount Or Incmory ,required Is

;rued by a Parlor of ;iplaroxfni;tlely + d.

A ADM system has been designed and is currently being,

=77 7777177 71" 71 "R 7`1 1 11A .1 1 -7U)

ponstructed for testliy, at J80.

V, CONCLUSIONS

Once one remlizos that it digital ny4tom costs no more caul often

less thtul an analot; system, is more reliable anal provides hlgher quality

performance at signtf etintly tower SIS1 11 0 the conclusion Is usually roaehod

to "go-diglial".

'I'wo drawback it) it dtglial system tlo exist. 'I'ho 111giial aystpm

often requires w1der bandwidth and, 1:01.4 devices often 111111 1. the speed it

which cllgliai eircult can operato to values which are less than desired.

When Lnvesugatillg which zilglial sy,stom to employ we awst Conskler

cont as well its quality, if coim>wrclal ov near commercial quality is required,

If rerogaizabiltty and lntolligibillty are Important, If small nine, low power and

low cost tiro factors wortity of consideration and sul'fielent btuahvidth is nvail-

ablo, then one should, as ,INA," is doing, took at ADM.

Tn this paper we have extended the results of our original paper (1)

and looked 11140 at color video and audio on video. ',Cho results obtained

from till lesis porformed by NA.1 indicate 11 pleasant quality picture, wlllelt

Is not degraded by mo(ion.

VT. 111 11 1-L'lil NCHS

(1) "AT)A1 Systems for Video l.nooding", 'f. It. Let, N. Scitoinberg

and 1). L..kthilling; 11 1.K Trans. oil Comm. Vol. Coal 39, No. Il,

November 1977.

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SOhetuburg, No 1). L. 50111111111P and J. Uarociniek, "Video I;nOoding WNlnt;

Adaptive 1klia Modolatton ' , 11; 1; 1r; Trnnu110tlons on Co incacm fe ll Uons,

Sy)0atnl Issno on Shuttle ConnnmrtGnUons, November 10711.

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throu-411 res po lise. (h) Encoded usin t"' . A1W.

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Fig. 8 Pictures obtained using; NTSC Video. (a) Straight throuhltresponse ctf color syst('11, 4b) AD11 encoded picture at 15 AlI)its/s.

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response. (h) Encoding a g ing ADNI. (c) Fneoding using deemphasis

filtering; and A0\1.

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