video technologies for mars - mathematical software · nmany video formats, bit rates, etc. nwhile...

John F. McGowan, Ph.D.E-Mail: [email protected] 9/13/99 1

Video Technologies for Marsby John F. McGowan, Ph.D.Desktop Video Expert CenterNASA Ames Research Center

Mail Stop 233-18Moffett Field, CA 94035-1000

Web Site: http://zeus.arc.nasa.gov/


Introduction

n One desirable goal for missions to Marsis to provide real-time or near real-timetelevision quality full motion video.

n Studied for a Mars Airplane mission tofly small plane down the Valles Marineriscanyon on Mars for thirty (30) minutes.

n Micromission for Year 2003 included inthe NASA Year 2000 Budget Proposal.


Introduction

n The issues are largely the same forother Mars Airplanes (aerobots).

n The issues are largely the same for MarsRovers (telerobots).

n The issues are largely the same fortelevision coverage of manned missions.


Valles Marineris


Valles Marineris

n May have been formed by flowing waterin the distant past.

n Other possibilities? Tectonic or volcanicactivity? Fissure from asteroid impact?

n High resolution zoom pictures of canyonwalls to look for sedimentation or otherfeatures.


Wings on Mars

n There have been many proposals forairplanes to fly on Mars.

n Larry Lemke et al recentlyn Many more. Apologies to the unnamed.


A Mars Airplane


Kittyhawk (MAGE Proposal)


Ames Plane for Year 2000


Baseline Proposal

n NTSC Color Television Camera (CCD)n MPEG-1 or MPEG-2 Encoder Boardn 352 by 240 pixels at 30 frames per

secondn 4:2:0 Digital Video Format (subsample

the color components by two horizontallyand vertically)


Video System Parameters

n TOTAL WEIGHT: 2 Kilogramsn TOTAL SIZE: 120 mm by 220 mm by 30

mm (792 cm3)n TOTAL POWER DISSIPATION: 20 Wn BITRATE: 1.2 Mbit/second (not including

error correcting codes)n MINIMUM ACCEPTABLE BIT ERROR

RATE: 10-6 (assuming random errors)



n 1.2 Mbit/second exceeds any bit rateachieved from Mars to Earth.

n Constant Bitrate (CBR) MPEG Encoderif possible. Given very tight bitratecontraints of communication links, wantto limit the bitrate to fixed maximum ifpossible.


Back of the Envelope

n TOTAL WEIGHT: 1 Kilogramn TOTAL SIZE: 100 mm by 200 mm by 10

mm (200 cm3)n TOTAL POWER DISSIPATION: 15-20

Wattsn Based on COTS CMOS components!n NOT SPACE QUALIFIED


Hitachi MPEG Camera

n TOTAL WEIGHT: 540 gramsn TOTAL SIZE: 83.8 mm by 142.2 mm by

55.9 mm (666 cm3)n TOTAL POWER DISSIPATION: 6.5

Wattsn Includes battery pack, hard disk, etc.n NOT SPACE QUALIFIED



n This conservative estimate includessubstantial extra weight and volume forradiation shielding, rugged packaging,and extra power for heaters or radiationhardened CMOS.

n The overhead for error correcting codesis not included since this varies fromcode to code.


Reasons for MPEG

n Many verified (tested and debugged)real-time MPEG encoder and decoderchips and chip designs from multiplemanufacturers exist. Selecting MPEGdoes not lock NASA into a singlemanufacturer or design.


Reasons for Using MPEG

n MPEG is an International Standard fromthe International Organization forStandardization (ISO) and is the de factoworldwide standard for broadcast andconsumer digital video.

n MPEG video is used in most digitalbroadcast and consumer video systemsand products.


Reasons for MPEG

n GA-HDTV (USA) uses MPEG-2n DVB (World) uses MPEG-2n DVD (Digital Versatile Disk) uses

MPEG-2n Cable TV (USA and World) use MPEG-2

to distribute video.n DirectTV (Hughes) is essentially MPEG


Reasons to Use MPEG

n MPEG is scalable.n Many video formats, bit rates, etc.n While propose here using 352 by 240

pixels at 30 frames per second in 4:2:0digital video format, known as SIF(Source Input Format), many other videoformats supported, for example 720 by480. Not locked into 352 by 240.


Reasons for MPEG

n Successful products use MPEG at 352by 240 pixels at 30 frames per second in4:2:0 format (SIF) using the defaultquantization matrices, meaning 1Mbit/second video, to provide televisionquality video.

n VideoCD players, CD-I players, etc.


Reasons for MPEG

n MPEG compression outperforms mostother image and video compressiontechnologies.

n Wavelet video and image compressionis not standardized. All workingimplementations are proprietary. Veryfew hardware implementations exist.Expertise is hard to find.


Reasons for MPEG

n MPEG is preferable to the ITU-T H.261,H.263, and H.263+ videoconferencingstandards because MPEG supports bi-directionial predictive pictures, Bpictures, for better compression.

n Videoconferencing standards aredesigned for “talking heads” video withstatic backgrounds.


Reasons for MPEG

n MPEG is preferable to ISO JPEG stillimage compression, e.g. Motion JPEG,for full motion video because MPEGexploits the small differences betweensuccessive frames.

n MPEG has much greater compressionratio than Motion JPEG.


Reasons for MPEG

n C programming languageimplementations of MPEG encoders anddecoders, both MPEG-1 and MPEG-2,are publicly available.

n ISO Standard Documentsn Over a dozen in-depth books.n Many MPEG Experts


MPEG Problems

n MPEG is sensitive to single bit errors. Ina worst case, a single bit error cancorrupt a half-second of video.

n No publicly available Verilog, VHDL, orother Hardware Description Language(HDL) MPEG encoders or decodersexist with timing problems solved. Allhardware implementations areproprietary.


Hardware Video Encoder

n The Mars Airplane will need to compressthe “low resolution” video in real-time.

n 30 minutes of uncompressed NTSCvideo is 131 Gigabits (color) or 44Gigabits (black and white).

n MPEG at 352 by 240 by 30 frames persecond requires 5,000 MIPS to encode.


Alternative Compression

n Wavelet Video Compressionn MPEG-like video using Block Discrete

Cosine Transform (DCT) and motionestimation, but designed to reducesenstivity to errors. For example, ErrorResilient Entropy Coding (EREC)proposed by Swann and Kingsbury.


Color and Bitrates

n Can reduce bitrate slightly by sendingblack and white, the luminance colorcomponent, only.

n Color is already subsampled in 4:2:0n Naively one third of 4:2:0 video is colorn MPEG compressed color more.n Only gain about 20 percent.


Below Television Quality

n 15 frames per second (jerky)n 176 by 120 pixels (grainy, blocky)n Increase quantization step size (artifacts

such as blocking, ringing, and blurring)n Push down to 384 Kbits/second?

Quality will be poor.n Slide show may be preferable!


Noisy Channel Issues

n BER 10-5 for current missionsn BER 10-6 by 2003?n Error correcting codes add to required

bitrate but are needed to achieve “low”bit error rates in deep space.

n MPEG sensitive to bit errors.


Noisy Channel Issues

n MPEG at BER of 10-4 is visual noise!n MPEG at BER of 10-5 is poorn MPEG at BER of 10-6 is fair (can use)n MPEG at BER of 10-7 is good (can use)n Actual errors with error correcting codes

are not random bit errors :-(


Space Hardening

n 10-20,000 rads (Silicon) for Earth toMars missions.

n COTS parts have thresholds as low as500 rads and as high as 100,000rads(Si).

n Off the shelf MPEG Encoders arecommercial “bulk” CMOS. May notwithstand radiation. Must test.


Space Hardening

n Aluminum box around MPEG EncoderBoard.

n Rugged circuit board and packagingmay be required.

n Radiation hardened CMOS or SOS maybe required (Single Event Latchup).Radiation hardened MPEG encoder chipor chip set is big project.


Space Hardening

n MPEG chip design is demanding!n High risk of failure.n No public timing information.n Timing changes for each semiconductor

process.n MPEG sensitive to small errors. Must

get the design right.


Space Hardening

n Commercial Single Chip Real TimeMPEG Encoders

n Video Clock 27 MHzn Internal System Clock 54 MHzn 3.1 million transistorsn 0.35 micron commercial bulk CMOSn 1.5 Watts at 3.3 Volts


Space Hardening

n Hardware Single Board H.261 VideoEncoders based on Chip Sets (14ASICS) have been designed and built.

n Run at 13.5 or 14.318 MHz clock speed.n Using 1 and 1.5 micron commercial bulk

CMOS in early 1990’sn PROBABLY CAN BUILD RAD HARD

VIDEO ENCODER BOARD!


Slide Show Option

n 8.25 Kbits/second Mars Pathfindern Max 85 Kbits/second Mars Global

Surveyorn 256 Kbit/second in 2003?n Slide Show (reduce frame rate)


Slide Show Option

n MPEG exploits small differencesbetween successive frames.

n At low frame rates (1 frame per second)differences between successive framesmay be too large for effective use ofMPEG.

n Errors propagate across frames inMPEG.


Slide Show Option

n At some low frame rate, better to use stillimage compression such as ISO JPEGstill image compression for slide show.

n Still image restricts errors to a singleframe.

n Naive MPEG at 1 fps: 33.3 Kbits/secondn Naive JPEG at 1 fps: 66 Kbits/secondn Still a demanding bitrate for Earth to

Mars


Slide Show Option

n POWER, WEIGHT, and VOLUMEessentially the same as MPEG videosystem. Just substitute still imageencoder, either ASIC or CPU, for MPEGEncoder.

n Space Hardening Issues are the same.n Noisy Channel Issues may differ.n Can use software image encoding.

More flexibility. Wavelets!


Mars Local Relay

n Several Gigabits of RAM has been sentto Mars already.

n 30 minutes of MPEG-1 video requires1.8 Gigabits of storage.

n Can forward stored video at slower thanreal-time rates, e.g. 256 Kbits/second

n Several hour delay with store andforward.


Mars Local Relay

n Several Gigabits of RAMn High Gain Antenna to Earthn For Valles Marineris, a communication

satellite in Geosynchronous Mars Orbitover the canyon seems ideal.

n Fly Mars Airplane toward a land stationon canyon floor?


Mars Local Relay

n Geosynchronous Mars Orbit Satelliten Delayed Flyby of Mars (as in MAGE)n Balloonn Land Stationn Other concepts?


Mars Local Relay

n A store and forward relay on Mars or inMars orbit can retransmit corrupted data.

n Retransmission eliminates noisy channelproblems at cost of longer delay. Mustwait for retransmission of the corrupteddata.

n With four to eight minute Earth to Marsdelay, video is never used in real-time.


Mars Local Relay

n A Mars Local Relay, especially aGeosynchronous Mars Orbit satellite,can be justified to support multiplemissions, not just Mars Airplanes.

n Local Relay can include scienceinstruments.

n Local relay could include video cameraas well. Dust storms.


Mars Local Relay

n Can relay be a micromission itself?n Accompany the Mars Airplane somehow

arriving in orbit ahead of the plane?n It is difficult to secure funding and

support for pure support missions thatenable other missions since there is noimmediate payback and dollar cost issubstantial.


Conclusion

n TOTAL WEIGHT: 2 Kilogramsn TOTAL SIZE: 120 mm by 220 mm by 30

mm (792 cm3)n TOTAL POWER DISSIPATION: 20 Wn BITRATE: 1.2 Mbit/second (not including

error correcting codes)n MINIMUM ACCEPTABLE BIT ERROR

RATE: 10-6 (assuming random errors)


Conclusion

n Principal obstacle to video appears to bethe limited bit rates of current or nearfuture Mars to Earth communicationlinks.

n A local relay station such as aGeosynchronous Mars Orbitcommunications satellite may offer asolution.


Further Information

n White Paper on Video Technologies forMars Airplane

n http://zeus.arc.nasa.gov/mars.pdfn In Adobe Acrobat Portable Document

Format (PDF)