Digital Television (DTV) Technology And NASA Space/Ground Operations

Transcription

1 Digital Television (DTV) Technology And NASA Space/Ground Operations Mohammad Amanullah (LMSO) Lockheed Martin Space Operations Consolidated Space Operations Contract (CSOC) Abstract This paper describes the current and future applications of Digital Television (DTV), both High Definition Television (HDTV) and Standard Definition Television (SDTV) in NASA s Shuttle and Station space/ground operations. Following an overview of DTV technology, the current status of DTV in NASA operations is described. The paper reviews advantages that DTV offers over analog video, and the various projects and plans for the transition to digital television technology. The paper describes NASA s current plans for moving from analog video towards DTV technology for downlink, uplink, distribution and display. Downlink Shuttle video in digital form was transmitted and distributed during STS-110 in April The technical cooperation between NASA and other International Partners is also covered. For example, NASA and the Japanese Space Agency, NASDA, are working toward a live HDTV downlink demonstration next January/February (2003), during the STS-114 flight, which will include a Japanese crewmember. In addition, the paper will cover the working groups addressing related issues, such as DTV standards and the approach to archiving DTV data. The paper concludes with a summary of the status, plans and recommendations for applying DTV technology to ground based space operations at NASA. Finally, recommendations are made, based on industry research, for HDTV standards at NASA INTRODUCTION The analog television standards for NTSC, PAL, and SECAM are 40 or more years old. They have been extremely successful and are still serving well, but they are based on the technology of 1950s. NTSC systems are used in North America, Japan and the Philippines. PAL systems are used in England, Germany and China. SECAM systems are used in France and Russia. For at least the last 15 years, research labs around the world have given much attention to the design of improved video systems. Because the most obvious improvement is increased resolution, this work has been named High Definition Television (HDTV). Early HDTV system proposals were based on analog technology and generally required some means to provide more bandwidth for each channel. This posed serious problems regarding spectrum allocation for broadcasting and the reduction of channel capacity for cable distribution. Recent developments using digital technology have shown that HDTV signals can be broadcast or distributed in the same 6 MHz bandwidth used for the current analog television. In addition, the flexibility offered by digital systems enables many new features that greatly increase the potential usage of HDTV. 1

2 Present TV Standards Around the World SYSTEM ASPECT INTERLACE FRAMES/ TOTAL/ACTIVE LINES/ BANDWIDTH RATIO SECOND LINES SECOND (MHz) UNITED STATES Color NTSC 4:3 2: /480 15, Color HDTV 16:9 No /720 45,000 6 Color HDTV 16:9 2: / ,750 6 ENGLAND Color Pal 4:3 2: /580 15, JAPAN Color NTSC 4:3 2: /480 15, FRANCE Color SECAM 4:3 2: /580 15,625 6 GERMANY Color PAL 4:3 2: /580 15,625 5 RUSSIA Color SECAM 4:3 2: /580 15,625 6 CHINA Color PAL 4:3 2: /580 15,625 6 Why HDTV - Leading up the Grand Alliance Research in HDTV had been going on in the United States over a decade. In 1987 a group of television broadcasters petitioned the FCC to consider setting broadcast standards for an advanced television broadcast (ATV) service. The FCC response was to set up the Advisory Committee of Advanced Television Service (ACATS) to consider system proposals. Several test centers were established in the USA and Canada to test the HDTV system proposals. Twenty-three different proposals were submitted to FCC. The FCC announced the following basic ground rules: HDTV should be a separate service broadcast simultaneously with NTSC service, rather than an add-on to the NTSC broadcasting channel. Both NTSC and HDTV services will be available until transition to HDTV is complete, implying that HDTV must fit into a single 6 MHz channel. 2

3 Some of the system proposals were for extended-definition TV (EDTV), which offered increased definition while maintaining some compatibility. The FCC preferred to first consider HDTV proposals that have increased definition not constrained by any need for NTSC compatibility. As a result of these guidelines, the system proposers went back to their drawing boards. General Instrument Corporation made the first all digital HDTV system design. By 1991 four all-digital system proposals had been submitted to the FCC. The Advanced Television Test Center (ATTC) and Advanced Television Evaluation Laboratory (ATEL) tested these four and two analog/digital proposals. In 1993, the ACATS tried to pick a winner. However, the only thing the ACATS could agree on was that the system should be all digital. The ACATS subsequently endorsed an industry effort already under way to merge the four digital proposals into one - called the Grand Alliance (GA). This was formally announced on May 24, 1993, and it comprised the following seven members: AT&T General Instrument Corporation The Massachusetts Institute of Technology (MIT) Philips Electronics North America The David Sarnoff Research Center Thomson Consumer Electronics, Inc. Zenith Electronics Corporation. Over the succeeding months, the Grand Alliance system details were crystallized and, in 1994, the system construction and testing of HDTV began. Since 1994, digital systems have matured and HDTV/SDTV systems are in the process of being incorporated in the broadcast/cable industries and other private/government sectors. Advantages of DTV Technology Over Analog Technology The use of a digital rather than an analog format for broadcast signals, as proposed by the Grand Alliance, has a number of major advantages that can be summarized as follows: Bandwidth Conservation - Perhaps the most obvious advantage of digital formats is their major conservation of bandwidth by the use of data compression algorithms. For example, the display formats proposed by the Grand Alliance for HDTV would require a video bandwidth of nearly 24 MHz (per component) for conventional transmission. With digital transmission the modulated carrier, including video and high fidelity stereo sound signals, can be accommodated in a 6 MHz channel. Interference Immunity - Digital signals cause less interference to other signals and are, in turn, less susceptible to interference from other signals. In addition, HDTV channels can be fitted into the spectrum gaps in the NTSC assignments table. Signal-to-Noise Performance - Digital transmission systems have the characteristic that they add no noise to the signal, provided the bit-error-rate (BER), remains low enough to be within the range of error-correction circuits. Under this condition, the digitally transmitted signals are either excellent or they are totally lost. Signal Distortion - Analog transmission inevitably causes at least some non-linear and frequency distortion of the signal. Digital transmission does not introduce either of these distortions. Display Format Flexibility - In the analog systems, the transmission and display formats are coupled, and the display format is rigidly controlled by the transmitted signal. In digital systems, the receiver chooses the display format, and it can differ considerably from the transmission format. This flexibility is one of the key characteristics of the digital signals. 3

4 NASA s CURRENT AND FUTURE PLANS Project Overview Downlink video in digital format (SDTV) for STS-110 was received and distributed in the MCC (Mission Control Center) using DTV interface equipment developed by the Electronics Design and Development Branch (EV2) DTV Project. This interface equipment will handle future STS digital video downlink. Efforts are underway to procure more digital display and processing equipment. An SDTO (Station Development Test Objective) is currently underway that will allow HDTV to be downlinked live from the ISS. NASDA is sponsoring this project, and Rodney Grubbs is the NASA DTV Lead. It has been proposed that this SDTO should fly on STS-114, ISS flight ULF1. On ISS the HDTV video will be encoded as a Moving Pictures Experts Group 2 (MPEG-2), Digital Video Broadcast (DVB) compliant data stream. The data stream will have CCSDS (Consultative Committee on Space Data Systems) packets added and introduced to the ISS HRFM (High Rate Frame Multiplexer) as payload data. Downlink goes to both the JSC and the MSFC. The FEP at MSFC will add EHS headers to the data. It will be distributed via the PDSS to a TREK workstation in the POIC, tentatively in M103, SOA-E. The TREK workstation will remove the EHS and CCSDS headers and output the data on a serial interface. From there, it will be distributed as an encoded bit stream to NASDA. The data will also be decoded to HDTV for viewing and recording. NASDA is supplying the HDTV camera, flight encoder, ground decoders, recording equipment, and distribution equipment for MSFC. JSC Avionics is supplying the interface to the ISS communications system, which includes power conversion for the flight equipment, the CCSDS converter, and the interface to the HRFM. The MSFC is supplying the TREK workstation and integrating the distribution and recording equipment into the POIC and the media release point. System Test Overview In April 2002, an end-to-end system test was conducted utilizing the ESTL (Engineering Support Test Laboratory) facility at JSC. Cameras like the ones proposed for flight provided both live and playback HDTV signals. The engineering prototype of the flight interface was used to input data to the ISS communication system simulator in the ESTL The first test was a loop from the ISS communication simulator to the ESTL FEP. This test was successful. The next step will be to uplink to TDRSS and process the data stream through the entire ground system. This will be done using both the ESTL and the MSFC FEP. At this time no date has been scheduled for the test. This is likely to be the only full flow test of the system through TDRSS before flight. As such, it is important that the data for the test be recorded at MSFC so it can be utilized for further testing before the flight. The diagrams below show the flow for the test and the mission. NASA DTV Archiving Subgroup The NASA Digital Television Archiving Subgroup is evaluating possible archiving solutions for NASA video assets. Currently, NASA has video content media spread between all centers on volatile, aging analog formats such as U-matic 3/4-inch tapes. Recommendations of this group include the following: Standard definition video should be encoded at least MPEG-2 main level 4:2:2, 6 Mbps for computer video archive storage. The MPEG-2 encoder must be able to handle analog composite or component or SDI inputs. Higher levels of MPEG-2 are recommended for HDTV storage. Documentation accompanying the MPEG-2 file or metadata should have a minimum of 8 common database fields. The metadata text file must be linked to the MPEG-2 file. A centralized NASA video storage system and search engine will be more cost effective and user friendly. 4

5 HDTV ISS Multi-format System Communication Test Station Flight Side (4/1/02) (Courtesy of S. D. Holland, EV2, DTV Project Engineer) Station Downlink 1080P/I VTR SIGNAL GENERATOR HDTV Camcorder AJ-HDC27V HDSDI [720P] HDSDI HDSDI HDTV Camcorder HDW-700A w/ HDSDI Adapter [1080I] +120VDC 12V HDSDI Audio SEZ I LCD Monitor Station Flight Side SEZ DVBASI to CCSDS Packetizer / Audio / Pwr DVBA CCSDS Packets Alarm AES/EB 12V NTT HE1000 MPEG-2 HDTV CE ISPR APS / HCOR HRFM 5

6 HDTV ISS Multi-format System Communication Test Station Ground Side (4/1/02) (Courtesy of S. D. Holland, EV2, DTV Project Engineer) Station Downlink On-Orbit Test MCC Station Ground System TEST & VERIFICATION EQUIPMENT TBD DQM EHROCS ESTL FEP HEALTH & STATUS TELEMETRY Data smoother HD1000 MPEG-2 Decoder HD frame sync TBD HDSDI F/O Distribution interface F/O F/O PACK, 62.5, F/O EV2 CCSDS Station Ground Side ESTL HRFM DVBASI F/O Distribution interface HD VTR HD MON JSC F/O DISTIRIBUTION SUMMARY 6

7 Color analog television systems have successfully prevailed for last forty years. Following Japan s introduction of an analog HDTV system in the early 1980 s, the US and Europe eventually formed the Grand Alliance, which defined the all digital Advanced Television (ATV) Standard, including HDTV. Now, a new era of all digital systems has begun and HDTV has become a reality, with networks and cable companies partially broadcasting in HDTV. NASA has evaluated the use of HDTV and is in the process of developing and testing HDTV equipment/systems for Space Shuttle and Space Station usage. CONCLUSION The incorporation of HDTV will greatly enhance Space Shuttle and Space Station operations, and science activities. When it is fully implemented, HDTV will become indispensable to NASA and its International Partners. REFERENCES AND SOURCES The following books, articles, papers and web sites were used to prepare this paper: Video Engineering by Andrew F. Inglis and Arch C. Luther, McGraw Hill, NASA DTV Working and Archiving Subgroup STS-114 HD Downlink Status - Dylan Mathis, Imagery Working Group HDTV Glossary of Terms AES-3 Audio Digital audio standard output by the HDTV MPEG-2 Decoder 7

8 B Frame - Bidirectionally predictive coded picture. An MPEG term for a picture that is encoded using information from prior and subsequent I frame. Part of GOP. Chroma Color information within a television picture. Chroma is two channels of information, Primary Red and Primary Blue for HDTV, noted as P R and P B DA Distribution Amplifier Device used to provide multiple isolated outputs of a signal HDTV Encoder Device used to reduce bandwidth of HDTV digital video by compression using MPEG- 2 compression HDTV Decoder Device used to decode MPEG-2 data stream to HDTV DVB/ASI Digital Video Broadcasting/Asynchronous Serial Interface. Packet format of MPEG-2 data output by the HDTV Encoder 4:2:0 Encoding - Ratio of luminance to chroma samples for encoding video. 4:2:0 samples chroma at ½ the rate of luminance and skips chroma every other scan line of video. 4:2:0 is acceptable for distribution, news editing, and viewing, but not advanced post-production 4:2:2 Encoding - Ratio of luminance to chroma samples for encoding video. 4:2:2 samples chroma at ½ the rate of luminance on every scan line of video. 4:2:2 is considered full-bandwidth and is acceptable for advanced post-production. GOP - Group of Pictures Number of video frames an MPEG encoder codes as a group. The group cannot be interrupted without corruption of the video signal. High GOP allows lower data rates for a given quality of picture, but increases latency. HD-SDI High Definition Serial Digital Interface HDTV - High Definition Television, refers to 1920x1080 and 1280x720 16:9 picture formats. 1920x1080 can be interlace or progressive (will likely be interlace if used for flight) and is referenced as 1080i or 1080p. 1280x720 is always progressive and is referenced as 720p. I Frame - Initial Frame. MPEG term for first picture in a GOP. Contains information on every pixel in that picture. Used a basis for predicting motion in subsequent GOP. Interlace Scanning - Screen scanning format where the odd and even scan lines are alternately displayed during each vertical scan of a picture tube or display device. One full frame is displayed for every 2 screen scans. Each screen scan is a field. Luminance - The measurable brightness and contrast of a video image. Often referred to as the gray scale or black & white portion of the picture. MPEG - Moving Picture Experts Group - Refers to the digital encoding and compression system for motion video. NTSC - National Television Systems Committee - Color television standard adopted in P Frame - Predictive coded video picture. An MPEG term for a picture that is encoded using information from prior I frame. Part of GOP. Progressive Scan - Scanning method in which every scan line is scanned during each vertical scan of a picture tube or display device. A full frame is displayed with each scan. SDTV - Standard Definition Television - Refers to 640x480 and 704x480 4:3, and 704x480 16:9 television formats. Serial Digital Interface- Coaxial cable signal interface that transmits digital information in a single continuous bit stream, one at a time. 8