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3G-SDI’s Many Advantages Serve Defense Video/Display Needs

Video interface technologies tend to advance so fast it’s hard to keep pace. Military system developers should examine the benefits of moving to 3G-SDI.


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One of the most daunting tasks for engineers is how to employ existing and proven technology while hopefully future proofing systems for technology upgrades. This is of critical importance to systems in the military market with air and naval systems having life cycles that can be in excess of 35 years. The problem is even more acute in deploying video imaging and display technology. Video image resolutions have been steadily increasing in size based on improving sensor/camera resolutions and increasing quality and resolution of LCD panels. Just in the past few years the video broadcast industry has moved from PAL (720x576 Interlaced) to HD720p60 (1280x720 Progressive) and then to HD1080p30 (1920x1080 Progressive) and future formats of WQHD (2560x1440) and UHD-1 (3840x2160) are on the near horizon. The bandwidth required to support these formats pose a challenge for selecting an interface standard since the size of the data is becoming exponentially larger.

Analog standards like VGA are willfully inadequate for today's higher resolutions. Digital video is the only choice, but which standard is the optimum choice? DVI, HDMI, DisplayPort and SDI (Serial Digital Interface) are the typical options when handling a digital video signal and many monitors support multiple input types. However, there are clear tradeoffs between each of them.

Back to Basics

To select the best solution, it is necessary to go back to the basics. Military systems require reliability, simplicity, expandability, and mature standards based technology. Looking at DVI, HDMI, and DisplayPort - all these are digital standards employing some form of SERDES technology. However, they all require multiple channels (connections) of serialized data. Thinner (lesser number of connections) cables are much preferred since cable thickness can drive the flexibility, weight, length, and ease of installation. Besides, to ensure video quality, HDMI usually can have a maximum length of 20 meters and DVI-DL (Dual Link) and DisplayPort can both be approximately 4.5 meters.

Resolution and audio integration are also important considerations. DVI-DL supports resolutions up to 2560x1600, but does not support audio. HDMI_2.0 and DisplayPort V1.2 can support 3820x2160 at 60 frames per second and support audio. Figure 1 shows a summary those different interfaces.

Figure 1
Multiple factors to compare amongst video interfaces—including supported cable length, resolution and audio integration.

While HDMI, DVI, and DisplayPort are more widely found and familiar in the consumer space, SDI is a more widely accepted interface standard for video distribution. It is a mature standard that was first adopted by the commercial video broadcast community but in recent years it has been incorporated in a number of consumer devices such as low cost HD video cameras. This is advantageous because COTS suppliers will have a larger ecosystem of SDI capable components and technology and therefore supporting longer life cycles will be easier.

Examining SDI Closer

Looking under the hood, SDI is 4:2:2 YCbCr format. Where Y is the luminance component and Cb/Cr are the chrominance components. YCbCr format is often preferred over RGB because of the efficiencies gained by sampling the luminance at twice the rate as the chrominance components. This subsampling creates a loss in color accuracy, but because of the way the human eye interprets data, the subsampling using a YCbCr system is much more effective in preserving quality than what is used in an RGB system.

There are a few variations on the standard, supporting increasing resolutions: SD-SDI (SMPTE259M) supports 640x480 60 frames/sec (fps), HD-SDI (SMPTE292M) supports 1280x720 60fpsor 1920x1080 at 30fps, and 3G-SDI (SMPTE424M) supports 1920x1080 at 60fps. New formats have been defined to support 2160p30 (6G-SDI) and 2160p60 (12G-SDI) with a resolution of (3840x2160) with frame rates of 30fps or 60fps respectively, but these formats are not yet widely adopted. Figure 2 compares the various SDI options. HD-SDI is currently the most widely adopted SDI implementation, but recently a push has been made to support 3G-SDI resolutions since they provide twice as many frames as HD-SDI at the same 1920x1080 resolution. These additional frames can be critical in a mission environment.

Figure 2
HD-SDI is the most widely adopted SDI implementation, but recently a push has been made to support 3G-SDI resolutions providing twice as many frames as HD-SDI at the same 1920x1080 resolution.

In addition to sending video data, SDI also supports embedded audio as well as ancillary data (ANC, which is also referred to as metadata). This allows cameras/sensors to generate and send all typical data types over a single standard. Another key benefit of SDI over DVI, HDMI, and DisplayPort is that SDI is usually transmitted over low-loss digital video grade RG6-syle coaxial cable. The benefits are compelling, SDI is a single connection cable-very flexible, minimal weight, and inexpensive connectors on each end which also lock. And since many legacy systems still using analog feeds already use RG59/RG6 cables, in most environments, no re-cabling will be required. The existing cable feed can be re-purposed and only the front and end products (SDI transmitter and receiver) will have to be changed to support SDI. Since it is a single connection there are no reverse insertion or mating issues. SDI can also be supported over optical fiber for extended reach applications.

Cable Length Advantage

Maximum cable length is also a clear advantage. SDI employs a NRZI (Non-Return-to-Zero Inverted) coding scheme that allow clock and data to be encoded together and minimizing residual DC components on the signal. This allows SDI cable lengths to be quite long. For example, 3G-SDI using Belden 1855P cable is capable of lengths of up to 40 meters. Using higher quality can enable lengths of up to 200 meters. This allows the SDI signal to be physically routed large distances on vehicles (for example, from front all the way to the back of a large vessel) with no concern for data integrity issues.

Ancillary data is also supported in the SDI standard. Data such as audio, close captions, timecode, and metadata. Metadata and timecodes are of particular importance in military and ISR applications since image sensor data must be timestamped and data about sensor positon must be transmitted in a synchronize fashion with the image.

Clearly, there are a number of benefits to employing SDI video interconnect format over other digital standards including DVI, HDMI, and DisplayPort. SDI cables, while simple coax with BNC type connectors on the ends, offer flexibility in installation, longer cable length and a locking mechanism that survives rugged environments. Sometimes, there are coax cables already present in many analog configurations Reuse of these cables saves time and money. Also, SDI cables weigh far less than HDMI or DisplayPort cables. All these advantages offer it as an attractive video alternative in the military environment.

Roadmap to 4k Support

Furthermore, the SDI standard has a defined technology roadmap to support 4K resolution and beyond. This allows engineers to deploy 3G-SDI for today's 1080p requirements with the ability to potentially support 2160p30 and 2160p60 sensor/cameras and LCD displays without having to modify installed cabling.

Users of EIZO Rugged Solutions' products are showing great interest in adopting 3G-SDI as the standard of video interconnect. Their expectation is that by developing products with high quality coax connection, they will offer future technology upgrades (such as 6G-SDI and 12G-SDI) without re-cabling. This future proofs their installations. Companies in the defense space including EIZO Rugged Solutions now offer products that support these xx-SDI standards. For example, the Tyton VS2-a low-latency, high-efficiency rugged H.265 (HEVC) video encoder with dual 3G-SDI inputs (Figure 3). The Tyton VS2 is a ruggedized small form factor box-level video encoding and streaming solution which can be used to take multiple SDI inputs, encode/compress the incoming data and distribute it over the network, either for recording, processing or display at a remote location.

Figure 3
The Tyton VS2 is a ruggedized small form factor box-level video encoding and streaming solution. It provides a low-latency, high-efficiency rugged H.265 (HEVC) video encoder with dual 3G-SDI inputs.

Another product is the Condor 4107xX which is a rugged conduction-cooled XMC graphics card that offers 2 3G-SDI inputs and 2 3G-SDI outputs. With dedicated video capture circuitry and a powerful AMD 8860 GPU processor, the card offers very low latency from the time of raw data capture to display on to the screen, including all the processing in between, including overlays. Moreover, this allows SDI to not only be used at the camera/sensor level, but also at the display/monitor level allowing computers to be 100 feet or more from the display monitor, something that cannot be done with DVI, display port or VGA. Though the use of SDI sensors has been the standard for years now, the use of SDI monitors in military vessels with advanced desktop environments has only recently begun with certain installations benefiting greatly from the simplicity and flexibility of SDI.

This is highly beneficial on larger craft where a desktop environment may have to be rendered or split/mirrored a large distance away from the source with very low or no latency. Previously, installations would opt to compress and stream these desktop feeds to all needed locations on the vessel with an induced latency, but with these desktop feeds and monitors being natively SDI they can instead be hardwired throughout the installation.

SDI Perfect Military Fit

Benefits of SDI and its cabling system fit very nicely into the military environment considering the requirements such as very long product life cycles, upgradeability, ruggedness and responsiveness (low latency). Though previously product availability would define what cabling and interface should be used, in recent years with the large variety of rendering, monitor, and sensor options now available, there is no reason not to shy away from SDI for video handling and distribution throughout an installation.

EIZO Rugged Solutions
Altamonte Springs, FL
(407) 262-7100