With the birth of 3Gb/s, various technical issues arose that would take advantage of the extra bandwidth, yet still be compatible with systems limited to 1.5Gb/s. SMPTE standards were developed, describing three different mapping schemes for transporting uncompressed video including ancillary data such as the audio data, the audio control packets, the payload ID, the time code, etc., into this new SDI interface running at 3Gb/s. These are defined as Level A, Level B Dual Link (B-DL) and Level B Dual Stream (B-DS). (See Table 1.)
Level A carries one 1080p video signal. Level B-DL is formatted in the same manner as described above for building larger, more cost-effective, high-quality production systems. Level B-DS is able to carry either two different 720p or 1080i signals, or one left and right frame-aligned pair of 3-D TV signals running at 720p or 1080i.
Although these mapping schemes appear straightforward, it is important to ensure the streams are properly tagged, as many devices are not compatible with all three levels. Additionally, we can’t forget about the embedded audio streams, especially in Level B modes. Be sure you know which streams you are actually using and modifying.
Cabling is also an important consideration. In SD infrastructures, cable lengths over 400m are typical. 1.5Gb/s infrastructures have a shorter length of typically 150m, with the latest technology providing up to almost 300m. For 3Gb/s, the length is typically 80m, with a maximum 180m made possible by using the latest technology. These cable lengths are dependent on the cable type and equalizer technology.
Fiber-optic technology is used when longer cable runs are required in a 1080p plant. Fiber is often thought to be highly complex, but this is far from the truth. IT usage of fiber has advanced the technology, and broadcast can tag on these improvements.
Additionally, a technology called small form-factor pluggable (SFP) now allows for deciding on-the-fly whether ports on routing switchers will use optical fiber or coax cabling. In this mixed-mode environment, both optical fiber and coaxial-type interfaces are used depending on the system design, which is typically decided on cable length requirements. (See Figure 1.)
For future-proofing plants, 3Gb/s certainly does the trick, and many infrastructure products are 3Gb/s-ready now. Some simply need software upgrades and have device control parameters set for various uses. (See Figure 2.) Notice for 3-D TV, there are a couple of options to bind inputs and outputs together depending if running dual stream or combined. For future 4K considerations, different options are available for binding together two (dual) or four (quad) ports for different 4K frame rate options.
In summary, moving to higher quality across the baseband workflow is possible today by using image formats such as 1080p. Building a plant based on 3Gb/s infrastructure products is a cost-effective way to keep your facility up to date. By eliminating the video scaling and deinterlacing technologies that cause artifacts in the video image before distribution into the home environment, broadcasters can follow the price curves of IT fiber-optical technologies, future-proofing their facilities with 3Gb/s and bringing higher quality into the home.
—Stan Moote is VP Business Development, Harris Broadcast, and Randy Conrod is Product Manager — Digital Products, Harris Broadcast.