Transmission Processes for Cable Networks

Summary

The cable industry in the United States is maturing into a fiber-based, two-way and digitally capable world, able to deliver broadband digital-video and data services. Digital compression and transmission technology for video delivery has an impressive development track record. The theoretical possibility of two decades ago has become vital for telecommunications.

The cable industry in the United States is maturing into a fiber-based, two-way and digitally capable world, able to deliver broadband digital-video and data services. Digital compression and transmission technology for video delivery has an impressive development track record. The theoretical possibility of two decades ago has become vital for telecommunications.

Cable Television Laboratories, Inc. (CableLabs), is a research and development consortium founded in May 1988 to ensure the proper development of technological initiatives for the cable television industry. CableLabs is supported by cable television system operators in the United States, Canada, and Mexico. CableLabs is the entity which has as its underlying function to manage technology for the cable industry's advancement The current portfolio of research and development projects for CableLabs includes advanced television testing, refining the development of cable network architecture, and improving the consumer electronics interface. Clearly, the digital compression and digital transmission are the key tools in those projects.

Today’s cable network is migrating from the traditional tree-and-branch topology that was originally designed for point-to-multipoint video entertainment to a distributed star, tree-andbranch topology. The new architecture has a robust, dynamic capability for a wide range of applications beyond video entertainment. The migration of cable systems to 1 GHz and the introduction of multi-channel pay-per-view also suggest the need for mass storage video sources from a centralized, shared facility. The regional hub is a centralized shared facility that serves many functions. The regional hub will serve as an access point to digital transmission networks, including synchronous optical network (SONET). This keeps the interconnection point at a higher hierarchical level and allows the cable industry to provide proprietary protocols within the cable infrastructure if it so chooses. By using a fiber node, we may be able to eliminate the active components in the coaxial part of the network to the home. This issue has a special significance for digital transmission deployment.

I was asked to comment on digital 'transmission processes for cable networks.’ This is not an easy task to be accomplish in twenty minutes of my address. There are many issues and topics. Let me focus on two points only. The first one — how we got to this digital world on cable, and the second — cable digital modulation, the current status.

Digital compression and digital transmission were coming to cable, and CableLabs was involved in since early efforts to help make these technologies successful. We contribute to the FCC selection process of the HDTV standard. In parallel, CableLabs issued the original (1991) request for information (RFI) on digital video compression and satellite/cable transmission.

The main thrust of CableLabs’ effort is geared to the cable system portion of the cable distribution network, but CableLabs has also examined other transmission systems that are part of the overall end-to-end cable delivery network, such as satellite, terrestrial fiber optic long distance and regional hub links.

The right approach to consider transmission processes for cable network is within the OSI framework. We usually discuss a general topic of transmission processes, but true focus is continuously changing. In the early phase, the attention was on digital compression. Now, the attention is shifting toward issues related to physical and data link layers of the OSI framework. At the same time, more interest is being expressed in transmission protocols and data packaging. The consideration of cable digital modulation within the OSI model calls for industry standard.

Digital compression and transmission requirements for cable networks are defmed by business objectives and basic functionality of the system, as well as by results of characterization of physical cable plant. There are three key choices for high density modulation schemes for digital data on cable: OFDM, 2^2M-QAM and 2^M-VSB.

CableLabs is currently conducting research and field testing to characterize the transmission quality of existing cable systems, with particular attention to the impairments that can cause trouble for digital signals.

I am delighted and honored to be invited to address this gathering of experts in the field of digital television and radio at a moment when technical advances in digital compression and digital transmission systems are announced almost daily and deployment of digital compressed video delivery for satellites has already begun as well as is being expected to commence shortly in the cable television systems for video delivery in the United States.

One of the most remarkable aspects of recent advances in technology is the convergence of telecommunication industries. The cable industry in the United States is maturing into a fiberbased, two-way and digitally capable world, able to deliver broadband digital-video and data services. These trends open opportunities for technical partnerships in delivery systems and for exciting new digital services. Digital compression and transmission technology for video delivery has an impressive development track record. The theoretical possibility of two decades ago has become vital for telecommunications.

Today, I am proud to speak to you on behalf of the CableLabs and the cable industry in the United States, which is forerunner in the efforts to bring digital compression and transmission deployment for video delivery by cable networks. What was impossible a few years ago becomes reality today. And I would like to share with you some accomplishments by the cable industry, especially in digital transmission on cable systems and networks.