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The July 10, 2008 Issue Provided by System Dynamics Inc.
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Cable Show 2008: More Bandwidth Magic--Imagine Communications

The rabbits keep getting pulled out of the magician's hat. Well, it's not rabbits, it's bandwidth--and once again, a start-up company offers MSOs another way to multiply the effectiveness of their spectrum.

To increase the plant's carrying capacity, operators can already choose between a wide variety of technologies, including

  • reducing the number of homes on each node ("spatial reuse");
  • reducing the number of channels allocated to analog services ("analog reclamation") including completely eliminating analog ("all digital");
  • using statistical multiplexing to avoid broadcasting channels when nobody is watching ("switched digital video");
  • upgrading the plant to 860 MHz or higher ("spectrum expansion");
  • overlaying the existing bandwidth with additional spectrum ("spectrum overlay");
  • changing video encoding from MPEG2 to MPEG4 AVC ("advanced video compression");
  • bonding channels to increase the maximum data rate for high-speed data services ("DOCSIS 3.0"); and
  • using higher-order QAM ("advanced modulation ").

We've written about these techniques many times--"For More Information" at the end of this article provides pointers to our earlier articles. Many of these techniques are now well along in implementation, including SDV (Switched Digital Video), analog reclamation, and DOCSIS 3.0.

At this year's show, we talked with a new entrant offering a clever approach to video processing and statistical multiplexing.

Imagine Communications

Jamie Howard --> Click for larger pictureFor an early-stage company, the staff of Imagine Communications has lots of experience with cable bandwidth. At the show, we met with President and CEO Jamie Howard, whom we've known for some time in his earlier roles. Jamie, who joined Imagine last September, was COO of BigBand Networks, the pioneer of switched digital video (which we first wrote about six years ago). Imagine's co-founders Doron Segev and Ron Gutman were senior members of BigBand's R&D team in Israel--where Imagine's R&D is also headquartered.

Imagine's products incorporate several techniques to get higher video compression without losing quality: separating video processing and multiplexing; coding video with interchangeable compressed elements (ICE); moving statistical multiplexing to the edge of the network; using variable bit rate (VBR) in all multiplexes; and using a video quality measurement algorithm to maintain consistent perceived quality.

Imagine's key idea is to separate the video processing from the statistical multiplexing. They do this by creating multiple versions of video frames in the video processor. The same video content is created with several different compression levels--these are the interchangeable compressed elements. This takes a lot of processing power, but is done just once for each stream in the headend.

The VBR-based ICE statistical multiplexers (StatMuxes) are placed at the network edge, along with QAM devices, just before distribution to fiber nodes. The edge StatMuxes assemble the multiplexed stream by selecting the optimal compressed element for each stream according to the amount of bandwidth available at each point in time. Since several versions of each video frame--each with different compression levels--are already available, this requires comparatively simple processing.

This approach is more bandwidth efficient than traditional techniques, which either create the VBR muxes as part of video processing, or use constant bit rate (CBR) multiplexing to assign fixed bandwidth to each video stream.

Imagine's video quality subsystem incorporates a video quality measurement algorithm claimed to "accurately emulate the human visual perception system". This is used to optimize the compression of each frame, by assessing its video quality to assure that lower bit rate coding will not impact perceived video quality.

Imagine packages these technologies into several product solutions. The Broadcast System uses standard definition and high definition broadcast processors to create ICE video streams, and ICE multiplexers to create multiplexes at the edge. Imagine claims operators can get 50% more video streams in each QAM--15 SD streams or 3 HD streams, instead of 10 or 2--without loss of perceived video quality.

These same techniques can be applied to SDV and VOD. Imagine's architecture permits the use of VBR rather than CBR for the multiplexed streams, with substantial gains in bandwidth efficiency.

Imagine Architecture --> Click for larger picture

In a white paper VBR/StatMux for Digital Broadcast, VOD and SDV, Imagine argues that their solutions are the most cost-effective way for operators to gain additional capacity for HD broadcast and on-demand services. The paper claims other approaches require more capital expense and time, replacement of existing set-top boxes, and more disruption to consumers.

Given the background of Imagine's key players, these claims seem credible. We're waiting to see how operators respond. No trials have been announced, but we'd be surprised if major operators aren't already kicking the tires to find out.

For More Information

We've been writing about "cable's magic tricks" for nearly seven years:

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