Going Mobile: An Issue of Video Quality and Bandwidth
Digital Video Recorders (DVR) and Home Theater PC’s (HTPC) allowed the migration from “prime time” to “my time” as we became accustomed to time-shifting our entertainment and viewing it at our convenience. Place-shifting, introduced through products such as the Slingbox from Sling Media, gave us the ability to access our preferred and subscribed-to entertainment wherever there was Internet. The freedom to view what we want, when we want, where we want became an expectation. Tablet PC’s and Smart Phones connected to cellular networks turned this expectation into a demand for Going Mobile, and that’s when the wheels began to fly off back at the old cell tower.
Today’s promise is that LTE technology in cellular networks and the next iteration of MPEG compression, H.265/HEVC, will bring a smooth seamless video experience to the mobile user, but will it? Here’s an article discussing Verizon hitting full LTE bandwidth capacity by 2013.
In wireless telecom, Long Term Evolution (LTE) is the name given to the interim technology that migrates from aging 3G networks, designed to accommodate voice, texting, and minimal Internet browsing to the future 4G cellular networks. These networks are designed for much higher data rates required by the ever increasing consumption of video. Marketeers take liberty with the terminology to make it sound like 4G is here today,but it’s not. The authority on such matters, the International Telecommunication Union (ITU), set a peak data rate of 100 Mbit/s to be considered 4G. LTE, while simplifying the air-interface of the cellular network by migrating to an all IP-based interface, offers peak data rates limited to tens of Mbit/s.
One of the most comprehensive analyses to date of LTE’s ability to provide a satisfying user experience for mobile video comes from Motorola’s white paper titled Opportunity and impact of video on LTE Networks published in 2009. This paper developed arguments for the number of video streams that could be transmitted per sector at any given LTE cell tower based on heuristic data for video quality as viewed on various display sizes, and assuming block-based H.264 compression levels. For instance, according to Motorola’s analysis, the minimum resolution for perceived high quality (HQ) video on an iPad-sized 9″ display requires at least 480i Standard Definition (SD) at about 1.5 Mbit/s using H.264 compression. Given the 2,048 by 1,536 pixel resolution of Apple’s Retina display, this is arguably too conservative. Nonetheless, using this argument, the maximum data rate capacity of a typical 20 MHz LTE cell sector would support less than 20 unique video streams. Similarly, that same LTE implementation would support less than 10 unique 720i High Definition (HD) video streams at 3.5 Mbit/s.
So, what conclusions can we draw from this 3 year old data, and what inferences can be made for today and the future? In an urban area with over 1 million subscribers such as Philadelphia or San Diego, the average number of subscribers per cell-site sector is well over 300. Motorola’s estimates tell us that the bandwidth capacity of an LTE network would be exceeded if more than 7% of those subscribers in any given cell sector attempted to view SD video on their mobile device. Assuming that other subscribers are likely to be talking, texting, or surfing at the same time in that cell, this number is probably much less than 5%. This points to the relatively poor performance commonly experienced today when trying to watch quality video in a mobile environment.
What impact will H.265/HEVC, the next generation of block-based video compression, have on the mobile experience? This is a fairly linear system, so if we assume H.265/HEVC can achieve a 50% improvement in compression over H.264, then there would essentially be 50% less data for a given video quality, so the maximum number of unique video streams per cell site sector would simply double. Rather than 5% of subscribers maxing out the capacity of a cell sector by simultaneously watching unique SD video streams, the number would go to 10% with the introduction of H.265/HEVC into the LTE network. This is still far from the mobile experience consumers are demanding.
All of this points to the fact that watching what we want, where we want, when we want in a truly mobile world is a dream for the future. A future where true 4G networks bring an order of magnitude greater bandwidth, and model-based compression methods, such as EuclidVision, allow higher quality video at significantly lower data rates.
MacRumors notes in this article the difference in speed from the 3rd Generation iPad to the new iPad due to adopting LTE .