3/24/2013 12:33 AM
It has always seemed rather ludicrous to write off mobile video in the light of its litany of failures over the decade or so since the first trials took place. It was only a matter of time before the allure of mobility would extend to TV, waiting for a combination of device platforms and network bandwidth to be capable of rendering video in sufficiently high quality. Then, but only then, would compelling content become available over mobile devices.
It was the arrival of smartphones and tablets that created a consumer groundswell behind mobile video that has left mobile operators struggling to cope, but this has been led by WiFi access inside the home, where content rights issues are more favorable and Quality of Service easier to provide. This left mobile operators struggling both to keep up with consumer demand for video services on the move outside the home, and to cope with the deluge of traffic being generated. It has also put traditional pay TV operators under pressure to provide mobile access to their services from multiple screens, which they can readily achieve via WiFi in the home, but often need a cellular partner to do it outside in order to fulfill the service via the SIM card. This is all compounded by uncertainty over how successful emerging 4G mobile services based on LTE (Long Term Evolution) technology will be at delivering HD video on a large scale.
The answer, to that last question at least, is not too hard to find. LTE represents a huge advance in terms of spectrum efficiency and support for multimedia content over the preceding 3G that still dominates global services in most countries. But it does not do enough on its own, and cannot because radio spectrum is a limited resource.
Fixed networks based on fiber have effectively limitless capacity given the inherent efficiencies of encoding data over light via dedicated channels. The latest Ethernet over fiber technologies can transmit data at up to 100Gb/s over a single multimode fiber channel. Then use of DWDM (Dense Wave Division Multiplexing) technologies enables 160 of these channels to be carried on a single fiber using current transponder technologies, with no theoretical limit on the number that could be supported in future. This means just one fiber can now transmit at up to 16Tb/s, making it easy to see that backbone capacity will not be a constraint on future broadband growth.
The backhaul issue is not that fiber lacks capacity, but that it is often not available and is very expensive to deploy, but gradually it will not be. Radio access spectrum, though, is a very different matter, because there is no scope for techniques equivalent to DWDM, and barring some totally unexpected technical breakthrough, there is only potential for incremental improvements from now on in bit rate per unit bandwidth. This means that there are only two ways to scale mobile networks for video, to make cells smaller so that spectrum is reused more, increasing the number of subscribers that can be supported in given area; and by deploying multicast or broadcast on top of the underlying unicast transmission.
This is really an old story that has been revived by the arrival of real mobile video services driving up consumer demand. Many operators are looking to backhaul onto fiber-based broadband infrastructures via WiFi, but they are going need to address the RAN (Radio Access Network) capacity issue as well. This issue has reared up recently, with the DVB putting the case firmly for broadcast as the only long term solution for mobile video, irrespective of the RAN technology.
The DVB’s Executive Director Peter Siebert recently insisted that spectrum alone will not be enough, and that while unicast delivery is ideal for long tail content such as typical YouTube views, for big events like live soccer championships or elections, broadcast is far more efficient. Then the content is only delivered once within each 4G cell, even if there are many people watching. Broadcast would also be suitable for distributing commonly consumed news and information services, including weather bulletins, or even music and software, effectively trading device storage for spectrum.
LTE broadcast evolved to address this requirement, based on the evolved Multimedia Broadcast Multicast Services (MBMS) Standard, or eMBMS. For 3G, MBMS was developed to support point-to-multipoint distribution for broadcast to all cells, or multicast to selected radio cells in a given cellular network. But it was never deployed commercially, and it was one in a long line of failed mobile broadcast technologies.
But then, eMBMS came along as an upgraded version for 4G/LTE, bringing several key improvements. Rather than requiring ring-fenced spectrum, it now enables bandwidth to be reserved just for a session and then immediately released when it is no longer needed, in accordance with traditional multicast principles, if not operating in quite the same way. MBMS, and also earlier failed mobile broadcast systems such as MediaFlo from Qualcomm, required dedicated resources, making it harder for mobile operators to meet customer demands for anytime, anywhere video consumption.
Qualcomm itself has recognized this, and has been totally undeterred by the failure of MediaFlo, arguing that it was partly a case of being before its time. As the world’s largest maker of mobile chips, Qualcomm is well placed to stir the market and has been quicker than many operators to spot the emerging need for mobile broadcast. It has now embedded video acceleration into its Snapdragon mobile SoCs (System on Chips) that go into smartphones, tablets and laptops for both WiFi and LTE, along with support for eMBMS, so that the devices can receive multicast transmissions. With support for HEVC (High Efficiency Video Coding) – itself another crucial step by doubling compression efficiency over H.264/MPEG4 – these chips are going to galvanize mobile TV.