Bountiful spectrum makes video a WiMAX fit, but there are limits.

The aura around WiMAX has become overpowering of late. Anything that can be ascribed to an access technology has been ascribed to WiMAX: the bridging force of the digital divide, broadband anywhere, Wi-Fi on steroids. Proponents would have us believe WiMAX can do everything — and the latest feat they attribute to it is the ability to be the vehicle for delivering next-generation TV services.

That notion, however, may not be as far-fetched as it seems. While it's unlikely WiMAX operators such as Clearwire and Sprint will launch multichannel linear TV services in the model of the cable providers, satellite companies and now the telecom service providers, TV and video services clearly have a place in the new WiMAX business model. WiMAX operators are breaking from the old cellular models that created the “mobile Internet,” embracing WiMAX as a means to take the traditional Internet mobile. The difference is subtle, but the former carries with it notions of walled gardens, mobile-optimized content and managed content services, while the latter is the plain Internet — albeit uprooted from any static access line. That means customers will use the WiMAX broadband connection as they would any fixed broadband pipe. And following Internet trends, that means they'll consume video by the gigabyte.

“Look at the number of people who are connecting over wireline today; it's fair to say that broadband users will be doubling their traffic in the next few years, and much of that increase will be driven by video,” said Scott Richardson, chief technology officer of Clearwire. “We already know the baseline expectations we have for WiMAX.”

The advantages of WiMAX as a means of TV delivery aren't necessarily technological ones, though its high spectral efficiency and flat IP platform certainly are benefits. What WiMAX has that cellular technologies don't is gobs of spectrum. As Clearwire and partner Sprint roll out their nationwide Xohm network next year, they will have a combined average of 90 MHz of spectrum in most of their markets, giving them a lot of bandwidth with which to play. Having that kind of spectral capacity, WiMAX operators can deploy 10 MHz and even 20 MHz channels, all of which can support the massive bit streams of high-resolution video. Compare that to the 5 MHz channels allotted to UMTS or the 1.25 MHz channels of CDMA's EV-DO. Even Qualcomm's MediaFLO, which can pack up to two dozen channels in a linear broadcast stream, is still limited to the 6 MHz of spectrum that Qualcomm holds in most markets and to quarter video graphics array (QVGA) resolution — the size of a YouTube video.

Richardson said Clearwire's own internal analysis has found that 30 MHz of spectrum is enough for an operator to support the high video demands of normal Internet usage, but with 50 MHz of spectrum, that operator can layer on DVD-quality TV. With 70 MHz of spectrum, high-definition (HD) TV comes into play.

WiMAX isn't just being discussed as the means for delivering TV to the small screen of a handheld device or laptop, but as a full-fledged video delivery technology to the home. If a WiMAX network can deliver a broadband stream to a desktop gateway, it can deliver it to a set-top box, substituting for the traditional broadcast, cable and satellite pipes, said Kay Johansson, chief technology officer of MobiTV, which is conducting video trials with Motorola over Sprint's WiMAX network in Chicago. In fact, a WiMAX network can be configured to deliver the appropriate video to the appropriate device, sending QVGA to a handheld and HD to a digital TV. Just as WiMAX breaks down the barrier between the home network and the WAN, Johansson said, it can just as easily destroy the distinction between TV in the home and mobile TV.

“It's a user-centric model as opposed to a device-centric model,” Johansson said. “WiMAX has the potential to be the TV delivery mechanism for all of these types of devices. You can put WiMAX in the set-top box, into the laptop and into the phone.”

The WiMAX Forum has already begun exploring TV technologies in its infrastructure and applications working groups, and Mo Shakouri, forum vice president of marketing, said he expects a video delivery specification to be ready for the next release of WiMAX. Interest in the technology isn't just limited to the traditional carriers, and it's probably no coincidence that Comcast has joined the WiMAX Forum. As for the vendors themselves, many of the infrastructure manufacturers have begun working on multicast technologies that would deliver video more efficiently over the backhaul and access parts of the networks. But it's on the device side that much of the work to enable video is being performed.

The device landscape for WiMAX will be vastly different from 3G. The cellular market has always been driven by a single application, voice, which has served as the lowest common denominator against which all handsets are built. While there will be voice-over-IP (VoIP) services over WiMAX, the fundamental service offered to WiMAX devices will be data and multimedia. All devices are being built with that expectation in mind, said Steve Bell, senior director of products and business operations for Motorola's WiMAX devices unit.

At WiMAX World in Chicago, Motorola demonstrated a prototype handset that streamed a DVD-quality movie directly to a digital TV, using the phone's processor to render the movie. It may seem like an odd application, but Bell said that kind of capability is exactly what WiMAX was intended to support. By removing the access line from a fixed location, the device serves as a way of transporting a broadband connection from place to place, just like an iPod allows a customer to transport music. A single device could be used with various docking stations to deliver streamed music to a stereo, streamed video to a TV and maps to a vehicle navigation system. WiMAX devices can't just support the network connection, Bell said, they have to power all of the applications that connection will be used for.

“With WiMAX, the pipe isn't the problem,” Bell said. “So we've really moved the choke point from the pipe itself to the backhaul and processing power of the device.”

But those video capabilities come at a cost. WiMAX can support high-capacity video streams, but that doesn't mean WiMAX is the most efficient way of delivering multichannel video. Video is an enormous bandwidth hog. QVGA alone sucks up 300 to 500 kb/s per channel. Higher resolutions require exponentially more bandwidth. A DVD-quality stream would demand 3.5 Mb/s per channel, while an HD stream would eat 15 to 18 Mb/s — basically the entire capacity of a 10 MHz WiMAX sector. WiMAX spectrum may be bountiful, but it certainly isn't infinite. Even with 100 MHz of spectrum, a carrier could devote the majority of its frequencies to broadcast channels and come nowhere near the hundreds of linear channels offered by a local cable provider.

Deploying any kind of linear video architecture on a wireless access network immediately runs into the problem of scale, said Omar Javaid, senior director of business development for MediaFLO Technologies, the Qualcomm division dedicated to broadcast and multicast video. Qualcomm's MediaFLO is designed much like a traditional TV broadcasting system, using a few big towers and high-powered transmitters to blanket an entire city. Doing the same with WiMAX would require replicating those broadcast streams at every base station site and then dedicating an enormous amount of spectrum to transmit relatively few channels. The alternative is launching a unicast TV network, which could feasibly support any number of channels. But unicast requires delivering a separate video stream to each individual user, eating up an entire channel's worth of bandwidth for every customer watching a program on the network, Javaid said.

“What people want is a proper multichannel experience; they want linear video,” Javaid said. “If you have a popular mass-market media like TV, it has scale to millions of devices.” It's not that WiMAX or any other broadband wireless network doesn't have a place in TV, Javaid said, but it's role is more that of augmenting technology, providing premium video-on-demand (VOD) and interactive TV services rather than core TV content.

WiMAX vendors, however, are trying to split the difference between unicast and broadcast, creating hybrid multicast technologies that work in both unicast and broadcast modes. Just because a cable or satellite service offers 300-plus channels doesn't mean everyone in a given neighborhood is watching those 300 channels simultaneously. In a WiMAX network with hundreds of base stations, there will only be a limited number of people watching TV at any given moment, and several of those people are likely watching the same channel.

A multicast network would broadcast only the programs being watched, sending a single video stream for each channel. For instance, 10 people in a sector could be watching a football game, while one person is watching the Home Shopping Network. The network would multicast the game to those 10 people over a single channel and unicast HSN to the lone subscriber. The result is that 11 people would use the spectrum resources of two channels rather than 11 channels.

Multicast has its issues, too, however. There will be occasions where a large number of people will be on the network watching a multitude of channels, highly taxing the network's resources — something a broadcast network transmitting all channels simultaneously would not encounter. Several operators have enough spectrum to build in a buffer to handle those contingencies, but the question then becomes whether using that capacity for other services wouldn't be more profitable, said Rick Keith, director of strategy for WiMAX networks at Motorola.

“I can send to millions of users, groups of users or a single user, but the data consumed on the network is roughly the same no matter which format I use,” Keith said. “The question is what kind of revenues I'd collect in each case.”

Duplicating a cable company's many channels is probably outside of WiMAX's purview, but the technology could easily play with others. Satellite or terrestrial broadcasting could be used to provide core linear content, while WiMAX provides interactive functions and high-dollar VOD services.

“The plan isn't necessarily to compete head-to-head with cable, satellite or fiber/DSL services,” Clearwire's Richardson said. “We're going to continue to support the use case of people watching video over the Internet, but we're also looking into managed TV services.”

Those managed services could range from a carrier-branded downloadable video service to a partnership with a cable provider to mobilize its wireline programming. WiMAX could be used as a transport technology to time-shift a popular program a few hours later or place-shift live TV overseas. It can be used as the upstream component in an interactive advertising campaign, allowing customers to “click” on what would normally be a static TV ad to access more information on-screen or sign up for a promotion. It can even be used for community TV functions, which allow people in different places to watch TV together in a virtual lounge where they can communicate via VoIP.

The one caveat in all of these scenarios, however, is that the customer or the content provider will need the operator to do all of these things. Clearwire and Sprint envision WiMAX as an open-access network, replicating the free-for-all world that exists in wireline. What's to prevent Apple's iTunes, Comcast or Netflix from setting up shop on a wide-open WiMAX network to sell their video wares independently of the operator? That's a question operators will have to address soon, said Peter Jarich, research director for mobile networks infrastructure for Current Analysis. If they shut out independent video providers, then they won't be fulfilling their promises of an open mobile Internet. But if they allow video providers to run roughshod over their airwaves, they could drain massive amounts of spectral resources from their networks.

“Are we looking at WiMAX as a great way to access the Internet?” Jarich asked. “If we are, then who cares? People will go to YouTube on the WiMAX network just like they do on the regular Internet. But if we're looking for WiMAX to offer more than just access to the Internet, then it comes down to the question of business models.”