Ever wonder how broadcasters check picture transmission quality? Traditionally, they pay people to sit for hours watching video and rating its visual appearance subjectively. So I talked this week to Spirent Communications about a new automated system they have for testing video streaming on mobile phones.

The use of cell phones for audio and video downloads is becoming surprisingly popular. Qualcomm’s recently developed MediaFLO network got a lot of media attention, perhaps because it’s new outlet for media. Verizon and Cingular both struck deals with MediaFLO early this year.

And the demands of offer video to cell phones present challenges a lot different from broadcast or cable television–particularly when the cell phone user decides to watch the video at the same time as doing something else with the phone–which they are prone to do, much to the annoyance (I imagine) of the content providers as well as the network operators

Spirent’s mobile video testing

Spirent’s business, in general, is the testing and analysis of communications networks. They cover a wide variety of system (VoIP, Ethernet, IMS, etc.) but this blog focuses on a new system to test mobile phones accessing the MediaFLO broadcast network (discussed later in the blog).

According to Nigel Wright, Vice President of product marketing at Spirent, testing the quality of video on a mobile phone with human testers could take up to a week and be very expensive. This is a significant burden in a market where the public is always clamoring for the newest and most feature-rich cell phone (for the status of owning one, if not for the features themselves) and companies release new models frequently.

But a standard test specification developed by QualComm (TIA 1102, Minimum Performance Standards (MPS) for Devices) sets up parameters for automatic testing. Last week, Spirent announced that they were the first to provide a system called FLO1-ATS that offers fully automated testing for MediaFLO-enabled handsets, following TIA 1102.

FLO1-ATS is particularly useful during handset development. Spirent also provides tools for concurrent testing (where the user downloads a video and does other things at the same time on the handset). Spirent has less direct involvement in another common kind of analysis called interoperability testing (ensuring that devices and networks can do everything the standard requires).

Another Spirent tool, the Wireless Multimedia Analysis (WMA) module, captures video from the end-user’s handset in the lab using a digital camera. Spirent says they developed their algorithms during several years of experience with leading mobile operators. The tool measures end-to-end quality (as opposed to network statistics) by analyzing the video and producing a mean opinion score (MOS), which they’ve found matches closely to the average opinion score given by humans watching the same video. It also automatically assesses user experience through key performance indicators such as frame loss, blur, jerkiness, blockiness, and audio/visual synchronization (particularly important for lip sync).

Spirent also has solutions for field testing. If used in a moving car or public transportation system, the device can record locations from a GPS device and let the testers determine later the conditions at each location. When the test is completed, the device produces a quality report based on the stored video.

MediaFLO and the mobile broadcast business

When video began on cell phones, it was unicast. this gives the user maximum control over what she views, but of course is murder on bandwidth. As more and users simultaneously try to stream video, the load on the network load leads to service disruption.

MediaFLO, by contrast, is a broadcast system (FLO stands for Forward Link-Only). In fact, Wright told me it was developed by people who came from the broadcast TV industry. MediaFLO currently offers 20 channels. It’s a totally independent network with its own towers; the cellular network is used only as the uplink to transmit user requests back.

In the U.S., MediaFLO uses spectrum allocated earlier to UHF channel 55 (about 720 MHz). This is better spectrum than cellular (which is mostly in the 850/900/1900 MHz bands, or even higher). The UHF channel’s lower frequency allows wide coverage, like over-the-air TV, and penetration through walls, etc. It’s also regulated differently, the particularly important factor here being higher power.

(A month ago I talked to another company, Ortiva, which claimed to solve the problem without setting up a separate broadcast system.)

Unlike TV broadcasting, mobile broadcasting needs to coexist with other applications. A user may need to make a 911 call in the middle of a video, or just want to download a web site. This needs to happen without a noticeable loss in performance.

New mobile phones now contain two receivers, one for conventional cellular and one for MediaFLO. Power consumption has improved to the point where a cell phone user could view a video continuously for 4 hours (if that’s humanly possible) without recharging the battery. MediaFLO uses time division multiplexing to transmit each content stream at specific time intervals. So the MediaFLO receiver in the phone needs to power up only during the time period during which its needed content stream is transmitted. It sleeps for the remainder of the time, saving power.

Streaming video also has to deal with the variations in bandwidth due to the quirks of location, weather, and so on. MediaFLO can change the frame rate depending on the bandwidth quality, allowing graceful degradation of reception.

Wright compared MediaFLO favorably with the DVB-H system that has been adopted mainly in Europe. DVB-H sticks more closely to the over-the-air broadcast television standard, DVB-T. It can require twice as much bandwidth to deliver the same number of channels as MediaFLO. Moreover, the scheme used by MediaFLO for time interleaving of its data allows switching channels in around 1.5 seconds, closer to the experience of cable channel-hopping. This compares with 5 seconds or more for DVB-H.

Movies have adopted over the years to the reality that many viewers won’t see them in a movie theater; a lot of the big-screen effects have faded out in favor of shots that look good on home TV screens. Home TV screens have gotten larger, of course. But if the popularity of video on cell phones continues, it will put powerful new pressures on video makers, as well as the networks that transmit the videos.

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