Decisions, Decisions: Facing The Technological
Challenges Of Mobile TV
by Martyn Green
To find out about the challenges facing broadcasters and others seeking to get involved in providing video/TV content to mobile phones and PDAs, Hong Kong-based Martyn Green talked to Taiwan Television's Technical Director, Charlie Chang, and Raymond Lin Ray-rong, Deputy Section Chief, who work in the station's Digital System Section, in Taipei.
Taiwan is just one of a number of countries that are currently looking into the idea of using DVB-H technology to broadcast short TV programs to handheld devices like mobile phones and PDAs -- possibly later this year.
But, with DVB-H, DMB-T, T-DMB, etc, all the competing systems -- not to mention the confusing acronyms -- may seem quite involved, making broadcasters unsure where to place their bets.
However, Taiwan Television's Charlie Chang, Technical Director, Digital System Section, summarizes, "Basically, there are two groups: compared with DVB-H, South Korea's T-DMB has a lower bandwidth, meaning less data can be carried. However it can provide video as well. On the other hand, compared with DVB-H, China's DMB-T has a higher bandwidth, so more data can be carried, and the video is for television."
He continues, "Taiwan is using DVB-T for DTV broadcasting, with DVB-H currently the standard for mobile devices. However, Korea's DMB-T system has been introduced to Taiwan, although so far there have been no significant developments with this. Since radio stations here will eventually move to DAB, with DMB-T being based on that environment, radio stations will probably be among those most interested in this system."
But, from the telecoms side, with 3G, video usage is often limited to a maximum of about three minutes because it is a one-to-one system provided by telecoms operators. The bandwidth is limited by the basestation transmission capacity and, if there are many users, they will quickly tie up all the bandwidth.
DVB-H, on the other hand, works as "one-to-many," broadcast by a TV station. One can make a comparison with computers connected to routers -- with 3G there is a limited number of people who can log on at any one time, but with broadcast TV, as many people in one area want to watch, can do so.
Unlike TV streaming via 3G, DVB-H doesn't really eat up much bandwidth. It should also be a lot cheaper investment -- some figures put the cost at only about 10% of what was spent on starting up GSM.
Chang agrees that is true, pointing out, "GSM is effectively 2.5G and doesn't have the capability to provide video. Only 3G can do that. With a GSM phone, it can use the GPRS network for the return channel so it could provide interactive service, but it cannot provide video, like 3G's video conferencing."
So, faced with a variety of competing systems, what are the current technological challenges for mobile TV in Taiwan? Says Taiwan Television's Raymond Lin Ray-rong, Deputy Chief, in TTV's Digital System Section, "The fact is that there is more than one possible type of delivery method. The 3G system is in competition with DVB-H, and Taiwan may well end up having both, because telecom companies will want to promote their own services, as they have already built the infrastructure. But broadcasters also want to provide a service to mobile phone users, using their own infrastructure.
"We believe that with DVB-H decoders built in to handsets, the system will have several advantages over 3G. But the telecoms companies probably won't want to give up their service. And the problem is, right now, you need different handsets for the two systems, although they will probably be about the same price. However, 3G has been in the market longer." (There was a few days trial of DVB-H by Taiwan's China Television Service, CTS, back in July last year, with Nokia 7710 handsets provided by the company.)
The main advantage with DVB-H is that, unlike 3G (which can provide two-way video conferencing, but is limited to a few people in one area), it is broadcast, which means many people in the same area -- like a football stadium -- can receive it.
However, a disadvantage with receiving TV on mobile phones is that it can take some seconds (5 - 15) to change channels. To make it change more quickly would put a higher drain on the battery, because decoding another channel takes a significant amount of power.
Says TTV's Chang, "It would probably be good if DVB-H and 3G could co-exist as complementary technologies, if mobile phones and PDAs had the capability to handle both systems, but maybe not everyone would want to pay for that."
As regards technical problems for the broadcaster, Lin says, "It is not so difficult or expensive to modify the transmitter headend and some modulators, to provide DVB-H. It would probably cost NT$10 million to set up a new station but only about NT$1 million for us to add a new modulator." [About NT$33 = US$1.]
"The point is, with broadcast TV, we are not limited to three minutes, or by the number of number of mobile viewers in a certain area. Also, if a viewer uses 3G to see the content, he is charged by the time he watches, but with DVB-H, it is probably going to be free. The only cost is to the battery. However, since DVB-H uses 'time slicing,' it reduces the mobile receiver's battery consumption, so it can operate for longer, since the decoder won't decode all the service stream, only the program selected."
In Taiwan, Chang says, DVB-T uses 16QAM, while DVB-H uses only 4QAM, so there is far less information being sent out. "The reason only 4QAM is used is not because with tiny mobile phones, or PDAs, there is only a small screen, needing less information, but to avoid the Doppler effects when reception fails at higher mobile speeds. A 4QAM signal is better for receiving on a mobile unit."
So, if DVB-H seems to have real advantages over 3G -- viewers are not paying for the time, it is free transmission, the battery won't drain as fast -- why would anyone buy 3G?
Lin points out, "There are other things 3G can do, like surf the web, and video-conferencing. However, with 3G the bandwidth is limited to 2 Mbit/s, whereas DVB-H offers up to 3 Mbit/s, so it has better quality and can deliver more content. DVB-H could probably do video conferencing too, with the return path via GPRS.
Will viewers tolerate watching programs on such small screens though? Even with a PDA, compared with the huge flat screens that increasingly dominate people's living rooms, the image will necessarily still be rather tiny.
Says Chang, "It all depends on the content. Some people may be quite happy to use the time they are waiting for the bus, or going home on the train, to watch some news clips. If there are popular programs they want to watch, it could be very useful."
Looking at the economics Lin adds, "It is also possible to get extra revenue by providing programs for DVB-H, with commercials beside them, so they can't be switched off. But for 3G, operators will definitely get revenue if people want to use it, as they have to pay for the service."
The sort of content Taiwan will be providing initially, Chang says, is most likely "small clips" -- not long programs or series. Things like music videos, which of course have the 'randomness' that you don't get with an MP4 player. Also sports, and variety shows.
"We know, that in the UK, subscribers to one 3G TV service can upload their own programs and actually make money from the content they provide. And we've heard that one of the 3G telecom providers here, has this idea too."
But how will users in Taiwan feel about paying for content?
"Probably they won't like to pay!" laughs Chang, "But if there was some important event, or show... something they don't want to miss, they will pay for it. No doubt the 3G providers will bundle programs in their plans, so you can give it a try. Then, of course, when viewers get used to it, it will be hard to give up.
"But, as broadcasters, if we have a service providing much the same content, like a big soccer match, users can watch the whole match, free, whereas with 3G they would have to pay just to see a few goals. So it would seem DVB-H will naturally do better than 3G. But the 3G operators are mostly focusing on using 3G for sending data, like providing high-speed connections to surf the Internet. DVB-H is the most economical way to watch TV, whereas 3G will probably have to produce customized clips for its users."
Lin adds, "Since DVB-H can go up to 3 Mbit/s, I believe you could have up to ten channels per broadcaster, because the screen is so small. DVB-H uses MPEG-4 Part 10 H.264 encoding. There are five major broadcasters in Taiwan, so you could have up to 50 DVB-H channels here."
So, do Lin and Chang see DVB-H as likely to become a "big thing" in Taiwan? Speaking for both of them, Chang says, "Eventually, DVB-H is likely to become very popular, but right now TTV is focusing on MHP applications -- the multi-media home platform channel, or interactive TV, so we probably won't get involved with it just yet. However, all five broadcasters are applying for DVB-H frequencies. If we get approval for a frequency then we will provide a DVB-H service later this year, or early next year.
"The government is pushing digital TV," says Chang, Technical Director of TTV's Digital System Section, "but it wants to see what sort of content the broadcasters can provide before they approve more frequencies. Because if the government lets a TV station have the bandwidth, and then the station finds it can't provide useful programming content, it is pointless having the frequency. And having up to ten broadcast channels in addition to what we have now adds up to a lot more programming."
That is, in addition to the 100-plus channels you can already get on
cable...
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