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July 02 2007 at 11:35 AM
TV from the inside
GSM/3G Vision – 21 June 2007
As the number of networks supplying broadcast television grows, it would be handy to have a wider choice of handsets that allow you to watch it, albeit picture quality, screen size and resolution all offer challenges to handset designers. However, one of the biggest challenges may have nothing to do with the viewing process.Put bluntly, the low operating frequencies involved in mobile TV seemed, until recently, to leave handset manufacturers with little alternative but to create bulky handsets. Take DVB-H. As Alfonso Sanz, product manager, products and services division of antenna technology specialist Fractus, explains, DVB-H can operate over three frequency bands: VHF (around 200MHz), UHF (from 47 to 88MHz) and L band (1.4 or 1.6GHz). The 200 and 400MHz bands operate on a lower frequency than traditional cellular systems and use a broader bandwidth. Therefore a traditional antenna design approach requires a much larger antenna than is used for GSM - an antenna that is in fact larger than the current handsets available in the market.
The problem, at least until recently, was that the antenna required for low frequencies such as 200MHz was too large to fit inside a handset and therefore had to be external. A recently launched UK handset partly solved this problem by using the headphone cable as the antenna, but this rendered the device useless without the headphones.
Internal antennas must surely then be the answer but “in those cases where an internal antenna was used,” says Sanz, “the handsets were forced to be far bulkier than traditional GSM models, something subscribers will not accept.”
Mobile TV also posed major challenges to antenna designers due to the differing effects of users’ hand and body positions on device performance when viewing the TV screen (usually towards the lap) or making phone calls (usually against the head) on mobile devices. “This means that any device has to work in several modes, each of which has a significant impact on antenna - and also handset - design,” Sanz explains.
You would hardly expect a company that had not overcome these problems to be putting them in the past tense. And, sure enough, Sanz says that Fractus was the first telecoms antenna developer to announce a suite of DVB-H and ISDB-H internal mobile TV antenna solutions for all three mobile TV frequencies: VHF, UHF and 1.6GHz L-band.
All of which means that a fully customised mobile TV antenna can be discreetly housed within the handset. Job done? Not quite. There’s still the inevitable question of the combination of DVB-H and interactive (possibly HSUPA) services to further monetise mobile broadcast TV. Will this prove a challenge for antenna design?
As Sanz reminds us, the need for a low frequency for digital TV (DTV) applications is by itself an important design challenge. Adding new applications that also require a compact antenna increases the challenge. Take HSDPA as an example. “When a second antenna for Rx [receive] diversity is needed it has to be properly correlated with the main antenna, possibly affecting the position of the DTV antenna within the device - and consequently its performance,” he says. “The same design challenge would arise when combining a WiMAX application with Rx diversity and a DTV antenna within a small space. These design challenges are something happening now, not in the future,” he adds.And speaking of the future, what could a growth in consumer demand mean? The need for handsets to deal with multiple broadcast technologies perhaps?
Sanz is certain this will happen. “As there is no single standard for mobile TV being deployed around the world, antennas will be expected to integrate multiple mobile TV spectrum bands in even smaller devices, so enabling them to be applied in all form factors available today,” he says. And the end user won’t accept excuses if this doesn’t happen. “Where a few years ago subscribers would accept that a handset may work in Europe, but not in the US (or vice versa) due to the GSM/CDMA divide, today they expect ubiquitous coverage,” says Sanz. “With mobile TV, this will be no different and users will expect access regardless of the standard in the region,” he points out, and, with, presumably, opportunities as well as challenges in mind, he adds: “This will drive antenna and handset innovation in response.”
http://www.telecoms.com/itmgcontent/tcoms/events/gsmwfo/61/20017434790.html