Electronic Design

Cellular, Wireless Infrastructure

The wireless infrastructure market may demand the highest and most aggressive performance requirements for analog and mixed-signal devices.

Relative to mixers, some people I spoke with see a swing back and forth between established GSM and upstart WiMAX for the technology driver's seat. That's interesting, because cellular industry pundits always seem to be predicting that the demand for GSM is about to plateau. Some companies say penetration will continue to grow for the forseeable future. With carriers around 1.9 GHz, they're seeing infrastructure pushing up to 3.5 Gbits/s.

On the other hand, here comes WiMAX, with basestations proposed for carrier frequencies up to 3.5 GHz. WiBro in Korea is similar to WiMAX, but it uses specifically licensed frequencies.

Another interesting hotbed of wireless activity arises from Federal Communications Commission actions on local-loop unbundling. Regional carriers like Verizon can now lay fiber infrastructure without unbundling services. That means they can compete with cable companies. Now, the regional Bell operating companies (RBOCs) are laying fiber to the curb and to the home?not just for data services, but for video, too.

There are two ways to handle that video: digitally and via an RF overlay. RF distribution of video-on-demand over the RBOCs' fiber to the curb or to the home will be an emerging market. It requires specialized RF technology in converter detectors, mixers and modulators, amplifiers, and direct digital synthesis chips.

How about HDTV over cell phones? In the U.S., Verizon and other companies are experimenting with video clips that can be downloaded and then displayed, but that's offline download-and-play. How about those Japanese commuters we hear about (so far, it isn't clear how much has been implemented) who get real-time HDTV on their cell phones? How does that work?

My correspondents explained that there's a little-sister version of the HDTV standard that's more highly compressed, with fewer pixels for the smaller screen. In practice, a pico basestation satellite repeater would parallel the cellular telephone pico basestation, which is a repeater for terrestrial cellular basestations along the rail line.

If that's not tricky enough, the really hard part lies in getting an hour and a half of playing time from a cell-phone battery while continuously displaying a HDTV image. Higher data-converter and amplifier power efficiency would help. So would a big enough form factor to hold a larger battery array.

In the cellular basestation arena, at least two developments are resulting in fewer mixers in these basestations. There is direct conversion of a fairly sophisticated baseband signal, and high-IF, where what used to be the second and third analog mixers in a superhet design now reside in the digital domain. Expect to see something similar for WiMAX metro-area broadband access.

Still, the RF signal chain is far from totally integrated. But that's a good thing, because it allows intelligent partitioning, matching process technology to function and/or even mixing technologies on a common substrate. You will find companies using silicon germanium for active mixers and either gallium arsenide or MOS for high-performance passive mixers.

Are any technologies stalled? Alas, while basestation developers have talked about software radio for some time, and certain OEMs are producing multicarrier, multistandard radios, multistandard radios have yet to hit the market mainstream. For the most part, existing radios support multiple carriers, but only a single standard. Even so, multicarrier support pushes up specs for converter dynamic range, leading to new products for 2006.

TAGS: Components
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