WTF is... RF-MEMS?
Apparently, a way to make smartphones much, much better phones
Feature Smartphones nowadays come with big screens, megapixel-packed cameras and, thanks to apps, many, many more features than anyone could have dreamed of in the early days of mobile telephony. It has even reached the stage where making telephone calls is just one small part of a modern phone. And yet the need to support all the radio technologies punters expect to be able to use, for voice and for data, ensures that wireless communications is still the hardest part of a phone’s design to get right.
Just ask the guys who worked on the iPhone 4...
Steve Jobs explains Apple's grip-of-death iPhone 4 antenna design
That was in 2010. Today, more than two years later, your typical smartphone is even more complex, wirelessly speaking. A 2012 handset might be expected to feature Wi-Fi in two different bands: 2.4GHz and 5GHz. Bluetooth too, in the 2.4GHz band. Then there’s 4G LTE for fast data communications and 3G for voice - because 4G can’t yet do voice properly - and for data in places where 4G hasn’t been rolled out yet. Just in case the user roams into a region without 3G either, phones still have to support 2G. All this cellular goodness has to work across a range of frequency bands to support different carriers in different countries.
Oh, and don’t forget there’s more wireless goodness coming. Devices are soon going to have to start supporting 60GHz short-range, high-speed data transfer communications if they’re to continue offering the full 802.11 standard. WiGig - aka Wireless Gigabit - builds on the agreed 802.11ad 60GHz specification and it’s coming in 2013-2014, trailing new pick-up specifications in its wake.
To get the promised ever higher data transfer rates, devices need to stick to these newer radio specifications very closely. Old, broad tolerances which might have been acceptable in the GSM and GPRS days will no longer do. That means more effort needs to be put in to get each antenna turned correctly from the off.
To make it all work, today’s smartphones need multiple, pre-tuned antennae and a host of different chips to manage the signals for each of these technologies. And they all have to fit within the phone’s casing. No one, after all, wants to go back to extendible external aerials.
Were punters happy with ever-fatter phones, that would be much less of an engineering problem than it is, but they’re not - they want thin, pocket-friendly devices.
The solution might seem obvious: build in a single, universal radio able to hop across all those radio technologies and frequencies at will. It’s an answer that’s easy to state, rather harder to realise.
Back in September 2011, Samsung released a Windows Phone smartphone, the Focus Flash, which featured a little-known first: it contained a radio frequency micro-electromechanical system (RF-MEMS). This tiny chip, developed by WiSpry, a company based in Irvine, California, was capable of physically changing its impedance under the influence of a software. The upshot: it could be used to dynamically tune the Focus Flash’s antenna to meet the needs of some if not all of the radio technologies the phone uses.
WiSpry has been working on RF-MEMS chips for more than ten years. Indeed, MEMS makers have been shipping these kinds of chips since the middle of the last decade. Getting them to work with mobile phones has long been a goal, but it’s proved hard to attain. While phones were chunky and could be stuffed with all the antennae they needed, there wasn’t much need to implement RF-MEMS in handsets. There were fewer radio technologies to support too.
Next page: Antennagate
COMMENTS
How's that software-defined kool-aid?
You may as well say, ignore BluRay technology, because CPUs are getting more cores.
SDR *decodes* the signal. Antennae *receive* the signal. SDR won't magically improve the signal-to-noise ratio at your analog stage. SDR and RF-MEMS are complementary technologies, not competing technologies.
As for the rest of your software-defined kool-aid:
"SDR seems to have so many advantages of this technology, for instance no having to constantly "switch" between frequencies but just "hear" them all, all the time, that I can't see a real market for this."
SDRs heterodyne the frequencies from "very very high" down to "low enough to sample". The ADC bandwidth allowing you to not heterodyne isn't *quite* there for 2.4GHz and above - I'm not aware of a consumer-grade 5Gsps ADC. And sampling the entire signal is very wasteful of power, if you don't need to.
"Not only that, they can transmit too"
This all depends on the analog stage of the SDR. Most SDRs don't transmit, because you need a license for most bands, and it is *extremely* dangerous to provide a transmitting SDR if there's *any* danger of it accidentally transmitting on the wrong band. Dangerous as in putting lives at risk. Fully user-configurable software-defined radio transmitters are never going to be available to consumers, sorry.
"Ignore this tech. Push your money into SDR."
Total non-sequiteur. I recommend you study RF analog stage design, Fourier's theorem, heterodyne theory, and look at the kinds of ADCs that are cheaply available, just to at least get a *flavour* for this subject, before writing off an antenna tuning technology on the basis that it's not your favourite signal decoding technology.
> Surely RF-MEMS is just a stop-gap, then, until software-defined radio (SDR) takes over. SDR is basically just connecting a "good enough" antenna over a range of frequencies
I don't think they are the same thing; RF-MEMS is a software defined antenna rather than a software defined radio. You would want to hook the two together though....
I do SDR for a living.
I do SDR for a living, and you are wrong. There are 3 things that prevent your idea from working:
1) Not enough bits on the converters. To have an SDR in which the antenna dumps into the converters, you need very fast converters - to cover all the bands a phone might need you'd be looking at gigasamples per second - hundreds of gigasamples per second to do 60GHz. The best gigasample converters are around 12 bits. The dynamic range just isn't there - a strong signal in the FM band will swamp the converter and prevent it from hearing that weak signal in the cellular band. Yes, you get some processing gain as you band-limit the signal in the digital domain, but if the desired signal is too small, you still won't be able to resolve it.
2) not enough processing power. Even if you ignore the above, it takes a lot of processing power to handle a gigasample/second signal. Your phone will last just long enough to open the socket before draining the battery.
3) Noise. Sorry, we live at about 280K - and the noise floor is such that a wideband converter will see so much thermal energy that it will be swamped no matter what. Remember point 1? You don't even need a strong FM signal in the area, just the thermal noise from the phone will be enough. Unless you want your phone's 500 kg batter (remember point 2?) to be even heavier to run the cryopumps to keep your phone's front end at 2K.
Even the best SDR on the market has a few analog IF stages to bring the signal down in frequency to something more reasonable, and to band limit it to bring the noise floor down, and to decimate the sample rate to something that can be processed reasonably.
tl;dr: - you still need to have a tunable antenna, SDR isn't a panacea.
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