In my last post, I looked at how privately-held Artemis has created a system which they claim can unlock immense amounts of wireless bandwidth. They use DIDO techniques, and a new access point which they call a pCell to transmit a single signal which can be decoded differently by each device in the cell’s radius.
Heady stuff, if it works. And they certainly have a solid demo video. But I still have a lot of questions as to how they achieve this.
I will fully admit that most of the technical solution will lay beyond my meager technical abilities (said the Chinese History major). Still, I wanted to learn more. And having done more than my fair share of company research I set out to try to understand pCell.
Which is where I start to run into trouble. The founder of Artemis is a serial entrepreneur. He has a track record of successful companies he has started and sold, or continues to incubate in his own portfolio. More than anything else, I think this gives Artemis a lot of credibility. Benefit of the doubt goes to them. However, the drawback of this is that he has mastered the art of the pitch. The company has done some very good marketing, but it is almost too slick. I get the sense that the team has been burned before by the press and are managing their image very carefully.
As a result, it turns out that there is very little technical detail available on Artemis or pCell. Their website looks very nice, but has very little in the way of hard data. There is a link to that demo video, and links to all the positive press coverage, but no technical links. A Google search for “pCell Whitepaper” does yield a download from the company. That whitepaper was the basis of my last post, and it is helpful, but is not deeply technical.
There are many reasons why the company does not want to share more information. Most likely, they are still filing or just preparing the key patents. There is also some smart marketing at work. They start with the consumer appeal, the big picture ideas. If they started with the technical details they would likely be swamped quickly by a sea of technical quibbles with their ideas, bogging us down in minutiae. Artemis has the potential to be very disruptive, and those threatened have armies of engineers and marketers who could quickly clog the debate.
That being said, Artemis is making some big claims. They are picking several fights here, and at some point soon they will have to release more data.
I imagine that there are some limitations to this system. They do not appear to be limits of scaling, or device capacity. Last post I wondered how the system handles cell to cell hand off. The cellular standards spend a lot of resources handling the administrative side of communications (as opposed to the message itself). Those are serious problems, and I am curious how pCell handles them. And that is just the start of my list of questions.
Another big, related question for me is how mobile is this system. Meaning, how fast can I be travelling with my device? My guess is that pCell depends a lot on knowing the exact position of the receiving device. If I am in a car going 65 mph that may pose a problem. But it’s just a guess.
I did try to one other approach for understanding the system. Their CTO is Antonio Forenza, and a Google Scholar search yielded several interesting papers he published through the IEEE.
Below are some links to a few that looked relevant, the first three seem to be the basic science, followed by two that look like simplifications to the key algorithms.
Benefit of pattern diversity via two-element array of circular patch antennas in indoor clustered MIMO channels
Adaptive MIMO Transmission for Exploiting the Capacity of Spatially Correlated Channels
Adaptive MIMO transmission scheme: exploiting the spatial selectivity of wireless channels
A low complexity algorithm to simulate the spatial covariance matrix for clustered MIMO channel models
Multiplexing/Beamforming Switching for Coded MIMO in Spatially Correlated Channels Based on Closed-Form BER Approximations
Looking at these, I would speculate that pCell takes advantage of the fact that radio waves change as they travel through space. The signal a device receives at point A is going to look different at Point B, even if the two points are only a few centimeters apart. So the trick is to transmit a signal from the pCell access point which is designed to alter slightly from Point A to Point B, and the receiving device can make use of that difference to receive a different message depending on location, or multiple devices get different messages from the same transmission. If you look at the abstracts from these papers (and that is all I had access to) there is a lot of discussion about correlation of ‘channels’ (radio signals) differing spatial conditions, with the key word being ‘exploiting’ those affects. Then there is the paper on a low complexity algorithm which speaks to the fact that this is some complex math and you need simplification to make sure the cloud servers do not get overburdened.
As I said at the outset, Artemis deserves the benefit of the doubt, but they still have some ways to go to prove credibility, let alone commercialization.
Long ago— before I’d had any calculus — I was a broadcast engineer, operating/maintaining a commercial FM station. But I then went into math, econ & finance, so I’m not THAT far ahead of your Chinese History skills. At least you should know a thing or two about convoluted situations.
It appears that this takes MIMO concepts to a much more advanced level in at least two ways:
First, MIMO exploits the “interference” of multiple antennas’ signals to form a tight beam — both of radiated power and sensitivity to inbound signals. The abstracts show aiming of specific information, and/or time-switching which way beams go. Wikipedia’s “beamforming” describes it and has links to images of it. MIMO goes to “adaptive” beamforming by changing the relative timing of signals to the different antennas, to steer the signal like a radar array would, and more.
Second, pCell appears to exploit constructive interference from multiple sources. Like beamforming, this might create a small volumes where the signals reinforce to be much stronger than outside the “personal cell.” Imagine spotlights from three different angles, except the lights reinforce each other at their intersection.
Third, tracking multiple devices accurately enough that you can use these tiny cells, especially if they’re moving, and then deciding how best to divvy up the signals among different MIMO and other approaches appears to be a Hard Problem. It appears that rather than solving a bunch of simultaneous PDEs, one paper has a matrix simplification. Solving matrices challenges people but it’s a commonplace in science and other computations so forcing it into that bucket means that especially thanks to web-based solvers, individuals can be tracked without losing them.
Again, far-from-expert guesswork combined with chintziness of not wanting to blow $30 per paper.
And thanks for pulling together what you could. Very interesting.
MIMO has become a fairly mainstream technology, making an appearance in 801.11n and various flavors of LTE/Wimax etc, so it’s not really new. There are new variants of this, including CoMP and Massive MIMO, which are reasonably active research topics.
I’ve spend a couple of hours digging through the White paper to figure out what’s going on, and it’s hard, because there’s not much info. There’s some more discussion here
I tend towards the “Extraordinary Claims require Extraordinary Evidence” which is currently impossible with the information released.