Steven J. Crowley, P.E.
Rearden LLC filed an application for experimental license with the FCC on May 24. That caught my eye as as it’s the same company that created a splash in 2011 with its announcement of Distributed-Input-Distributed-Output (DIDO) wireless technology, said to achieve capacity 1000-times the Shannon Limit with sub-millisecond latency. The company issued a white paper authored by company president Steve Perlman and the company’s principal scientist Antonio Forenza, but it didn’t have a lot of details for an engineer. DIDO seemed to be a form of network MIMO, whereby each user is served by all base stations in its vicinity through a complex coordination process. (Various forms of network MIMO will be appearing in successive releases of 3GPP’s LTE Advanced specifications.) Aside from the white paper, there are patents that supported the notion of DIDO as network MIMO.
Network MIMO is sound in theory but there are practical concerns such as complexity of base station and user device antennas, and complex computations that need to be performed instantly based on fast feedback of channel conditions measured and relayed by the user device. With time, as technology improves, these issues become less of a concern, but 1000x today appeared far fetched, then and now, from a practical view. It seemed another of a series of announcements of dramatic improvements in radio capacity from various companies and researchers that occur a couple of times a year and are never heard from again. Sure enough, it’s been quiet on the DIDO front for two years.
I want these “revolutionary” developments to work, but I see them come and I see them go; my typical reaction is, “Elements are promising in theory, but impractical today.” Rarely, they’re real, as with the emergence of Turbo Codes in the mid-1990’s, which doubled high-speed data capacity through coding alone. When I saw the recent experimental application, I hoped Rearden had taken DIDO to a level that, if not realizing 1000x capacity improvement, would contribute to practical improvements in wireless.
After the experimental application was filed in May, I noted the fact on Twitter and also noted that the application form and exhibits had been made confidential by Rearden, so there were no specifics on which to comment. FCC staff wrote Rearden, via its attorney, on May 28 noting that the company’s request for confidentiality could not itself be made confidential, and asked that Rearden alter its filing so the request be made publicly available. In the same email, FCC staff noted that core technical details on the application form (such as power, frequency location) could not be made confidential, and said that “with your consent” the confidentiality designation Rearden applied to the form would be removed.
Rearden made the changes requested by the FCC. The application form is now available. The request for confidentiality is now available. The other accompanying exhibits are still confidential, and will likely remain so.
With these new revelations, is this a DIDO experiment? Could be, but there’s not enough detail to know for sure.
Let’s look at the request for confidentiality. Rearden requests confidentiality for Exhibit 2 – Description of Experiment, Exhibit 3 – Technical Information, and Exhibit 4 – Spectrum Use Document, saying they contain information that is “not available to the public.” Rearden also says “The services and technologies that are the subject of this application for ERS authority have not yet been fully developed but are expected to lead to material developments in markets subject to fierce competition from multiple U.S. and non-U.S. third parties who are exploring comparable services and technology.”
Looking at the application form, Rearden wants to test 100 each of four different types of experimental devices, for a total of 400. Testing is to be conducted in the San Francisco area within a 10-kilometer radius of a specified set of coordinates that plot about one kilometer southeast of the financial district. A couple days ago FCC staff sent another email to Rearden’s attorney asking for justification of the need for 400 units.
The frequency band requested is the same for all devices: 2573-2583 MHz. According to the FCC’s database, this spectrum is licensed to Clearwire, and presumably Rearden has the necessary permissions (probably covering that issue in one of its confidential exhibits).
I’m surprised by the relatively high powers being employed by all the devices. Peak transmitter power output for all of them is 20 watts. Peak effective radiated power, which depends on the type of antenna used, is one of five values: 19, 24, 49, 97, or 486 watts. From notations on the form, it appears the three highest powers are for base stations, and the two lowest powers are for devices other than base stations — exactly what they are we don’t know. (The highest-power devices are designated “fixed,” and the smallest-power devices are designated “mobile.”) Those are very high power levels for consumer mobile devices — maybe it’s some type of mobile relay, or larger gaming machine (given Perlman’s interest in online gaming) that happens to be mobile, or at least luggable. Still, 400 transmitters of 20 watts or more within a 10 kilometer radius — well, I’m not surprised the FCC asked for further explanation. For one thing, at higher power levels, compliance with the FCC’s guidelines for exposure to RF energy become more concerning. For a consumer device, I’d be looking for powers on the order one watt or less.
The emission designator, 10M0F7W, says this system uses 10 MHz of bandwidth, and transmits two or more channels containing quantized or digital information using frequency modulation, with a combination of information types (e.g., video, sound, and other data) being transmitted. There’s no one-to-one correspondence between emission designators and technologies — this one has been used for LTE, WiMAX, and digital microwave.
Lastly, I observe similarities with Google’s recent experimental application: similar frequency band (also Clearwire spectrum), San Francisco area, many devices in a small area. One notable difference is the lower power levels on many of the Google devices — one watt or less.
UPDATE 6/25/2013): Rearden has responded to the FCC’s concerns about the number of units proposed (400). It says what it means to convey is that there will be less than 50 transmitting devices, but that each transmitting device will have up to 100 antennas. That’s a remarkably high number of antennas for a multiple-user multiple-antenna communications system, and could indicate emerging very-large, or massive, MIMO technology. This use of multiple antennas is consistent with what DIDO seems to be, and it adds to the evidence that this is a DIDO experiment.