FCC ruling expected

Excellent business journalist Dana Blankenhorn says a ruling is expected from the FCC real soon now that will clarify MBOA’s legal status. The main issues is that MBOA uses frequency hopping to reduce emissions in each frequency band by lower duty cycle. The FCC has a hard time measuring frequency hoppers because they have clunky equipment, so they request FH be turned off for emission measurement purposes. This is trouble for MBOA because they only do FH in the first place to please the FCC. So it goes ’round and ’round.

The MBOA system is better than the Freescale DS-UWB because it can be tailored to operate in different regulatory domains where various services have to be avoided by the UWB transmitter – it divides spectrum up into chunks that can be enabled or disabled. DS-UWB is all-or-nothing, a simper design but illegal outside the US.

If the FCC requires MBOA to turn off FH and flunks them on account of it, we can look forward to a world where there is one UWB standard for the US and another for the rest of the world.

That would not be cool, of course.

16 thoughts on “FCC ruling expected”

  1. Actually, DS isn’t “all or nothing.” DS overlay systems go back a long, long time. Freescale’s solution is not an overlay, but it could easily be made one.

    There’s really only a single overriding argument in favor of MBOA: it gives a platform that presumably can be cheap because it’s based on a modulation widely deployed in 802.11, and may be widely deployed in WiMAX.

    But otherwise, all other things being equal, they’re really a wash.

  2. No, not really. The DS system overlays a continuous chunk of bandwidth, same chunk all the time. The MBOA system jumps around and easily be programmed regarding frequencies to use and not to use. In this sense DS is an “all or nothing” overlay.

    In most countries, Japan being a good example, there are services such as radio astronomy that UWB is not allowed to overlay. So a UWB system, if it’s to be used worldwide, needs to be tailorable to local regulations. MBOA is, and DS-UWB (they used to call it DS-CDMA) isn’t.

    Is OFDM really cheaper than CDMA? Not in any meaningful way; these systems are built out of ASICs so the only cost is the number of gates to implement the algorithms. People don’t use a “universal OFDM chip” to implement DSL, .11a, and OFDM so popularity isn’t really an issue.

  3. No Richard, you’re wrong. There’s no reason to design DS systems that way. For example, in the 1990s I worked on a 15 MHz DS system that was an overlay for the AMPS band. AMPS frequencies were adaptively notch filtered.

    It is indeed possible to do this in regulatory environments; you merely have to design filters to meet the requirements they would have to meet to meet the regulatory environment.

    There’s actually other ways to do it too (such as manipulating the chip shape), but I suspect that explaining that to you won’t stop you from denying the obvious.

    And, as Srini tells me, the FCC’s equipem
    nt isn’t the matter either; its the band occupancy.

  4. It’s possible to do lots of things, but you aren’t describing DS-UWB as it is, and you don’t fully appreciate why MBOA was designed the way it was. It has to spread over a certain bandwidth to meet FCC requirements, and they chose to do that with FH in order to reduce transmit power and increase signal acquisition accuracy. This design also gives MBOA the intrinsic capability for adaptation under MAC control, something the real DS-UWB system doesn’t provide. It’s a pulse radio system that occupies an enormously wide band all the time.

    Srini’s take in the FCC measurement system is at best idiosyncratic. He says that they should turn FH off in order to see the effect of multiple simultaneous transmitters. Excuse me, but we measure all other systems one at a time, so what’s good for the goose is good for the gander.

    Folks with a vested interest in WiFi dominating the home aren’t the most credible sources of design critiques for UWB, or of MACs for that matter.

  5. Actually, after I commented to Srini about your post, he remarked that Freescale did indeed have a chip-shaping type of system in development.

    And Srini’s just telling you how the FCC does its measurements and why they might be objected to.

    I should add that we, personally, do not have a “vested interest” in Wi-Fi designing the home, but collectively we have well over 30 years’ experience in the desgin of spread-spectrum and related systems.

    A guy with no real experience in signal processing, communication theory, coding theory, channel characterization, how to interpret and create a radio link budget, the interpretation of FCC regulations, etc. is not really a credible source at all.

    Stick to the MAC, and higher layers.

  6. Mummie, you’re a WiFi Alliance activist and Srini’s the editor of 802.11e. How can you guys claim to have no vested interest in 802.11 when you’ve collectively invested ten years in it?

    Not that it’s relevant, but I’ll gladly stack my knowledge and experience with networks (including the PHY) and government regulations against yours any day, thank you very much.

    When the arguments from authority come out you know who’s losing the argument.

  7. Activist? Hardly. Just ust doing my job. It’s actually much more accurate to say I have a “vested interest” in the projection theorem, in Bellman’s algorithm, detection and estimation theory and adaptive systems.

    And from the standpoint of my job, the particular flavor-Wi-Fi or UWB or PLC etc. doesn’t really matter; what matters is connectivity

    To put it another way, one of the first things my father designed many decades ago is a bridge in India. Did he have a “vested interest” in bridges in India that kept him from advocating using other bridges? No. He had a “vested interest” in the structural properties and applications of steel.

    If you don’t understand that very very simple point: that we don’t care that much about any particular realization of technology, but it’s impact on the market and user, well, what were you saying about your experience?

  8. John, you’re a committee chair in the WiFi Alliance, or were very recently. Who do you think you’re bullshitting?

  9. My being a committee chair in Wi-Fi is just part of my job, and as such, I am there to carry out the policies of my employer. I also was involved in efforts to evaluate UWB technologies as well, for the same employer.

    Long before you were involved.

    I think you’re losing it…

  10. No, I’m not the one who’s been touting his knowledge of such irrelevancies as coding theory in a discussion of UWB and interference in order to lend gravity to his points – I just stick to the facts as they are today. That’s not as they were three years ago when you last looked at UWB, or next year when the DS-UWB system is re-designed for foreign compliance.

    The principal fact under discussion is this: MBOA relies on frequency hopping to disperse energy across a wide frequency band in order not to interfere with licensed spectrum users. Turning off the frequency hopping alters the system in a fundamental way from the standpoint of interference. Is it right for the FCC to do this, or does it so alter the system under test that the test results are rendered meaningless? I say the FCC is wrong. What do you say (except to tout your education, which I stipulate is impressive)?

  11. Well, Richard the original issue was my point that you mischaracterized DS systems (of which coding theory plays a part in the overall design of the radio, BTW). Neither was any red herrings about Wi-Fi. This started as a point on engineering.

    The FCC needs to make sure that the system as used will not interfere with incumbents in a given band. If any system is jamming the incumbent 1/3 the time, it is indeed a problem.

    Turning off the frequency hopping and going 5dB down in power in this case is cheating actually, since the real effect is jamming the channel 5dB higher when it is on.

  12. Coding theory doesn’t have anything to do with the FCC’s interference measurements, does it? And “jamming” is a function of power, bandwidth, and time.

    UWB systems work by sending out short pulses at low power over wide chunks of licensed spectrum. The theory is that these pulses look like white noise to the incumbents. Altering the signal strength, the duration, or the frequency of these pulses significantly alters the behavior of the system as a potential source of interference.

    The FCC should test the system in its normal operating mode.

    DS-UWB has additional problems independent of interference with licensed incumbents, such as CCA. It’s not even clear that this system will work in an acceptable way in a significant number of applications, so the consensus of the highly-qualified Ph. D.’s I’ve consulted (including MIT and Cal Tech guys) is that Motorola/Freescale has significantly oversold it.

    We’ll see.

  13. Altering a signal’s strength does nothing to affect the shape of its power spectral density.

    I’ll ignore your argument from authority (I studied under IEEE fellows myself.) But I will say that I was one of the first people to opine that the DS folks oversold their system since its ability to manage interference in nearby independent piconets is laughably optimistic (repeat after me: multipath destroys orthogonality). I don’t know if that’s what you mean by “working for all applications,” but in a single independent piconet with no other interferers, there’s nothing that prevents theat physical layer from operating with multiple applications.

    I should also point out that there is a relatively trivial way out of hell for the MBOA guys: all they have to do, really, is get the FCC to write in some channel sensing rules akin to those for part of the UNII band. But that will mean that they will, in some environments take a serious capacity hit, but that’s the price you pay for operating as a user in licensed band.

  14. Altering a signal’s strength does nothing to affect the shape of its power spectral density.

    No, but it does affect its potential to interfere with distant services, doesn’t it? So we test the system as it is.

    Your other remarks are non-controversial, except for the one issue with single piconet: if the system can’t provide CCA, it obviously can’t do CSMA because the piconet interferes with itself.

    DS-UWB is a pretty sad system.

  15. That’s not a PHY problem, that’s a MAC problem, the MBOA guys were working on that… good luck to ’em… given the folks involved, they’ll need good luck.

    But there’s not technical obstacles there, really.

  16. CCA is a more serious problem for DS-UWB than for MBOA, and it’s a MAC problem that has to be solved in the PHY.

    The 15.3a MAC is largely a missing-CCA-workaround, and you know what a pile of crap it is.

Comments are closed.