Hi Ben, And that means NO intentional radiation in the channel.
If you are reading this as "transmitted emissions in band should be lower > than -33dBm" then, no, this is not the same as "no emissions" per FCC > rules. If one were to intentionally transmit at -33dBm where no intentional > emissions are allowed, that would not be the same as "no" under the rules. There is certainly no intention to encourage any malicious behavior. In general, we expect devices to be trying to do the right thing and just need some information to understand where the boundaries are. These boundaries include both intentional and unintentional emissions. Various modulation types have known spectral profiles, including both in-band and out-of-band emissions. Knowing where the "shelf" is on the adjacent channel makes it possible to match that with the "skirt" of the intended modulation pattern. The "skirt" is not part of the intended emission, but is important in trying to avoid causing interference on adjacent channels. A crude example of this is shown in the following image: [image: Inline image 1] Best regards, Andy Lee | Google Inc. | [email protected] | 408-230-0522 On Fri, Sep 20, 2013 at 3:07 AM, Benjamin A. Rolfe <[email protected]>wrote: > > On 9/19/2013 9:09 AM, Andy Lee wrote: > > The math bears that out, but nonetheless OFCOM are still effectively >> proposing that *no* in-block transmissions are allowed in that channel. > > > Same is true for the FCC. The FCC also assumes that "off" channels are > not used by WSDs. > > And that means NO intentional radiation in the channel. > > > Specifying a low power level like -33 dBm is effectively the same thing > as specifying no in-band emissions there. > > > If you are reading this as "transmitted emissions in band should be lower > than -33dBm" then, no, this is not the same as "no emissions" per FCC > rules. If one were to intentionally transmit at -33dBm where no intentional > emissions are allowed, that would not be the same as "no" under the rules. > > > > Even if someone did try to put an in-band emission there (regardless of > how impractical that actually is), it would be too low to cause > interference to anyone and no harm has been done to the "RF environment". > > Should be a little careful here for a couple reasons. I've designed and > shipped communication systems that operate quite well with transmit power > levels intentionally below -33dBm and do very useful things. It's pretty > easy to design a receive with sensitivity better than -96dBm, so an > intentional radiator at -33dBm near by will be noticed - at 900 MHz your > 10dB above sensitivity at 10m and at 54MHz you'd be 10 dB above sensitivity > at 100m, possibly. And when it comes to protecting their spectrum, people > always use the best propagation model to calculate interfence impact on > them :-). I've probably misunderstood something badly, but -33dBm is > certainly enough power to be noticed. > > I have tried the "too low to be noticed" argument a few times in the past > in regulatory discussions, and incumbent and/or protected users usually set > the threshold closer to -120dBm and usually argue that even at really low > TX power, the "aggregate impact" of multiple devices in the "RF > Environment" is an unacceptable impact. We had trouble with this argument > when the intentional radiator TX limit was below the maximum unintentional > emission limits for most non-transmitting devices (-41.3dBm). > > So it would be fairly important to ensure a device does not interpret > -33dBm as it's ok to use that channel so long as it's TX power is below > -33dBm. > > I may be off base here because of how y'all see the DB providing and what > I am expecting to support future needs. "protected users" includes more > than TV stations in the US. > > Not sure that helps, but hope so. > > > > The advantage of having an "well behaved" spectrum profile (contiguous > and without special values like -inf) is that the channel selection > algorithm on the WSDs becomes much simpler and logical. There's no need to > have lots of special boundary condition checks and code paths that only get > triggered under special circumstances. I'd like to avoid ambiguous > interpretations on the device side as much as possible. > > Certainly ambiguous interpretations on the device side are a bad thing. > > Some apps are aggregating multiple TV channels to get a logical channel > that that can carry a 'wide' data pipe. Other uses can fit many useful > channels in one TV channel. In 802.15.4m we divide the TV channel up into > multiple physical channels carrying low data rate signals. Right now we > assume a peak power level for the TV channel, and we get that value with > the start frequency and width (or end frequency) from the database. > However, I've heard it proposed to the FCC that we may get different power > limits different parts of the TV channel, changing over time, as a > protection mechanism for deal with narrow band protected users while > allowing effective use of the rest of the TV channel. For what we do, this > is a good thing - our physical channel may be less than 200kHz wide. There > are a LOT of applications in IoT that need < 200kHz channels, and > blocking an entire TV channel to protect a wireless microphone using < > 200kHz of it means there are 28 other usable channels not being used - not > efficient use of the spectrum. > > Hope this helps. > > -Ben > > > > Andy Lee | Google Inc. | [email protected] | 408-230-0522 > > > On Thu, Sep 19, 2013 at 8:30 AM, Ray Bellis <[email protected]>wrote: > >> >> On 19 Sep 2013, at 16:21, Andy Lee <[email protected]> >> wrote: >> >> > This actually shows that Ofcom has picked a power threshold on channel >> 38 of -33 dBm. If you look at the ACLR numbers for class 3, 4, and 5 >> devices, you'll see they are 10 dB apart from each other and that they all >> work out to be -33 dBm on channel 38. >> > >> > The reason there are no limits for class 1 and 2 devices is because the >> in-band power on channels 37 and 39 cannot exceed +36 dBm/8MHz, and >> therefore the power on channel 38 will naturally be less than -33 dBm. >> >> The math bears that out, but nonetheless OFCOM are still effectively >> proposing that *no* in-block transmissions are allowed in that channel. >> >> Per OFCOM / ETSI device interface requirements it would be incorrect for >> us to actually send that value of -33 dBm to a device. >> >> Ray >> >> >> > > > _______________________________________________ > paws mailing [email protected]https://www.ietf.org/mailman/listinfo/paws > > > > _______________________________________________ > paws mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/paws > >
<<Intentional vs Unintentional signal.png>>
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