-- tl;dr Moving this to separate discussion thread --
Hi Ray, Certain people appear to want the entire UHF channel plan encoded in the > PAWS response, using very low PSD values to represent permitted leakage > into "unavailable channels". > IMHO, this is a very US/FCC-centric model. > In the ETSI model, each available channel is _explicitly_ listed, with a > low and high frequency. "Unavailable channels" are omitted, and there's no > concept of needing to describe the channel plan. Devices just do what > they're told, and adjacent channel leakage into otherwise unusable channels > is controlled by device approval regulations. I humbly suggest a few alternate viewpoints: a) AFAIK, in every regulatory domain, multiple device regulations are simultaneously in effect at all times. Just because a device is following TV WS rules, does not excuse it from complying with other rules like EMI leakage or electrical safety testing. Just because a set of frequencies is not explicitly mentioned in one section of the law does not mean that those frequencies are unregulated. Every piece of spectrum is controlled by at least one law. There is no such thing as completely unregulated spectrum. b) In the case of the ETSI model, the emission limits on channel 38 can be derived using the adjacent channel leakage ratios for each device class. From a technical standpoint, Ofcom must assume some kind of power limit (interference threshold) on channel 38 in order to compute the white space power limits on channels 37 and 39. The power limit on channel 38 is the same one that can (and should) be communicated to the device. Not having looked at Ofcom's data set yet, I think it's a little premature to say that they will be silent or explicitly omit data for channel 38. c) From a future-proofing perspective, I think it's important to communicate these "band edge" requirements. One of the great features of a spectrum database is the ability to modify the rules over time. Future changes to the white space rules might involve shifts in the frequency ranges, changes to power levels, or perhaps changes to the band edge roll off. The key is that the DB is responsible for protecting the primary spectrum users, and by communicating the "left-over" spectrum envelope to white space devices, you give them the chance to opportunistically use that spectrum. The way in which the white space spectrum is specified can determine how effectively a WSD can search for opportunities within that envelope. I've put together some crude hypothetical examples in the following illustrations: Case 1: Old profile has "square" channel edge restrictions. WSD needs to narrow its in-band emissions to avoid causing interference on the adjacent channel. [image: Inline image 1] Case 2: New rules define a more realistic band edge rolloff, but also lowers the emission limits on the left-most channel. WSD peak emission power remains the same, and its in-band emissions can be moved closer to the channel edge because the new rules allow it. [image: Inline image 2] Case 3: Consider what white space devices must do when they try to find optimal channels to transmit on. Specifying the channel edge emission masks actually gives the device more information to work with. The band edges can and should be factored into the search for the optimum spectral fit of a signal. A legacy device does not know how the out-of-band rules might change in the future, but with a fully defined profile, the device can still do the right thing at the band edges even when the rules change. [image: Inline image 3] Best regards, Andy Lee | Google Inc. | [email protected] | 408-230-0522
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