Jason: Part 15 contains no requirement that minimum power be used. It will after the final rules for the white spaces are codified — and that will be ONLY for the white spaces. However, there is an inherent problem in it: to determine the minimum power required to communicate, you have to turn the power down regularly so as to cause communications to fail. Broadband providers’ equipment cannot do this; it needs to work perfectly, 24×7. Another reason why the release of the white spaces as unlicensed is a horrible idea.

On a shared channel, only one frame can be successfully
transmitted at a time, so the length of time my neighbors occupy the
channel directly affects my ability to use the channel.

Besides being not true (c.f. any non-TDMA system like CDMA or FDMA)
the implicit model being discussed is non-cooperating users. That is,
other users of the channel are external interferers.

You don’t
need Shannon’s Law to understand that, it’s simple arithmetic.

Like I said in the previous post this has nothing to do with Shannon’s
law (the premise used is the rate-robustness tradeoff which I do not
dispute).

All else being equal the rate at which other users transmit has no impact on the performance on a given user’s communication.

On a shared channel, only one frame can be successfully transmitted at a time, so the length of time my neighbors occupy the channel directly affects my ability to use the channel. You don’t need Shannon’s Law to understand that, it’s simple arithmetic.

The corollary of Shannon’s Law is that lower data rates require less bandwidth, Jason. Work the problem of low signaling rates in a shared channel and I think you’ll see Brett’s point. If it’s not immediately obvious, consider that many of our popular wireless systems use redundant coding to increase robustness, simply adding or subtracting redundancy at constant modulation.

I understand perfectly well that you can trade robustness for rate. I
was disputing that this is a consequence of the channel capacity
theorem. My opinion is that working with capacity and interference is
not informative: rate and BER are meaningful. But this unimportant
in order to make the following point:

All else being equal the rate at which other users transmit has no
impact on the performance on a given user’s communication. The
rate-race-to-the-bottom assertion is not valid.

Jason, you should read the Part 15 regulations. They absolutely do not say that a device should transmit with no more power than necessary

The whitespaces order says:

All devices must include adaptable power control so
that they use the minimum power necessary to accomplish communications.