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[Ham-80211] OT??? High power 2.4 GHz rules change

Carl R. Stevenson wk3c at wk3c.com
Sun May 21 17:53:32 UTC 2006


 

> -----Original Message-----
> From: ham-80211-bounces at lists.tapr.org 
> [mailto:ham-80211-bounces at lists.tapr.org] On Behalf Of hal
> Sent: Sunday, May 21, 2006 12:15 AM
> To: TAPR Mailing List for Ham Radio Use of 802.11
> Subject: Re: [Ham-80211] OT??? High power 2.4 GHz rules change
> 
> Tim Gorman wrot
> > Those multiple stations have to be able to communicate or 
> they are worthless. 
> > The higher power they run the more they interfere with each other. 
> > It's why the cell phone people don't just increase their cell site 
> > power in order to increase capacity (i.e. they can reach further 
> > distances and cover more people). They actually lower the 
> cell site power and put more cell sites in.
> >
> >
> >   
> You seem have a pretty strong opinion on high power spread 
> spectrum so I am amazed you have not heard of the overlay 
> concept that was the original reason the FCC authorized Part 
> 97 use of spread spectrum in the first place. If I choose to 
> experiment with a multipoint frequency hopping system on 
> 2.4Ghz and pick the power, dwell time and channel spread, 
> modulation type, etc .correctly there will be little 
> interference to other fixed carriers in minimal.

However, you must be permitted to use appropriate spreading codes ...


> The analogy 
> with cell phones is bogus and led to the introduction of APC 
> to start with..  I spoke up against inclusion of APC when it 
> was proposed but it was politics, not experimental evidence 
> or experience with Part 97 SS systems that championed into the rules.

The analogy with CDMA cellphone technology is applicable ... There, the
spreading codes are chosen to have low cross-correlation, and tight power
control is necessary to allow CDMA reuse - if the power control is not good,
the system will fall apart pretty fast.

> There was no experimental experience, then or now, that this 
> feature in any way promotes experimentation, enhances 
> innovation or is required to safeguards shared users.

I don't think anyone ever stated that APC "promotes experimentation" or
"enhances innovation," however it IS a good idea to promote good sharing and
efficient use of the spectrum.  One QRO system (say 100W into one of the 15
dBi slotted waveguide omnidirectional antennas that I've seen plans for)
will blanked a wide area with enough signal to severely disrupt dozens,
perhaps hundreds, of WLANs that could otherwise share the spectrum quite
effectively.

I see the wide area (omni, point to multipoint) 802.11x use that many hams
tend to envision, based on the FM repeater paradigm, as being extremely
inefficient and a misuse of a technology that was never intended to be used
in that way.

> The authorized
> code sequences we received after a lot of behind the scenes 
> back and forth are so limited as to be pathetic.

Agreed ...

> The FCC essentially shutdown all planned experimentation with 
> advanced code sequences, one of the most promising and 
> fruitful areas of spread spectrum research.  A few weeks 
> after this debacle they authorized practically  any sequence for 
> commercial users.

The commercial (Part 15) users aren't allowed to run 100W output with no
limit on antenna gain ...

> Hams themselves killed  Part 97 spread 
> spectrum  off 
> 2meters because of imagined fears of interference. After 
> reading the reply comments the Commission imagined all kind 
> of complaints from the repeater operators who where 
> themselves unaware of spread spectrum testing right on top of 
> their allocation when it actually happened.

Agreed ... Given that the repeater bands are grossly underutilized (too many
repeaters that aren't used all that much, essentially "warehousing" channel
pairs) an adaptive FH overlay, done properly, would be very feasible.
 
>  There continues to be a profound misunderstanding within 
> amateur circles on spread spectrum.  Correctly chosen system 
> parameters will produce a spread spectrum system that will be 
> difficult to even detect without specialized equipment.  As 
> an argument against high power 802.11 that uses spread 
> spectrum (as opposed to OFDM or other modulation techniques) 
> it is full of holes.

OFDM (as in 802.11a/g) has essentially no greater interference potential to
"conventional" uses than does an "old-fashioned" DSSS system using the
stupid 11 bit Barker codes that they used ... The spectrum mask and power
spectral density are virtually identical.

> All this is argued even when it is a  known fact that there 
> are very few such experimental spread spectrum amateur 
> systems anywhere in the US.  APC does nothing to safeguard 
> 802.11 users who have valid concerns over badly engineered 
> high powered 802.11 systems.  Maybe thats where the APC  
> belongs, not as part of the spread spectrum rules.
>  In short, APC is a bad idea for Part 97 spread spectrum,  it 
> adds complexity without purpose, it stifles innovation and 
> doesn't protect anyone in an already overly regulated Amateur 
> service.

APC (802.11h, which rolls into the base 802.11 standard) isn't an onerous
burden as some would assert ... In fact, with most amateur SS using off the
shelf or (slightly) modified 802.11x equipment, where's the rub???  For
those who want to "roll their own from scratch," I would agree that the
current rule ("limit power to that necessary to produce a 23 dB Eb/No at the
intended receiver") is awkward and could be improved, but I do *not* favor
the removal of an APC requirement.  APC is good engineering practice.  Too
many hams pay NO attention to the "use the minimum power necessary" rule.
Any evening, you can tune the HF bands and hear any number of people running
legal limit (or more) on 80m/40m/20m to talk to some guy across town ... Bad
amateur practice, but, unfortunately it's quite prevalent and in many ways
part of the mindset of (far too) many in our ranks.
  
73,
Carl - wk3c





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