Mr Matt
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Eustis, FL
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| The Luddites are coming, the Luddites are coming!  The NAB is concerned by a non problem. When the original NTSC standards were created in the 1940's, Vacuum Tubes were the norm and bandpass filters were so primitive that a one full channel guard band was required between VHF channels and a six channel guard band was required between UHF channels. Today's sharp cutoff filter technology will allow low power white space devices to operate within unused channels without causing interference. With proper shaping of the white space devices broadcast spectrum, higher power devices could be used without causing interference and that is what I believe has caused the NAB concern. Extensive field testing has shown that the use of a vacant channel used as a guard band would not degrade reception of adjacent active Television Channels. I would like to see the NAB to prove that the use of vacant channels will cause interference. |
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| The problem is what is a vacant channel.
From the ground level, signals are below -120dbm, well in the noise.
Put a CM4228 antenna up on my roof, clear the trees and the NYC DTV signals come in at more than -100dbm, locked and stable.
But my neighbor's WSD wouldn't know, since it would not detect below the -114dBm threshold, and fire away. Add a few more of these and it would mean I'd have to give up any hope of getting TV OTA reception.
Furthermore, some guy will post in the forums "hey unlock your broadband modem" and someone will figure out how to disable busy detection. Then all hell breaks loose and these guys will be transmitting on used channels.
RadioDoc said we should limit it to a few channels. I tend to agree. Put it on low VHF where almost no one is broadcasting. Or maybe share it with land mobile on 14-20. But don't let it loose from 2-51. That's asking for trouble. |
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| said by fifty nine:The problem is what is a vacant channel. Exactly. A receiver can't notify its reception of a channel to whitespace devices in the area. And unless the whitespace device has exactly the same antenna as a potential interference victim, oriented the same way, and has the same receiver sensitivity, it can never identify a vacant channel with 100% certainty. Filtering is useless if the interference is co-channel.
While I don't like NAB flexing its well-funded muscle, they have plenty of technical reasons to oppose this. Once again the FCC is trying to take the easy way out and shoehorn incompatible services where they shouldn't be. Either do it right and allocate dedicated spectrum or don't do it at all. |
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| said by rf_engineer:said by fifty nine:The problem is what is a vacant channel. Exactly. A receiver can't notify its reception of a channel to whitespace devices in the area. And unless the whitespace device has exactly the same antenna as a potential interference victim, oriented the same way, and has the same receiver sensitivity, it can never identify a vacant channel with 100% certainty. Filtering is useless if the interference is co-channel. While I don't like NAB flexing its well-funded muscle, they have plenty of technical reasons to oppose this. Once again the FCC is trying to take the easy way out and shoehorn incompatible services where they shouldn't be. Either do it right and allocate dedicated spectrum or don't do it at all. The FCC hads defined standards as to what a vacant TV channel is! The fact that by putting up a mega TV antenna on a tall tower you can pick up stations out of their market area is irrelevant. Each TV station is licensed to cover a specific area and market. Outside those areas is free game for 'white space' devices-and should be! |
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| reply to fifty nine
use some more jargon to give the impression you know what you're talking about, I'm super impressed. Your "technical" posts don't even properly explain why Whitespace Broadband is bad. FAIL |
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| said by batch :
use some more jargon to give the impression you know what you're talking about, I'm super impressed. Your "technical" posts don't even properly explain why Whitespace Broadband is bad. FAIL
Merely saying "FAIL" proves nothing. Counter his posts with some technical material explaining why he's wrong. |
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| reply to qworster
said by qworster:The FCC hads defined standards as to what a vacant TV channel is! The fact that by putting up a mega TV antenna on a tall tower you can pick up stations out of their market area is irrelevant. Each TV station is licensed to cover a specific area and market. Outside those areas is free game for 'white space' devices-and should be! The FCC defines reception contours by different "grades" and markets by Nielsen Media research's "Designated Market Areas" or "DMAs." One isn't usually a subset of the other, due to terrain and the like. But out in the fringe we still manage to get reception.
The fact that I need a roof antenna to receive anything at all is inconsequential to the fact that I'm in the NYC DMA. Your desire to download pr0n shouldn't trump my ability to watch TV. You have alternate means like Cable, DSL and existing WISPs that use other frequencies and technologies. |
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| reply to batch
said by batch :
use some more jargon to give the impression you know what you're talking about, I'm super impressed. Your "technical" posts don't even properly explain why Whitespace Broadband is bad. FAIL
So why don't YOU explain why it will work, despite the fact that Google's and Microsoft's equipment failed during FCC tests, yet the FCC went ahead and approved them anyway. |
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 jhboricuaExMod 2000-01
join:2000-06-06
Minneapolis, MN | said by fifty nine:So why don't YOU explain why it will work, despite the fact that Google's and Microsoft's equipment failed during FCC tests, yet the FCC went ahead and approved them anyway. Are you referring to the rigged tests back on August?
My understanding is that in the one that was performed later on October, all the tested devices satisfied the requirement of >90% probability of detection for occupied channels while at the same time achieving a high probability of identifying unoccupied channels. |
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| said by jhboricua:said by fifty nine:So why don't YOU explain why it will work, despite the fact that Google's and Microsoft's equipment failed during FCC tests, yet the FCC went ahead and approved them anyway. Are you referring to the rigged tests back on August? My understanding is that in the one that was performed later on October, all the tested devices satisfied the requirement of >90% probability of detection for occupied channels while at the same time achieving a high probability of identifying unoccupied channels. Here's an idea. Why don't we test them at a political convention, or maybe one of BO's speeches on the economy.
You know, just to make sure. |
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jhboricuaExMod 2000-01
join:2000-06-06
Minneapolis, MN | said by fifty nine:Here's an idea. Why don't we test them at a political convention, or maybe one of BO's speeches on the economy. You know, just to make sure. Works for me.
My point still stands, my understanding is the devices in question passed, not failed, the FCC tests on October 2008, and then they were approved later that year. If so, your claim that they failed and got approved anyway is false.
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"Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe." - Albert Einstein
Jose A. Hernandez * System Admin * MPLS, Minnesota, USA * |
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1 edit | Lab tests aren't really representative of the real world, as was proven by Ed Hare of ARRL with BPL.
Basically the FCC is rolling the dice and letting the electronics manufacturers not interfere and they are enforcing that with the honor system.
Now if you are a user of HF radio spectrum you will know that the honor system doesn't work. Just wait till your neighbor buys that new plasma TV. |
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| reply to qworster
said by qworster:said by rf_engineer:said by fifty nine:The problem is what is a vacant channel. Exactly. A receiver can't notify its reception of a channel to whitespace devices in the area. And unless the whitespace device has exactly the same antenna as a potential interference victim, oriented the same way, and has the same receiver sensitivity, it can never identify a vacant channel with 100% certainty. Filtering is useless if the interference is co-channel. While I don't like NAB flexing its well-funded muscle, they have plenty of technical reasons to oppose this. Once again the FCC is trying to take the easy way out and shoehorn incompatible services where they shouldn't be. Either do it right and allocate dedicated spectrum or don't do it at all. The FCC hads defined standards as to what a vacant TV channel is! The fact that by putting up a mega TV antenna on a tall tower you can pick up stations out of their market area is irrelevant. Each TV station is licensed to cover a specific area and market. Outside those areas is free game for 'white space' devices-and should be! But does the FCC definition meet what consumers would consider vacant? Reception of out of market stations, especially independents, has been an added benefit to consumers for years, so this essentially takes away a benefit to the public. Cable subscribers enjoy this benefit today. (As if it's not bad enough for OTA viewers getting a few channels, let's get rid of the few out of market stations they enjoy...  ) Furthermore, DTV coverage compared to legacy analog coverage is quite lousy. Ironically at my home two out of market ABC affiliates have stronger calculated DTV signals than the in market ABC affiliate. Luckily I have cable. Much of this hinges upon how conservatively or liberally the FCC manages the database entries. But from a technical standpoint, which was the original trust of this thread, cognitive channel selection is full of problems. |
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