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Old 04-02-2008, 02:49 PM
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Question Output power varies with transmission throughput: why?

Hi!

There's something I'm curious about that maybe you can explain. I've noticed in the datasheet wireless devices the output power is weaker when using higher transmission throughput. Why is that?

Compliments,

Rodrigo S.
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Old 04-21-2008, 11:47 AM
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Does anyone knows the answer to this question, please?
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Old 04-21-2008, 05:24 PM
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Can you provide a link to one of these datasheets?
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Old 04-21-2008, 06:04 PM
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Talking

Quote:
Originally Posted by Rob02 View Post
Can you provide a link to one of these datasheets?
Sure, Rob02, here it is. See the Output Power/Receive Sensitivity:.

I believe it has to do with the used modulation. I would like to hear the technical explanation.

I have a theory... but only that, an unfunded theory.
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Old 04-21-2008, 06:51 PM
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Looking at that pdf I would say that the quoting of 2 different power levels for the a and g modes is due to the card operating in non-turbo and turbo mode, it probably requires more power to operate in turbo mode hence it has a reduced power output.

It is well known that receive sensitivity is reduced as data rate increases.
There is an old paper on range versus rate you may wish to read:-
http://www.nativei.com/~heegard/papers/RvR.pdf
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Old 04-21-2008, 07:04 PM
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Well, the two different power levels appear to different throughput's, only 6 and 54Mbps. If it was because of turbo-mode, I believe it would appear at data rate of 108 Mbps, for example.

The thing that must change between throughput's it's the modulation. The "basic" modulation give us smaller throughput's, and the more complex better throughput's. The sensitive has to do with the modulation... since the simpler/basic modulation it's more robust, the receiver can decode until smaller received power. When using more complex modulations, like OFDM for 54Mbps in 802.11a and b, it must receive a better signal to decode correctly. My theory it's that at higher output power, the transmitter hardware will produce such interference that will prejudice the generated signal. So, because the higher throughput generated signal is complex and sensitive, it must be used a lower power output. Does this make any sense?

Thank you for the paper. I'll read it!


Best regards,

Rodrigo
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Old 04-21-2008, 07:35 PM
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I think you are misinterpreting the datasheet. Manufacturers quote data rate against sensitivity not against o/p power e.g http://www.digchip.com/datasheets/do...ISL36356A-APDK
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