XPost: comp.dsp, sci.crypt, sci.electronics.design
From: NotaBrewster@thebarattheendoftheuniverse.org
On Mon, 21 Dec 2009 15:11:34 -0500, Jerry Avins wrote:
>Eric Jacobsen wrote:
>> On 12/21/2009 12:42 PM, Steve Pope wrote:
>>> Eric Jacobsen wrote:
>>>
>>>> On 12/20/2009 3:42 PM, Steve Pope wrote:
>>>
>>>>> A rate 1/2 coded system operating at an Eb/No of +2 dB has the
>>>>> same raw BER as an uncoded system operating at an Eb/No of -1 dB.
>>>>>
>>>>> A rate 1/3 coded system operating at an Eb/No of +3.77 dB has
>>>>> the same raw BER as an uncoded system operating at -1 dB.
>>>
>>>>> (Unless I'm confused, which has happened before...)
>>>
>>>> Doh! I think I went the wrong way with the 3db and 4.77dB differences.
>>>> I get stuff like that backwards all the time.
>>>
>>> Okay, we're in sync, even if our hypothetical modem isn't.
>>>
>>>>> I'm not too skeptical. I would posit that GSM phones in their
>>>>> basic 2G mode operate under conditions this bad, and 802.11 systems
>>>>> at 1 mbps might also.
>>>
>>>> I'm less skeptical now. ;)
>>>
>>> Right.
>>>
>>> The AWGN channel exhibiting 10% raw BER is still 3 dB less noisy than
>>> rate 1/3 BPSK capacity, and popular binary convolutional
>>> codes generally start functioning when you're 2 dB to 3 dB from capacity.
>>>
>>> The near-channel-capacity codes are generally functional around 1 dB
>>> from capacity, sometimes less.
>>>
>>> Steve
>>
>> Yeah, we're on the same page. Since the context was a satellite link,
>> I'd still be skeptical that anyone would bother to use an R = 1/3 code
>> over a satellite, just because of the spectral efficiency (since
>> transponder bandwidth is muy expensive). For R = 1/2, which is more
>> believable, my skepticism remains healthy.
>
>Remember: this is military money. Those birds are $30 million a pop.
>
>Jerry
Yer nuts. Satellites are $400 million each, and that is a commercial
bird!
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