[opendtv] Re: Latest S/N test
- From: Bob Miller <bob@xxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 25 Jan 2005 14:02:14 -0500
I am waiting for more info. They did say that the data rates were as
close as possible to 19.3 Mbps for all modulations tested.
Bob Miller
Manfredi, Albert E wrote:
>Bob Miller wrote:
>
>
>
>>Recent test of DMB-T, DVB-T, ATSC
>>
>>S/N
>>18.5 db ATSC OQam Linx
>>16 db DVB-T
>>15 db DMB-T
>>and
>>12.5 db DMB-T using a similar scheme to DVB-S-2
>>with LDPC
>>
>>How close is that to Shannon limit?
>>
>>
>
>Can't tell, unless you give the actual bandwidth used
>in the RF channel and the channel capacity (b/s). With
>that info, the limiting S/N for error-free
>communications can be computed.
>
>Strange that the OAM scheme measured lower than ATSC,
>but again, need more information. When Linx first
>developed that, they claimed 15 dB for the wide
>channel. Perhaps having those two extra pilots,
>while it does increase robustness, also demands more
>power. But they were rather low power. Weird.
>
>If I remember, DMB-T uses a CDMA spread spectrum scheme
>to transmit the training sequence, and COFDM for the
>signal. Not positive, though.
>
>
>
>>So the latest DVB-T compared to the latest 8-VSB
>>gives DVB-T a 2.5 db advantage.
>>
>>
>
>That's doubtful, as it would mean DVB-T is capable
>of 12.5 dB C/N in a 5.38 MHz channel for ~20 Mb/s.
>Perhaps you need to supply more detail on these
>tests. And no silly propaganda, please!
>
>BTW, the Shannon limit for 20 Mb/s in a 5.38 MHz
>channel would be that you need 10.85 dB of C/N
>for error-free comms.
>
>Bert
>
>
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