2 Sep
2017
2 Sep
'17
6:44 p.m.
OFDM is about as good as it gets with regards to multipath. Right now to
reduce latency, I'm using the 4K carrier mode (3409 active carriers)
which has a symbol duration of 448 microseconds (in 8 MHz bandwidth).
That means a reflection from less than 134 km away will be in the same
symbol.
DVB-T2 has six carrier modes. 1K, 2K, 4K, 8K, 16K and 32K. 1K is used
for high Doppler applications (mobile) and 32K is used for high
multipath. Almost all DVB-T2 television transmitters in Europe and Asia
use the 16K or 32K mode. The BBC uses 32K for their multiplexes in the UK.
The new proposed US digital TV standard, ATSC 3.0, is almost identical
to DVB-T2. It's basically DVB-T2 with some tweaks added to get another
dB of S/N performance.
Ron W6RZ
On 09/02/2017 10:29 AM, Brian Kantor wrote:
Unless they've come up with a modulation scheme
which overcomes the
multipath distortion of transmitted symbols, I believe line of sight is
practically a necessity.
But I'll be the first to admit that my communications theory knowledge
is now many decades old. Perhaps there is a way around it.
- Brian