Hopefully this isn't too far off topic. I've just completed testing of
an OFDM modem using IP over DVB-T2. It uses an SDR transmitter and a
commercial DVB-T2 receiver to implement the RFC 4326 Unidirectional
Lightweight Encapsulation (ULE) for Transmission of IP Datagrams over an
MPEG-2 Transport Stream (TS). ULE is supported in the Linux kernel for
DVB receivers.
https://tools.ietf.org/html/rfc4326
It's a full-duplex modem capable of up to 50 Mbps (in both directions)
in an 8 MHz bandwidth. The current test bed consists of an Ettus B200
SDR transmitter, PCTV 292e DVB-T2 USB receiver, Kuhne down converters
for 13cm and 9cm, Microlab BK-26N diplexer and RFSpace TSA600 Vivaldi
antenna.
http://www.w6rz.net/IMG_0119.jpghttp://www.w6rz.net/traceroute.png
The transmitter is based on the DVB-T2 transmitter in GNU Radio and uses
this OOT module for the ULE protocol.
https://github.com/drmpeg/gr-ule
To reduce the latency, I've merged the DVB-T2 blocks to avoid having so
many buffers between blocks.
https://github.com/drmpeg/gr-dvbt2ll
Current test frequencies are 2305 and 3429 MHz with an 8 MHz bandwidth.
The bit-rate is 28.6 Mbps (symmetrical).
It's intended to replace commercial WiFi equipment for amateur WAN
interlinks.
Advantages:
1) Full-duplex. Adding power amplifiers, preamps, diplexers/duplexers is
easy.
2) Frequency agile. Can work on any band above 420 MHz. 70cm through 5cm
direct TX from the SDR and millimeter frequencies with an up-converter.
3) Bandwidth agile. 5, 6 ,7 and 8 MHz bandwidths.
4) May be legal on 70cm. Although I haven't implemented it yet, a small
portion of the bandwidth can be used to send a low-rate video stream
(for example, a still picture of your call sign for ID). This would
classify the emission as digital ATV, not data.
Disadvantages:
1) Latency is a bit high. It's currently 100 ms (200 ms round trip).
This is a function of buffering in GNU Radio and the USB 3.0 connection
to the SDR. An FPGA implementation of DVB-T2 and a different SDR
architecture could solve this.
2) Cost. It's difficult to compete with commercial WiFi equipment.
However, lower cost components can be used instead of the "Cadillac"
test bed I constructed. For example, a ADALM-PLUTO at $99 could be used
instead of the Ettus B200 for transmit. Two antennas instead of a
diplexer and lower cost down-converters than the Kuhne units.
3) Requires a Linux computer to run it. An Odroid XU4 may be adequate,
but I haven't tested it.
73,
Ron W6RZ
John,
I was hesitant at first. Mostly because I think you are an okay guy.
While my message might seem poor in taste, I stand by it.
I feel if you are going to play the arm chair lawyer part, then you
should be more transparent with your role with NW Digital. I don't
see you pointing out other rules issues, just things in those two
areas, which ironically are directly related to NWdigital.
I do applaud your recent AMBE effort, offering a discount on the xlxd
list to aide development efforts, rather than the usual approach.
Moving forward I'd like to see less poo-pooing, and more doing not
just on this list, but though out the hobby. Folks are expected to
know the rules are part of their entrance test into the hobby. I am
not an official observer, nor a lawyer, and suspect the same is with
you. We have no obligation to remind others that obligation is on
each operators shoulders alone.
If you want to do things that help NWdigital, I don't have a problem
with you becoming the person to spear-head a more aggressive data
rules overhaul proposal to the FCC. This is because its not just
beneficial to NWDigital, but to amateur radio as a whole. I can't
speak for others on this however, as I am sure operators of other
modes may feel differently. I do encourage you to survey the odds and
consider working in this positive manner to have these modernized,
over the "old-man get off my lawn approach" that I have seen.
Now on to a new subject that is more productive please.
73
Steve, KB9MWR
