Nice!
This is the first post in this group showing that people are trying to do something new regarding to HAM radio topics. Thank you for bringing my faith in people back! ;)
This is a very nice project, I'd like to test it but I do not have proper equipment to do this now :( Nevertheless please let me know if I can help you anyhow!
-- Best wishes SQ9PID
Ron Economos wrote:
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.jpg
http://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:
- Full-duplex. Adding power amplifiers, preamps, diplexers/duplexers is
easy.
- 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.
Bandwidth agile. 5, 6 ,7 and 8 MHz bandwidths.
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:
- 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.
- 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.
- Requires a Linux computer to run it. An Odroid XU4 may be adequate,
but I haven't tested it.
73,
Ron W6RZ
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