Y'know, there is some relevance in a significantly asynchronous circuit with this stuff.
Put the High speed TX on the top of the mountain and have it push high speed frames in broadcast or multicast mode whilst the outlying stations listen to the stream and write down the packets relevant to them. The outlying stations could then be polled for traffic and would respond at a lower speed on another frequency. Whilst the net effect would be as though the whole network were working at (say) 3mbps at least it would be reliable and sove issues like hidden transmitter etc.
This has been thought of before I'm sure.
On Fri, Sep 1, 2017 at 5:32 AM, Ron Economos w6rz@comcast.net wrote:
Well aware of digital ATV, I'm the developer of the digital television component of GNU Radio. The DVB-T2 DSP code was developed by myself and Charles G4GUO. The DATVExpress transmitter board (that G4GUO is one of the developers on) could be used for this project along with many other transmit capable SDR's. However, the Ettus B2x0 is known to have the best phase noise performance on microwave frequencies.
The cheap DVB-T dongles can work, but the latency of DVB-T is not controllable due to a fixed "PHY" frame size. In DVB-T2, the frame size can be made very small and this works wonders for latency. Currently, I'm using a 3.458 millisecond frame size out of a maximum of 250 milliseconds. However, short frame sizes sacrifice throughput for latency.
The DVB-T2 receiver I'm using is not too expensive, only $69.
http://www.hauppauge.com/site/webstore2/webstore_pctv292e.html
The transmit functionality is accomplished by having an instance of Pcap running in the GNU Radio ULE block. All the IP packets sent to the normally receive only dvb0_0 interface are captured by Pcap before they go to the bit bucket.
Ron W6RZ
On 09/01/2017 01:40 AM, Rob Janssen wrote:
Very interesting indeed! You are probably aware that there is some activity on Digital ATV and the boards made for that purpose (and/or the cheap dongles they use) could be used for this as well. We have a Digital ATV repeater here that is currently under some reconstruction, and I have suggested putting some IP broadcast on the multiplex. Indeed, as you note, a Linux-based DVB receiver can easily put the demodulated and extracted IP traffic on its LAN interface. More than a decade ago I did some "experiment" logging the downlink of satellite-internet on a Dreambox and it just used standard features of its software. But your test of using this full-duplex (rather than just unidirectional as it was envisioned) surely is innovative.
It could be useful here as well, indeed as you indicate to make links on amateur bands for which there is no commercial WiFi equipment. It is not straightforward to use that equipment with transverters, and a steady fullduplex link would certainly be easier.
Some people are also working on a 70cm digital access with smaller bandwidth, there is little detail on what modulation they use, it would be interesting to see if using DVB-T2 in halfduplex more is feasible. Probably not, due to high turnaround delays.
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