Posts by F4HDK


    1) A kind of PACSAT BBS or HamNet access

    as described above...

    About the point 1, a short term solution for IP/Hamnet over QO-100, what do you think about my proposal to port my NPR protocol to QO-100 WB, like described in my previous post? Do you find that it would be useful or not?

    2) A successor for P4-A which would replace the Analog Linear Transponder Downlink by a regenerative digital transponder with a single DVB-S2 downlink.

    About the point 2, it is similar to what P4B, in the USA, planned to do a few years ago.

    In my opinion, it is far from optimal (it's only my opinion):

    - A pure "bend pipe", like QO-100, is much better for experimenters like us, in order for evey motivated OM to experiment new things on his own.

    - The number of simultaneous TX stations is (very) limited.

    Part of the Uplink would be still "linear" as it is for SSB/CW/etc., but just like a remote SDR which will stream the "passband" down as I/Q data on the DVB-S2 downlink.

    Another topic about "point 2" I’ve not understood the "narrow band SDR" that you propose, inside the satellite. If you want to capture 100kHz RF bandwidth at uplink side, then you need more than 24bits x 100kHz= 2.4Mbps for IQ samples of each channel, for 12bits IQ sample resolution, to the downstream. This induces a huge RF bandwidth need at downlink (~2MHz with QPSK) compared to a pure “bend pipe” solution (~100kHz). Therefore, unless I have not understood something, I don’t think that it’s a good idea.

    73, Guillaume F4HDK


    I'm the inventor of "New Packet Radio" (NPR), take a look here:

    My thoughts about the discussion:

    DVB-S(2) is only well suited for a continuous stream of data at constant bitrate. It's not well suited for burst IP trafic, like we have most of the time when we use IP (web page browsing, e-mail exchange, text tchat). Especially when we consider uplink trafic (from users to servers) for dozens of users, then dozens of constant bitrate channels become a waste of precious radio ressources.

    I think I could adapt my NPR protocol (which already transports IP over radio) in order to fit on a portion of the QO-100 WB transponder. It would need lots of modification, but it should be feasible. We could name it "NPR-VSAT".

    It could be MF-TDMA (Multiple Frequencies Time Division Multiplexing Access), therefore using multiple timeslots inside multiple frequencies/chanels (for example 5 chanels, each 200kHz wide). Stations would transmit by bursts (instead of continuously for DVB-S2).

    A central station (the satellite hub) would allocate dynamically (in real time) these ressources (frequencies and timeslots) between users, according to their need.

    All this would be SDR-based, I will try the Adalm Pluto and Lime SDR Mini. The topology could be full-mesh, multipoint to multipoint.

    Each user station would transmit on one single frequency at a time (switching fastly between frequencies when needed), and each user station would listen to all frequencies/chanels simultaneously (with one single SDR, it should be feasible).

    It would be more efficient than pure DVB streams because of the "burst" type of trafic.

    The modulation scheme would be probably less efficient than DVB-S2: 4-levels GMSK seems easy to implement for burst radio frames.

    But all together, I still see a great overall improvement compared to the DVB-S2 uplinks initially proposed.

    We could even associate it with one single IP-over-DVB downstream channel from the central satellite hub point (Bochum?), in order to optimize the "server to client" trafic.

    I agree with DL4OCH : This downstream could even share a single DVB-S2 carrier/chanel with the existing "beacon video".

    - "Hub to user" trafic would be IP over DVB.

    - "User to user" and "user to hub" IP trafic would be NPR-VSAT.

    Tell me what do you think about this ambitious idea.

    Do you think it could be usefull that I work on such a project?

    Do you accept other modulation scheme than DVB over QO-100 WB?

    If we start working together, it would take a lot of time developing such a project, probably more than one year, but I think it’s feasible (not 100% sure yet). For example, it took me 2 years to develop NPR: 1 year for having a proof of concept, and 1 additional year to reach a useable solution.

    I'm currently quite busy with my NPR-70 project, but I could start working on this QO-100 project rapidly.

    And that's really the kind of thing I like to develop!

    Do you know if someone else has already begun to work on an equivalent project?