[Ground-station] P4B Regenerative Repeater Likelies

[Michelle Thompson]

Thank you Wally. This is an excellent summary and greatly helps define
remaining work.

Questions and comments? Bring 'em on.

-Michelle W5NYV




On Sat, Mar 2, 2019 at 2:31 PM Wally Ritchie via Ground-Station
<ground-station at lists.openresearch.institute> wrote:

> I've begun some work on an Internet based simulator for a p4b geosat. It
> focuses on the Narrowband Multiplexor entity that relays the data from the
> uplinks to the DVB-S2 downlink. (More on this in a few days in another
> thread).
>
> In the process I've collected a random assortment of "sort of consensus"
> thinking as I recall it from the slack channels over the last year or two.
>
> Please comment here or on slack regarding any that are not actual likelies
> or are not understood.
>
> Wally WU1Y
>
>
> 1. The Downlink will likely have power output of 10W – 100W into a
> hemispherical beam.
> 2. The Downlink will likely have symbol rate of 1 Mbaud to 10 Mbaud.
> 3. The downlink will likely have a saturated and unfiltered final.
> 4. The downlink will likely provide a DVB-S2 carrier.
> 5. The downlink will likely use GSE supporting multiple streams and
> ACM/VCM.
> 6. The primary stream will likely be a flow of UDP broadcast packets at 25
> pps. These will carry the relayed narrowband channel data and system data.
> 7. System data will likely include both telemetry and operational data
> (e.g. logs) and will be unencrypted except where necessary.
> 8. A narrow band multiplexor (NBM) entity will likely combine the system
> streams and the relayed narrowband channels into a single UDP packet flow
> which will have priority over other flows.
> 9. Wideband channels will likely be supported and relayed in separate IP
> packet flows (or perhaps repeated BBFRAMES).
> 10. System data may in some cases utilize separate IP packet flows.
> 11. Narrowband uplinks will likely be handled by a multi-channel receiver
> with 64 – 128 channels spaced at 25kHz (or somewhere between 12.5 to
> 75kHz). Note that with 64 25kHz channels the narrowband input spectrum
> would be 1.6MHz.
> 12. Earth stations will likely require a sub-ppm accuracy station clock
> with Frequency Accuracy and Stability on the order of 100ppb for 25kHz
> channels. The clock may have to be synchronized to the downlink. Note that
> 1ppm at 5GHz corresponds to 5kHz frequency shift.
> 13. Uplinks will need to control power output, frequency, and timing to
> arrive in their assigned uplink slot.
> 14. Narrowband Uplink modulation will likely be some form of GMSK or QPSK
> and could vary over the lifetime of the repeater.
> 15. Narrowband Uplink PSD will need to maintain power in the adjacent
> channels below specified tbd limits.
> 16. Uplink spurious outputs both in-band and out-out of band will need to
> be kept below specified tbd limits.
> 17. The possible (and wildly optimistic) presence of other satellites with
> 5GHz uplinks as close as 2 degrees should be recognized.
> 18. Narrowband Uplink transmissions will likely be framed in 40ms slots
> matching the NBM frame rate.
> 19. Narrowband Uplink symbol rates will likely be on the order of 5000
> baud to 2000 baud for 25KHz channel spacing.
> 20. Narrowband Uplink transmissions from active stations will be
> continuous back to back frames. Where the frame does not carry relayed
> speech (e.g. silence intervals) identification or alternate data may be
> transmitted and relayed.
> 21. Frames containing station identification will likely be FEC coded
> (e.g. Golay Coding).
> 22. Preambles on each frame will likely be required for synchronization
> and adaptive equalization.
> 23. Longer preambles may be required on the initial frames of a
> transmission.
> 24. Identification will likely be required on the first frame of a
> sequence and periodically during a continuous sequence.
> 25. Data within a frame will only be relayed through the NBM when fully
> conforming to the rules.
> 26. Where the receiver is unable to synchronize and decode a frame,
> parametric data related to the transmission will likely be substituted for
> the missing payload.
> 27. Dedicated channel sets on both band edges will be used for testing and
> commissioning.
> 28. Stations will not be permitted to transmit on regular channels until
> they have been commissioned using automated procedure that take place using
> the commissioning channels. Any transmission by an un-commissioned station
> will be considered intentional interference.
> 29. A cease transmission command will likely be provided in the NBM output
> requiring all stations to immediately and temporarily cease transmission.
> This might be used to support processes to identify and locate interference
> or unauthorized transmissions.
> 30. Commissioning will likely involve short transmission bursts on the
> order of 3 to 5 frames in a test channel. Commissioning transmissions will
> likely be separated in time (many seconds for an individual station).
> 31. Commissioning channels will likely dedicate one or more adjacent guard
> channels to be used in the commissioning process (e.g. proving adjacent
> channel power, frequency, and frame alignment measurement to verify that
> the station is within tbd limits.
> 32. Allocation of a commissioning channel to a station will likely involve
> a fair hash algorithm based on offered demand and capacity. Transmission
> Collisions will be possible and expected during commissioning.
> 33. Allocation of channels to commissioned stations will likely use a
> channel allocation protocol operating within single channels (as opposed to
> the multiple channels used for commissioning/test). Note that a station
> cannot be identified until its transmissions can be decoded by the
> receiver.
> 34. Once a station is able to transmit a compliant signal in the
> commissioning channel it will acquire a secure access token through
> interaction with the server. This will likely involve authentication. The
> token will be used to identify the station in transmissions. The receiver
> will likely substitute the station's actual callsign for the token in the
> downlink.
> 35. The NBM output configuration will likely be flexible allowing for a
> variable number of active uplink channels of various payload rates with an
> aggregate relayed payload on the order of 256kps.
> 36. The NBM will likely support Nx800 channel allocations with N <= 12
> (i.e. 800 to 9600bps).
> 37. During any given frame (UDP packet), an NBM channel segment may carry
> Uplink Payload, Uplink Identification (Station ID and payload type),
> Parametric Receiver Data, or System Data.
>
>
>
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