Fox-1E (RadFxSat-2) Telemetry and Whole Orbit Data Simulation. Burns Fisher, W2BFJ Carl Wick, N3MIM

Transcription

1 Fox-1E (RadFxSat-2) Teemetry and Whoe Orbit Data Simuation Burns Fisher, W2BFJ Car Wick, N3MIM 1

2 Review: Fox-1 DUV Teemetry Fox-1A through Fox-1D are FM Repeater Sateites» Ony a singe downink frequency» Teemetry sent as DUV» There is a high speed mode too DUV = Data Under Voice» Essentiay FSK at a sow rate (200 bps) FSK on FM?» What happens when you shift the frequency on FM?» Demoduated wave varies according to the carrier frequency shift» So FSK adds sound to the audio beow 2-300Hz 2

3 Review: Fox-1 DUV Teemetry DUV = Data Under Voice» Essentiay FSK at a sow rate (200 bps)» In baseband (audio) it appears as a signa under 300 Hz Hz CTCSS Tone Voice Upink Teemetry Voice Downink 3

4 Review: DUV Data Frame This is what a DUV frame ooks ike Takes about 5 seconds to send About 1000 bits, incuding 32 check bytes for Forward Error Correction, and 8b10b encoding Header Sateite Number Sateite Time Frame Type Payoad FEC Check Bock 4

5 Review: Forward Error Correction FEC designed by Phi Karn, KA9Q et a» (See citation in this paper in the Proceedings)» Uses Reed Soomon (255,223) Send 255 bytes, of which 223 are data (32 check info) Do not use a 223 bytes! Designed for typica fades seen in our expected packets (we coud have made them onger) One 32-byte check bock suffices for one DUV frame 5

6 Review: 8b10b encoding Each byte is transmitted encoded as 10 bits Encoding designed so there are never more than a few bits of the same poarity in a row Avoids a DC spectra ine Guarantees enough transitions to do cock recover 6

7 Review: Payoad Types There are 4 types of payoad sent on Fox-1A-D: 1. Rea-time heath teemetry 2. Minimum vaue heath teemetry 3. Maximum vaue heath teemetry 4. Science Teemetry Types 1, 2, and 3 a have some common data» For exampe temps, votages Each has some unique data» For exampe MIN and MAX have the time of the ast change» A have various unique status bits 7

8 Fox-1E (aka RadFxSat-2) Teemetry Fox-1E is a 30KHz inear transponder Beacon/Teemetry beow the pass band 1200 bits per second BPSK More data requires more FEC check bocks (intereaved) Sti uses 8b10b encoding Transmitted differentiay, i.e. 0 means the same bit as before, 1 means change bits (or vice versa) 8

9 Fox-1e BPSK Teemetry BPSK = Binary Phase Shift Keying» Essentiay a sine wave whose phase is shifted -10kHz 0 30 khz Teemetry Transponder Passband Downink 9

10 Fox-1E Frames Buit on DUV frames concept Each frame starts with header» Payoad type number becomes frame type number» Each frame type has a fixed order of payoads within Each frame ends with FEC check bocks Each frame is encoded with 8b10b 10

11 Frames and Payoads Fox-1A-D frames and payoads were about the same Fox-1E there is a difference» Frame is sti about 5 seconds» Frame sti has 1 header, 1 (set of) FEC check bocks» But frame contains 6 sets of data caed payoads Fox-1E payoad types are the same as DUV +» Two additiona types, 5 and 6, caed Heath WOD 1 and Science WOD 1 Whoe Orbit Data (more ater) 11

12 Fox-1E Frames Header Sateite Number Sateite Time Frame Type Payoad 1 Payoad 2 Payoad 3 Payoad 4 Payoad 5 Payoad 6 FEC Check Bock 12

13 Frame Types vs Payoad Types Frame type 0 (A WOD):» Payoads Frame type 1 (Rea Time)» Payoads Frame type 2 (Min-Max)» Payoads Frame type 3 (Rea Time Beacon)» Payoads Frame type 4 (WOD Beacon)» Payoads

14 What is WOD? WOD means Whoe Orbit Data What can we do with 6X data rate and not many additiona sensors?» Answer: Send data when in range of a ground station that was coected earier in the orbit But we don t know when there is a ground station!» Answer: Send the same data over and over and over 14

15 How We Do WOD A Foxes have MRAM non-voatie memory» Essentiay infinite write cyces» High toerance to radiation FM Foxes use it for Voice of Fox Fox-1E stores WOD MRAM organized as a circuar buffer Coect data 1/minute and store in MRAM Transmit 31 data packets for each one that is coected 15

16 Ring Buffer Type=Coect Data Read=Send to ground By Muhannad Ajjan - Own work, CC BY-SA 4.0, 16

17 How Much WOD To Save? Surprising Truth» No matter how big the memory, we sti transmit each WOD packet the same number of times (31) Consider:» If we have a sma amount of memory a given packet is sent more frequenty, but does not stay in the S/C as ong and thus does not see as many ground stations» With more memory, a given packet is sent ess frequenty, but spread over a wider area on earth? How much memory use is optima? Car Wick, N5MIM, found out! 17

18 A WOD Simuation-Car Wick We wanted to answer these questions:» How much data shoud be stored on board to ensure a is received on Earth somewhere?» How often must data be transmitted to ensure reception?» What are the driving system factors in a WOD design? 18

19 A WOD Simuation A reaistic simuation of sateite track and WOD system can hep answer these questions.» Start with a known orbit mode to predict orbit paths over a period of time» Add in known ground station ocations» Use the orbit mode and a statistica reception mode to predict when messages coud be received.» Change sateite WOD queue ength and other parameters to find the best soution 19

20 A WOD Simuation Start with a standard NORAD LEO orbit prediction mode to buid an orbit simuation 20

21 A WOD Simuation Add in known ground stations that reguary contribute to AMSAT efforts (bue dots =200+ stations) 21

22 A WOD Simuation Contributing ground stations are highy custered in just a few ocations (NA, W. Europe, Japan) 22

23 A WOD Simuation Simuation provides the footprint of a seected sateite over the earth at any instant To receive a transmission a sateite footprint must overap a station for an entire message Probabiity of actua reception is aso a function of eevation (ange from ground station to sateite) 23

24 A WOD Simuation Actua reception is a statistica function of eevation. Higher eevation higher probabiity of successfu reception of WOD 24

25 A WOD Simuation Likeihood Function used in the simuation. As sateite eevation increases, so does the probabiity of receiving a WOD frame. 25

26 A WOD Simuation Simuation: orbits are predicted for a 24 hour period. Fies keep data on when WOD coud be statisticay received based on concentration of stations and eevation 26

27 A WOD Simuation What-if simuation using a poar orbit 27

28 A WOD Simuation A simuation run takes approximatey 15 seconds on a desktop computer Sateite queue engths are adjusted unti minimum data is ost (never received at a station whie in the sateite queue) Factors are orbit pane (poar orbit is better), distribution of earth stations, ength of queue, number of messages sent per unit time) 28

29 A WOD Simuation Exampe data: accumuated seconds during orbits that a sateite is out of range of any ground station 29

30 The remaining question: What is a good circuar buffer size in the sateite? Is there an optima? 30

31 And the answer?? 31

32 And the answer?? 42!!! 32

33 And the answer?? 42!!! No wait---answer to the wrong question 33

34 And the answer?? The Actua Answer: 150! More made itte difference 34

35 Back to Fox-1E Fox-1E has a circuar buffer than can hod 150 WOD data records That woud be somewhere over 1-1/2 orbits Each one gets sent 31 times over the course of 150 minutes. (Backup: We can command the size arger and smaer) 35

36 Credits Car Wick, N3MIM -- WOD Simuation» See paper in 2017 Symposium Procedings Chris Thompson, AC2CZ/G0KLZ FoxTeem» See GitHub/AC2CZ/FoxTeem Phi Karn, KA9Q et a Teemetry encoding and FEC» See references in W2BFJ 2017 Symposium Paper Mike McCann K2GHZ WOD Initia Proposa» See references in W2BFJ 2017 Symposium Paper Burns Fisher, W2BFJ Fox Teemetry Transmission» See paper in 2017 Symposium Proceedings 36