ground-rxtx / linkbudget

git-svn-id: https://svn.spreadspace.org/mur.sat@150 7de4ea59-55d0-425e-a1af-a3118ea81d4c

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+Protokoll:
+
+self made downlink protokoll:
+
+* intelligenter Image Dump
+* Audio Memory Dump
+* Image Bewertungs Index Dump
+* Telemetrie und Counter Dump
+* random Text-Message Dump (wenn Power da ist)
+
+encapsulated in:
+* CCSDSC Frames
+  GMSK (braucht ~10kHz Bandbreite)
+* BPSK 1000 (QPSK 500)
+* Turbo-Codec (if licencse allowed)
+  Reed-Solomon
+
+alt:
+* Nix, raw data via FSK31 (or hither)
+* Turbo-Phi-Code
+* FX.25
+* AX.25
+(depends on content and configuration Flags)
+
+
+Frame:
+Option 1:
+GMSK(CCSDSC(Data,Reed-Solomon))
+Option 2:
+GMSK(CCSDSC(TurboCode(Data)))
+Option 3:
+BPSK500(CCSDSC(TurboCode(Data)))
+Option 4:
+BPSK500(CCSDSC(Data,Reed-Solomon))
+...
+
+
+
+Protokoll:
+Downlink:
+
++--------------------+-----------------+-------+
+| Data Frame Type ID | Frame Type Data | CRC32 |
++--------------------+-----------------+-------+
+
+
+Downlink Frame Types (Frame Type Data):
+* Memory Area Dump Start (new DumpID (inc) , from Address)
+* Random Text Message Start (new DumpID)
+* Image Data Start Frame (new DumpID, Image ID, from Offset)
+
+* DataDump (current DumpID, Packet ID, Data Length, Data))
+
+* Image Metadata Single Frame (Image ID, file size, Quality Factor, DCT-Coefficients Mean, DCT-Coefficients StdDev, simplified rgb image historgram [3 colours * 64 division * 8 Bytes])
+
+DataDump (current DumpID, Packet ID, Data Length, Data))
+Image Metadata Single Frame\\(Image ID, Quality Factor, DCT-Coefficients Mean, DCT-Coefficients StdDev, simplified historgram)
+
+Note:
+ new DumpId with every "Start"-type frame. Only HARD requirement: dumpid must be different from previous dumpId
+ PacketID increments with every frame and resets to 0 with "Start"-type frame
+ DumpId ensures that DataDump streams can be differentiated if in-between StartFrame goes missing
+
+
+most errors should be corrected by FEC
+if Recieve Error of Frame still happens:
+* rerequest memory area with offset
+* rerequest ImageID (w/offset)
+* rerequest whole Dump by explicitly repeating command (can't request dumpid since they are not meant to be uniqe)
+
+
+Uplink Todo ??
+ ?? ability to resend commands in queue before execute -> QueueSlots and "Insert Command into QueueSlot#" instead of "Append Command"
+      contra argument: fading signal will propably wane slower than it takes to fill command queue. so sending full command queue multiple times is
+      more likely to succeed than sending single commands multiple times.
+
+Uplink Commands:
+* Clear Command Queue
+* Append Command WriteConfigArea (Data, CRC32)
+* Append Command DumpMemoryArea (StartAddress, Length)
+* Append Command WriteMemoryArea (StartAddress, Length, Data, CRC32)
+* Append Command AppendNewTextMessage (Length, Data, CRC32)
+* Append Command GetImageMetaData (from ImageID, NumImages)
+* Append Command GetImage (ImageID, fromOffset, max Data to transmit or 0 for all data)
+* Append Command Send Random Text Message
+* Append Command WaitDuration and switch off transciever (Seconds)
+* Append Command WaitUntil and switch of Transc (TimeOfDay)
+* Execute Command Queue (Num Commands, ExecSeqNum, MAC(Full CmdQueue Contents incl Data . Num Commands . ExecSeqNum))
+
+
+Note:
+ Password should be random and 160 bit long
+ MAC(x) = sha1(password . sha1(x . password))
+ Satellite keeps track of highest last used ExecSeqNum and rejects lower
+ Stored ExecSeqNum get's reset to 0 on CRX Reset-Settings
+
+ single commands usually don't carry CRC checks, because they are only ever executed as a whole cmd queue.
+ so it's enough to have integrity check in the last cmd. This also saves bandwidth.
+ As a side effect, the amound of uplink data to be integrity checked becomes dynamic (i.e. on bad link, just send less commands at once)
+
+To Consider:
+ maybe CRC32 SHOULD be added to every Clear/Append command, and every append command should be ack in TTX,
+ so it can be resend on transmission error and execute command has then higher chance of succeeding ?
+ downside: uplink would be much much slower if (optional) we wait for TTX Acks
+ upside: execute command has higher chance of executing
+
+Never: substitute sha1 of individual crc32 with sha1 of whole contents in execute command
+
+
+Attacks:
+
+ Substitution Attack:
+  should not be possible since MAC is calculated over full CmdQueue contents
+
+ Repeat Attack:
+  should be hard, because Nonces are not reusable, unlesss attacker also manages to reset cpu via dtmf
+
+ Man-In-The-Middle Attack:
+  no two way handshake, so no better than other attacks
+
+ Brute Force:
+  can capture uplink stream and brute fore password at home
+  thus password should utilize full bit range and be sufficiently long e.g. 32 byte random number
+
+ Denial Of Service:
+  If password cracked, nonces can be used up
+  Uplink Channel can be actively jammed
+  Append Command can be inserted after our ClearCmdQueue, making sure ExecuteCmd won't suceed
+
+
+To Consider:
+ Does Arm Cortex M3 have enough speed/power for RSA | DSA | ECC-DSA ?
+
+