high data throughput recommended standard nasa presentation to ccsds optical communications working...
TRANSCRIPT
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High Data Throughput Recommended Standard
NASA Presentation to CCSDS Optical Communications Working Group
11 November 2014
11/11/2014
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Space Relay ArchitectureUser Segment
A
B/A
A
A
A
B/A
Relay Segment
SpaceUser
AirborneUser
GroundUser
SpaceRelay
SpaceRelay
GroundRelay
GroundNetwork
Primary near term interest is in relay architecture for conveying data from user to terrestrial ground network
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Scalable, Extensible Architecture
• Architecture should support efficient high-rate data transfer to/from space, air, and ground users
• Signaling should support functions such as channel state monitoring and switching/routing at the GEO terminal
• Data rate should be variable to support a wide variety of users and missions– Near term goal: few Mbps to several Gbps
• Data rate should be scalable to support future high-rate (>10 Gbps) users
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Power Efficient System Design
• Bandwidth expansion (e.g. from modulation and/or coding) should be used efficiently to improve link performance– Reduces SWaP and cost of terminals– Allows future scaling to higher data rates
• Space-relay and/or Direct-to-Earth architectures enable use of capacity-approaching coding techniques, since high-complexity decoding may be performed at ground terminal
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Fiber Telecom Wavelength
• Leverage commercial terrestrial telecom investments at 1.55 µm– Large global vendor base offering wide selection of high
performance components– Current trend toward higher levels of photonic and electronic
integration and more sophisticated optical signal processing for telecom applications expected to benefit space applications
– Enables future data rate scaling using WDM and other telecom approaches
• Vast majority of U.S. lasercom investments and demonstrations are at 1.55 µm
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High Rate Signaling Overview
Encapsulation (HDLC)
FEC (DVB-S2)
Channel Interleaving (optional)
Physical Layer Framing RandomizerQ-Repeat
Input from Link Layer(e.g. Ethernet orCCSDS frames)
To amplifier ortelescope
Modulation
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Encapsulation• Frames at terminal input are encapsulated using HDLC• Rationale:
– Provides transparent interface between bursty/asynchronous source frames and synchronous modem
– Supports many input frame protocols (e.g. Ethernet, CCSDS, etc.)– Industry standard, based on RFC 1662
0011111011111111
16 bits
Protocol HDLC Payload
Variable
FCS
32 bits
Flag
8 bits
01111110Address
8 bits
Control
8 bits
00000011Flag
8 bits
01111110 Inter-frame Fill or next Address
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Forward Error Correction• Links primarily utilize ½-rate DVB-S2 code
– BCH outer code + LDPC inner code• Other DVB-S2 code rates may be used with coordination between
user and ground relay• Rationale:
– Industry standard, based on ETSI EN 302 307– Excellent power efficiency
BCH LDPC
64,800 code bits
32,400code bits
32,208 source bits
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Channel Interleaving• Channel interleaver is used for all links going through the Earth atmosphere• Convolutional bit interleaver with data-rate dependent parameters• Rationale:
– Mitigates effects of atmospheric fading cannel– Convolultional interleaver requires ½ memory of equivalent performance block
interleaver
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Q-Repeat• For lower data rate modes (<51 Mbps), individual (interleaved)
codewords are repeated Q times during transmission• Rationale:
– Enables low data rate links– Limits dead time from burst-mode DPSK
Interleaved Codeword (64800b)
Q-RepeatInterleaved Codeword (64800b)
Interleaved Codeword (64800b)
Interleaved Codeword (64800b)
Codeword repeated Q times
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Physical Layer Framing• 1024-bit header is appended to each (interleaved) codeword at
physical layer– Unique ID for synchronization, content specification, channel state
monitoring– Remaining bits may be used for channel state information, frame
sequence counters, physical layer control, etc.• Header contents may be encoded separately from payload data
with a code that may be processed at space relay• Rationale:
– Enables physical layer synchronization– Enables multiplexing and switching at physical layer in relay nodes
Unique Word (384b) Interleaved Codeword (64800b)Channel State,
FSN, etc. (640b)
1024-bit Header11/11/2014
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Randomizer• Based on LFSR, 1 + x + x3 + x12 + x16, initialized to 0xFFFF at beginning
of frame• Unique word portion of frame is not randomized• Rationale:
– Reduces likelihood of long runs of 1’s or 0’s in transmitted sequence
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Modulation
• Differential phase shift keying at slot rate of 2.88 GHz• Data transmitted in bursts of 176 bits. Deadtime between
bursts varied to change data rate• Rationale:
– DPSK provides good power efficiency with low-complexity incoherent receiver
– Burst mode is compatible with average-power limited transmitters– Enables low-complexity multi-rate transceivers
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Modulation
p p p p … p p p p p … p
h1
p
176 channelbits
Dx176 emptybits
64768 channel bits (368 bursts of 176 channel bits)
e e … e
… p
Dx176 emptybits
h1
p
…
p
hN
p p
176 header bits
e e … e
…
Dx176 emptybits
p p p p
176header bits
…
Dx176 emptybits
p p p
144 headerbits
b1 b2
p
…
p
bN
p p
176 channelbits
1024 header bits
1024 header bits
h1
p
h2
p
…
p
hN
p
b1
p
b2
p
…
p
bM
p p
b1
b2
p
…
p
bM
p p
h1
pp p p p p p p p p p p p p p
64800 channel bits
pp = Optical Pulsehihn = Header Bit b
ibn = (Encoded/Interleaved) Channel Bit
de = Empty Bit (Off-Time)
p
h1 … hN h1 … hNe e … e
e e … eb1 b2 … bN e e … eb1 b2 … bN
h1
p
…
p
hN
p p
176 header bits
e e … e
…
Dx176 emptybits
p p p p
176header bits
…
Dx176 emptybits
h1 … hN e e … e
1D
RateMax
RateMax h1 hN…h2 b1 b2 … bNb3 b4 b5 b6 h1
p p p p
176header bits
…
Dx176 emptybits
h1 … hN e e … e
p p p p p …
e e … eb1 b2 … bN
176 channelbits
Dx176 emptybits
b1 … bN
p pp p
32 channelbits
64800 channel bits
32 channel bits (from previous burst)
e
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Summary of Data Rate Modes
Mode Name User Data Rate (Mbps)
Q Repetition
Interleaver N
Interleaver B (bits)
U-1244 1244 (Max) 1 162 96,000
U-622 622 (Max/2) 1 162 48,000
U-311 311 (Max/4) 1 162 24,000
U-155 155.5 (Max/8) 1 162 11,200
U-51.8 51.8 (Max/24) 1 162 4,000
U-16 16 2 162 1216
U-8 8 4 162 608
U-4 4 8 162 288
U-2 2 16 162 128
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Wavelength• Separate transmit, receive, acquisition wavelengths• Selected from ITU-T G.694.1, v.2.0 (2012-02-13)
– 50-Ghz spacing, fixed grid– Optical C-band (1530-1565 nm)
• A/B terminal specification determines transmit and receive wavelengths in system architecture
• Rationale:– Allows leveraging of current and future telecom industry technology
developments– Large potential vendor base– Enables eventual data throughput scaling using industry-standard
wavelength division multiplexing
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Relay Link ExampleApplication
Transport
Network
Link
LAN HDLC
FEC/ILV/ Q-Repeat
Physical Link
User Platform
User Terminal
Phy Frame
Relay Platform
Relay Terminal 1
Phy FrameRelay Terminal 2
Physical Link
HDLC
Ground RelayNetwork
Link
Ground Network
Switch
Optical relay serves as a transparent link-layer bridge between User Platform and Ground Relay
Phy Frame
Random
Modulation
De-Random
De-Mod
Random
Modulation
FEC/DeILV/ De-Q-Rep.
Phy Frame
De-Random
De-Mod
Transparent Bridge
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