1. High Data Throughput Recommended Standard
NASA Presentation to CCSDS Optical Communications Working Group
11 November 2014
11/11/2014

2. Space Relay Architecture
User Segment A
B/A
Relay Segment
Space
Relay
Space
Relay
Space
User
Airborne
User
Ground
User
Ground
Network
Ground
Relay
Primary near term interest is in relay architecture for conveying data from user to terrestrial ground network
11/11/2014

3. 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
11/11/2014

4. 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
11/11/2014

5. 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
11/11/2014

6. High Rate Signaling Overview
Input from
Link Layer
(e.g. Ethernet or
CCSDS frames)
Encapsulation (HDLC)
FEC (DVB-S2)
Channel Interleaving (optional)
Q-Repeat
Physical Layer Framing
Randomizer
Modulation
To amplifier or
telescope
11/11/2014

7. 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
11/11/2014

8. 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
Excellent power efficiency
BCH
LDPC
32,208
source bits
32,400
code bits
64,800
code bits
11/11/2014

9. 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
11/11/2014

10. 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-Repeat
Interleaved
Codeword (64800b)
Interleaved
Codeword (64800b)
Interleaved
Codeword (64800b)
Codeword repeated Q times
11/11/2014

11. 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)
Channel State, FSN, etc. (640b)
Interleaved Codeword (64800b)
11/11/2014
1024-bit Header

12. 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
11/11/2014

13. 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
11/11/2014

14. Modulation
11/11/2014

15. 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)
48,000
U-311
311 (Max/4)
24,000
U-155
155.5 (Max/8)
11,200
U-51.8
51.8 (Max/24)
4,000
U-16 16 2
1216
U-8 8 4
608
U-4
288
U-2
128
11/11/2014

16. Wavelength Separate transmit, receive, acquisition wavelengths
Selected from ITU-T G.694.1, v.2.0 ( )
50-Ghz spacing, fixed grid
Optical C-band ( 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
11/11/2014

17. Relay Link Example
User Platform
Optical relay serves as a transparent link-layer bridge between User Platform and Ground Relay
Application
Transport
Ground Network
Ground Relay
Network
Network
Transparent Bridge
Link
Link
User Terminal
LAN
HDLC
Relay Platform
HDLC
Switch
FEC/ILV/ Q-Repeat
FEC/DeILV/ De-Q-Rep.
Relay Terminal 1
Relay Terminal 2
Phy Frame
Phy Frame
Phy Frame
Phy Frame
Random
De-Random
Random
De-Random
Modulation
De-Mod
Modulation
De-Mod
11/11/2014
Physical Link
Physical Link