High Data Throughput Recommended Standard

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

2. User Segment Relay Segment B/A B/A A A A A Space Relay Architecture 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

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

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

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

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

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

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 302 307 • Excellent power efficiency BCH LDPC 32,208 source bits 32,400 code bits 64,800 code bits

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 • Convolultionalinterleaver requires ½ memory of equivalent performance block interleaver

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. 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) 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

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

14. Modulation

15. Summary of Data Rate Modes

16. 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

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 Relay Platform HDLC 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 Physical Link Physical Link