1. Application of Data Compression to the MIL-STD-1553 Data Bus Scholar’s Day Feb. 1, 2008 By Bernard Lam

2. Overview Background Background MIL-STD-1553 MIL-STD-1553 Bus Trace Analysis Bus Trace Analysis Solutions – Compression Algorithms Solutions – Compression Algorithms Zero-Tracking, Modified Run-Length, and Differential Zero-Tracking, Modified Run-Length, and Differential Error Analysis Error Analysis Conclusions & Future Research Conclusions & Future Research

3. Goal Of Research To extend the bandwidth capabilities of MIL- STD-1553 Bus, using compression techniques. To extend the bandwidth capabilities of MIL- STD-1553 Bus, using compression techniques. Develop algorithms suitable for legacy systems Develop algorithms suitable for legacy systems Demonstrate that the time to compress and decompress data is offset by the overall savings in data transmission time. Demonstrate that the time to compress and decompress data is offset by the overall savings in data transmission time.

4. Timing Analysis Timing Diagram

5. Background ~ MIL-STD-1553 MIL-STD-1553 serial data bus MIL-STD-1553 serial data bus Developed in the late 1960’s and early 1970’s Developed in the late 1960’s and early 1970’s Limited/Low Bandwidth Limited/Low Bandwidth 1 Mb/s 1 Mb/s Has lead to development of multiple independent busses Has lead to development of multiple independent busses Time division multiple (TDM) access Time division multiple (TDM) access System Model

6. Background ~ MIL-STD-1553 MIL-STD-1553 (cont’d) MIL-STD-1553 (cont’d) Manchester Bi-phase encoding Manchester Bi-phase encoding Data word size: 16 bit Data word size: 16 bit Sync Waveform Sync Waveform Parity Bit Parity Bit Message Format

7. Background ~ MIL-STD-1553 MIL-STD-1553 (cont’d) MIL-STD-1553 (cont’d) Max. single-command transmission size of 32 words Max. single-command transmission size of 32 words Safety and Mission Critical System Safety and Mission Critical System Real-Time System Real-Time System Replacement of MIL-STD-1553 with updated bus protocol, such as Fibre Channel, not a viable solution because of extensive costs. Replacement of MIL-STD-1553 with updated bus protocol, such as Fibre Channel, not a viable solution because of extensive costs.

8. Bus Trace Analysis Analysis was conducted using data from multiple bus traces of data captured at the F/A – 18 Advanced Weapons Laboratory. Analysis was conducted using data from multiple bus traces of data captured at the F/A – 18 Advanced Weapons Laboratory. Each trace represented roughly 30 seconds of flight data and included examples of mode changes and start-up conditions. Each trace represented roughly 30 seconds of flight data and included examples of mode changes and start-up conditions.

9. 73.5%88.8%68%Avg. % Zeros 72.0%88.5%53.5%Min % Zeros 78.6%90.1%96.3%Max % Zeros 5 Hz10 Hz20 Hz Bus Trace Analysis Percent of Zeros  Significant amount of zeros

10. 3.3% 3.9%Avg. % Changes 2%0%2.0%Min % Changes 78.6%27.5%21.7%Max % Changes 5 Hz10 Hz20 Hz Bus Trace Analysis Percent of Changes  Limited number of changes between consecutive message transmissions

11. Data Compression Lossless vs. Lossy Compression Lossless vs. Lossy Compression Lossless Lossless Original data is completely retrievable by means of decompression Original data is completely retrievable by means of decompression Ex. Winzip, GIF Ex. Winzip, GIF Lossy Lossy Lose information; original data not retrievable when decompressed Lose information; original data not retrievable when decompressed Higher Compression Ratios Higher Compression Ratios E.g., jpeg, mpeg, mp3 E.g., jpeg, mpeg, mp3

12. Coding Performance and Efficiency Coding Performance and Efficiency Measured by compression ratio Measured by compression ratio Data Compression AFC1 FFFF compress decompress AFC1 FFFF yyyy xxxx

13. Data Compression Criteria Criteria Lossless Compression Lossless Compression Take advantage of message format of MIL-STD- 1553 Take advantage of message format of MIL-STD- 1553 Limit worst case expansion Limit worst case expansion Limit computational and memory requirements Limit computational and memory requirements

14. Compression Algorithms Common Value Tracking Common Value Tracking Zero-Tracking Zero-Tracking Modified Run-Length Encoding Modified Run-Length Encoding Differential Encoding Differential Encoding

15. Zero Tracking Encodes long sequences containing mostly zeros Encodes long sequences containing mostly zeros Uses marker sequence to indicate the position of zeros Uses marker sequence to indicate the position of zeros Transmits Transmits Position Address (marker sequence) Position Address (marker sequence) Non-Zero Data Words Non-Zero Data Words

16. Zero-Tracking Encoding (Example) 486A 09 08 0B 07 06 AC9F5 48604 AC9F593 59FFFF2 FFFF01 CBD0CBD0CBD0CBD000 Encoded Data (Hex) ZT Input Data (Hex) Word Count (Hex) 0 0 1 1 1 0 1 1 1 1 01 Bit Position Word

17. Zero Tracking If a 32-word block is compressed If a 32-word block is compressed 2 data words are required to indicate positions 2 data words are required to indicate positions Can transmit maximum of 31 uncompressed data words Can transmit maximum of 31 uncompressed data words Most significant bit in 1st address word is used to indicate if uncompress/compressed Most significant bit in 1st address word is used to indicate if uncompress/compressed Worst Case Compression Ratio Worst Case Compression Ratio comp. ratio = 31/32 comp. ratio = 31/32

18. Modified Run-Length Encoding Encodes consecutive sequences of identical words Encodes consecutive sequences of identical words Uses marker sequence to indicate the presence of repeated sequences within block set Uses marker sequence to indicate the presence of repeated sequences within block set For block of 32 words For block of 32 words Worst Case Expansion – 31/32 Worst Case Expansion – 31/32

19. Modified Run-Length (Example) 9840A 98409 56048 B1F4B 56047 56046 B1F456045 984056044 5604FFFF3 FFFF02 001 67A0 00 Encoded Data (Hex) RT Input Data (Hex) Word Count (Hex) 0 1 1 0 0 1 0 1 1 1 1 0 Bit Position Word

20. Differential Encoding Encodes only changes of previous vs. current word locations Encodes only changes of previous vs. current word locations A differential scheme takes advantage of the fact that for a given rate group one transmission to the next does not change A differential scheme takes advantage of the fact that for a given rate group one transmission to the next does not change Two buffers are required for comparison of previous and current transmissions Two buffers are required for comparison of previous and current transmissions

21. Differential Encoding 1A14F0052B 089668966A 1FDA989669 19FB222228 0FFFFFFFF7 0FFFFFFFF6 0654265425 A14F0000000004 FDA90000000003 9FB2112F8AF582 12F80081508151 20D020D020D020D00005400540 Encoded Data (Hex) DT Current Data (Hex) Previous Data (Hex) Word Count (Hex) Bit Position Word

22. 1.318.377.2214.475.7412.47Differential 1.172.132.802.441.971.34 Mod. Run-Length 2.602.443.394.651.662.63Zero-Tracking MC2MC1MC2MC1MC2MC1 5 Hz10 Hz20 Hz Compression Ratios Average Compression Ratios For Algorithms

23. Compression Bit Status 0 15 bits 16 bits 16 bits 30 Data Words 1 15 bits 31 Data Words Block Set Format Compression Status 30 – 16 bit Data Words Bit Position Word 31 – 16 bit Data Words 1st Bit of 1st 16-bit word indicates the compression status ‘1’ - equals uncompressed ‘0’ – equals compressed

24. Transmission Error Effects Effects of data errors can be amplified when using data compression Effects of data errors can be amplified when using data compression If higher levels of error detection and correction (EDAC) are needed, one or more data words can be dedicated to EDAC If higher levels of error detection and correction (EDAC) are needed, one or more data words can be dedicated to EDAC

25. Transmission Error Effects Standard 1553 Error Checking Standard 1553 Error Checking Bit Errors can be detected Bit Errors can be detected Exception – multiple-bit errors without parity change cannot be detected Exception – multiple-bit errors without parity change cannot be detected Common Value Tracking Common Value Tracking If an undetected error is in the bit position word, multiple words can be corrupted. If an undetected error is in the bit position word, multiple words can be corrupted. If an undetected error is in the data word, only that word location is impacted If an undetected error is in the data word, only that word location is impacted

26. Transmission Error Effects Modified Run-Length Compression Modified Run-Length Compression Like zero tracking a error in the bit position word can invalidate a run Like zero tracking a error in the bit position word can invalidate a run Error dramatically worse result than that of zero- tracking Error dramatically worse result than that of zero- tracking Differential Encoding Differential Encoding Error in address word can result incorrect updating Error in address word can result incorrect updating Worst Case – All data words are updated Worst Case – All data words are updated Further Research Required Further Research Required

27. Future Research Error Handling Routines Error Handling Routines Effects of mode-changing and start-up Effects of mode-changing and start-up Timing analysis for Run-Length and Differential Encoding Timing analysis for Run-Length and Differential Encoding

28. Conclusions Reviewed Statistical Analysis of Trace Data Reviewed Statistical Analysis of Trace Data Able to achieve compression ratios greater than one for all algorithms Able to achieve compression ratios greater than one for all algorithms Discussed Error Analysis Discussed Error Analysis Preliminary timing simulations of timing look promising Preliminary timing simulations of timing look promising

29. Acknowledgements Dr. Russell Duren Dr. Russell Duren Dr. Michael Thompson Dr. Michael Thompson

30. QUESTIONS?