Safety evaluation of digital post-release environment sensor data interface for distributed fuzing systems

Transcription

1 Safety evaluation of digital ost-release environment sensor data interface for distributed fuzing systems 57 th Fuze Conference, Newark, NJ Wednesday, July 30 th, 2014 Oen Session IIIA, 3:20 PM S. Ebenhöch, C. Schoe, Dr. I. Häring Funded by Federal Office of Bundeswehr Equiment, Information Technology and In-Service Suort (BAAINBw K 1.3) Contact: Stefan.Ebenhoech@emi.fraunhofer.de Fraunhofer EMI

2 Safety evaluation of digital ost-release environment sensor data interface for distributed fuzing systems: Content of resentation Motivation Post-release environment sensor (PRES) interface Simulation tool Safety evaluation results Conclusion Fraunhofer EMI 2

3 Motivation: Distributed fuzing systems Flexibility in geometry Comatibility of different fuzing, sensor weaon systems Distributed modular fuzing system* and Imroved relaceability of comonents Scalability of system erformance Simler realization of redundancy and searation of safety functions satial Alication of digital non-rorietary standard interfaces *NATO Indusrial Advisory Grou (NIAG): Study Grou (SG) 117, Future Fuzing Safety and Arming Technologies and Imlifications, Fraunhofer EMI 3

4 Motivation: Standard SAE AS5716A Current situation: mainly analog interfaces in airborne fuzing systems SAE AS5716A: Standard Electrical and Logical Interface for Airborne Fuzing Systems Addresses weaons using MIL-STD 1760 New revision: Pure digital data interface between sensor for detection of arming environment and fuzing system * Fuzing System Post release environment sensor Data evaluation Receiver Transmission Line Transmitter Data rocessing Signal rocessing Sensor element SAE AS5716A Goal: Evaluation of safety level - Is the new digital data transmission at least as safe as the established analog transmission in airborne fuzing systems? *Frank Robbins, Presentation: Fuzes for Air Force Unguided and Precision Guided Weaons, 2001: held at 45th NDIA Fuze Conference. Fraunhofer EMI 4

5 PRES-Interface: Characteristics Class 3 interface Definition of electrical interface characteristics RS-422 standard Transmission rate: 38.4 kbs Simlex mode Classification of interfaces PRES-Interface only in class 3 Subclasses secify data tye of sensor (analog, digital) Definition of rotocol structure for serial data interface RS-422 transmission line Fraunhofer EMI 5

6 PRES-Interface: Protocol Every byte (service data unit, SDU) is added by start, sto and (even) arity bits Fraunhofer EMI 6

7 PRES-Interface: Checksum Checksum algorithm:»when each data word (including the checksum word) of a message is rotated right cyclically by a number of bits equal to the number of receding data words in the message, and all the resultant rotated data words are summed using modulo 2 arithmetic to each bit (no carries), the sum shall be zero.«parity bits Word = 2 SDUs b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b c c c c c c c c c c c c c c c c 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 1,0 1,1 1,2 1,3 1,4 1,5 1,6 1,7 2,0 2,1 2,2 2,3 2,4 2,5 2,6 2,7 3,0 3,1 3,2 3,3 3,4 3,5 3,6 3,7 4,0 4,1 4,2 4,3 4,4 4,5 4,6 4,7 5,0 5,1 5,2 5,3 5,4 5,5 5,6 5,7 b6,0 b6,1 b6,2 b6,3 b6,4 b6,5 b6,6 b6,7 b7,0 b7,1 b7,2 b7,3 b7,4 b7,5 b7,6 b7,7 8,0 8,1 8,2 8,3 8,4 8,5 8,6 8,7 9,0 9,1 9,2 9,3 9,4 9,5 9,6 9,7 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 1,0 1,1 1,2 1,3 1,4 1,5 1,6 1,7 Checksum PRES Subclass Enumerator PRES Sign-of-Life PRES Data Tye PRES Data-1st byte PRES Data-2nd byte PRES Data-3rd byte PRES Data -4th byte PRES Data 5th byte PRES Data -6th byte PRES Data-7th byte Fraunhofer EMI 7

8 PRES-Interface: Checksum Checksum algorithm:»when each data word (including the checksum word) of a message is rotated right cyclically by a number of bits equal to the number of receding data words in the message, and all the resultant rotated data words are summed using modulo 2 arithmetic to each bit (no carries), the sum shall be zero.«b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b c c c c c c c c c c c c c c c c 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 1,0 1,1 1,2 1,3 1,4 1,5 1,6 1,7 3,7 2,0 2,1 2,2 2,3 2,4 2,5 2,6 2,7 3,0 3,1 3,2 3,3 3,4 3,5 3,6 5,6 5,7 4,0 4,1 4,2 4,3 4,4 4,5 4,6 4,7 5,0 5,1 5,2 5,3 5,4 5,5 b7,5 b7,6 b7,7 b6,0 b6,1 b6,2 b6,3 b6,4 b6,5 b6,6 b6,7 b7,0 b7,1 b7,2 b7,3 b7,4 Progressive rotation Word = 2 SDUs 9,4 9,5 9,6 9,7 8,0 8,1 8,2 8,3 8,4 8,5 8,6 8,7 9,0 9,1 9,2 9,3 1,3 1,4 1,5 1,6 1,7 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 1,0 1,1 1,2 Checksum 16 sums of 6 bits each for calculation of checksum bits PRES Subclass Enumerator PRES Sign-of-Life ( b b b b b b b b ) mod 2 0 i,0 i,1 i,2 i,3 i,4 i,5 i,6 i,7 i Parity bits b1,0 b2,7 b4,6 b6,5 b8,4 c0,3 mod 2 0 PRES Data Tye PRES Data-1st byte PRES Data-2nd byte PRES Data-3rd byte 12 sums of 9 bits each for calculation of arity bits PRES Data -4th byte PRES Data 5th byte PRES Data -6th byte PRES Data-7th byte Fraunhofer EMI 8

9 Start Bit LSB B0 B1 B2 B3 B4 B5 B6 MSB B7 Parity Bit Sto Bit Start Bit LSB B0 B1 B2 B3 B4 B5 B6 MSB B7 Parity Bit Sto Bit Simulation tool: Architecture MIL-STD Data UB Word (N = 1 is first word) LB AS5716 Bit Transmission Develoment of flexible simulation latform for the analysis of various rotocol structures Examle [0142h] Time PRES Generation PRES Message SDU 1 SDU 2 SDU 3 SDU 4 Calculation of checksum SDU 5 SDU 6 SDU 7 SDU 8 Calculation of arity bits SDU 9 SDU 10 CSB 1 CSB 2 CSB 2 CSB 1 SDU 10 SDU 2 SDU 1 Transmission line Injection of bit flis in message Imlementation of error models... = Syncro Fuzing System = Start b Verification PRES Message SDU 1 SDU 2 SDU 3 SDU 4 Verification checksum SDU 5 SDU 6 SDU 7 SDU 8 Checking arity bits SDU 9 SDU 10 = Sto b = Parity CSB 1 CSB 2 = CSB 1 Fraunhofer EMI 9

10 Simulation tool: Error modeling Random errors Model: Binary symmetric channel Transmitted bit is flied with the robability Burst errors Secific burst model with several Dynamic variation of model in simulation arameters arameters Couled simulation (combination of rotocol and circuit level): Circuit model of transmission line Electrical modeling of interferences (e.g. lightning) Bits Length frame / message Burst region Bitflis Proability of bitflis in burst region Generation PRES Message Schematic of transmission line Verification PRES Message Fraunhofer EMI 10

11 Simulation tool: Mathematical validation Assuming that bit flis occur indeendently with robability Using binomial distributions we find the following robabilities for n words For not detecting bit flis using checksum only: 16 n / 2 n CSA unrecognised 2i ( n2i) n 16n P ( ) ( 1) ( 1 ) ( 1 ) i 1 2i For not detecting (actual) bit flis using arity bits only: 12 PB unrecognized 4 ( ) 9 2 i 9 2 ( i 9 ( ) n P ). i 0 2i Combinatorial considerations yield that there have to be at least four bit flis so that CSA as well as PB do not detect defectiveness of message Mathematical transformation of resented rogressive rotation P Four bitflis undetected ( ) 2 min n ( i ) ( 8 n1 8 n1 ( n 1 ) ( i j ) 4 18n 4 { i, 1 j} 8 k 1 ) i 0 j 0 i 0 j 0 k 0 Fraunhofer EMI 11

12 Safety evaluation results: Random errors Simulation of messages for every bit fli robability Good match between simulation and combinatorial consideration (for small ) For high bit fli robabilities checksum and arity bits mechanisms are CSA unrecognised robabilistically indeendent ( * ) P P PB unrecognized Malfunction of safety mechanisms (combinatorial aroach - 4 bit fli errors) Malfunction of safety mechanisms (assumtion of robabilistically indeendence) Simulation results Probability of bit fli 10-3 Probability of undetected erroneous message 10-9 Fraunhofer EMI 12

13 Safety evaluation results: Burst errors Burst error model Simulation of messages Variation of model arameters No undetected erroneous messages Electrical modeling of interferences Electrical modeling of interferences Performance of couled simulation Modeling interferences according to MIL-STD 464 (Electromagnetic environmental effects) No undetected erroneous messages Transmitter Effects on rotocol level Receiver Future work Evaluation of data transmission reliability in laboratory exeriments Fraunhofer EMI 13

14 Conclusion Digital data transmission: Minor sensitivity to electrical interferences High efficiency of mechanisms for error detection (check sum and arity bits) Random errors: For common bit fli rates, robability of undetected erroneous message less than 10-9 Burst errors: Accetable safety levels achieved by first analyses, no undetected erroneous messages Fraunhofer EMI has an efficient simulation latform for safety and reliability analysis of digital data transmission (analysis on circuit and rotocol level) Fraunhofer EMI 14

15 Conclusion Further (ossible) safety features of PRES-interface to revent unintentional arming For fuzing activities several messages in sequence have to reresent the same value Plausibility checks of fuzing system could identify erroneous sensor data (for some SDUs only a few valid states are ossible) Checking comatibility between sensor and fuzing system (correct class & subclass) Detection of illegal transmission sequences (sign-of-life & start/sto bits) New interface offers better set-u between PRES, fuzing system and weaon for secific safety criteria Usage of digital PRES-Interface would rovide a considerably imroved transmission reliability and therefore safety in most of the standard relevant alications. PRES-Interface could be an imortant element for future distributed systems Fraunhofer EMI 15

16 Thank you for attention! Questions? Stefan Ebenhöch Grou Leader System Reliability Safety Technology and Protective Structures Fraunhofer EMI Am Klingelberg Efringen-Kirchen Germany Tel.: / Stefan.Ebenhoech@emi.fraunhofer.de Fraunhofer EMI 16