A general framework for the deterministic medium access on the Controller Area Network

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2022-6-13
Akpınar, Murat
This thesis proposes a general framework CANDS (Controller Area Network with Determinism and Synchronization support) for in-vehicle communication on CAN. CANDS features a hierarchy of novel clock synchronization (CS) algorithms with different levels of clock accuracy and implementation complexity. Moreover, CANDS realizes our original idea of weak time division multiple access (WTDMA) for deterministic bus access, while being fully compatible with the standard CAN protocol and its recent extensions. CS methods within CANDS apply offset and drift correction. While offset correction is performed based on timestamps in periodic reference messages (RMs), drift correction is realized based on (1) the re-synchronization mechanism of the CAN bit timing; (2) drift estimates computed from periodic timestamps with RMs and (3) drift estimates determined in a discrete-time feedback control loop. Since accurate timestamps are essential for the CS performance, the thesis further develops a new timestamping (TS) method, which reduces the effect of uncertainties that are caused by the CAN bit timing, oscillator drifts and different cable lengths. Overall, clock accuracies below 100ns are achieved in hardware experiments with our TS method and CS algorithms. Benefiting from the achieved clock accuracy levels, the thesis next introduces WTDMA as a new method for slotted medium access on CAN together with novel message scheduling algorithms for the assignment of time slots in WTDMA. WTDMA is realized in software and a certain degree of interference between adjacent time slots is tolerated with the usage of Carrier Sense Multiple Access/Collision Resolution (CSMA/CR) and the non-preemptive message transmission on CAN. Sufficient conditions for the correct operation of WTDMA are derived and its practicability is validated with comprehensive hardware experiments. Specifically, bus loads above 90% and deterministic message latencies in the order of hundreds of microseconds are achieved.

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Citation Formats
M. Akpınar, “A general framework for the deterministic medium access on the Controller Area Network,” Ph.D. - Doctoral Program, Middle East Technical University, 2022.