Application of hybrid ARQ to controller area networks
Krishna Chaitanya Emani · 2007
This thesis proposes two types of Hybrid Automatic Repeat reQuest (HARQ) schemes for the Controller Area Network (CAN) to combat Electro-Magnetic Interference (EMI) and improve network efficiency. The proposed HARQ schemes encode the original CAN data frames by a Reed-Solomon (R-S) code so that burst errors due to EMI may be corrected at the receive nodes. Therefore, the probability of error frames is reduced, thereby reducing the probability of retransmission. Hence, the network efficiency of the system is improved. HARQ Type-I employs a 20-bit R-S code to encode the CAN frame and transmits the R-S code along with the CAN frame. A variant of HARQ Type-I is also studied, which replaces the error-detection code, Cyclic Redundancy Check (CRC) in the original CAN frame by an error-correction cyclic code. HARQ Type-II either uses a 20-bit R-S code alone or a combination of 20-bit and 40-bit R-S codes. This method transmits the original CAN frame in normal conditions. Only when the receiver detects an error frame, it sends a negative acknowledgement (NACK) and the transmitter will send the parity bits of the error frames. Computer simulations show that the proposed HARQ schemes have several advantages over the conventional ARQ currently used in the CAN bus. First, the error-correction capability in HARQ schemes enables the receivers to correct random or burst errors when they are spread over 2 R-S symbols. The burst length can be of any length less than 11 bits. Second, the HARQ scheme reduces the probability of retransmission by 100% for burst lengths shorter than 7 bits. When the probability of burst error occurrence is 40%, the probability of retransmission is reduced by 30% for burst lengths of 8 bits and 11% for burst lengths of 10 bits. Third, the proposed HARQ schemes require minimal changes in the CAN frame structure or the communication protocol and are easy to implement in practical hardware.