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Increased mobility coupled with a possible reduction of cabling costs and deployment time makes wireless communication an attractive alternative for the automation industry and related application areas. Methods compensating for the high probability of bit errors accompanying wireless transmissions are, however, needed. This is predominantly important in industrial applications with strict reliability and timing requirements, which cannot be met by standard communication protocols as, e.g., TCP. In this paper, a way of combining retransmissions with real-time worst-case scheduling analysis is presented that can offer both a high grade of reliability and hard real-time support. The presented solution handles one or several retransmission attempts of erroneous data without jeopardizing already guaranteed delay bounds of other packets. A real-time analysis for a full-duplex, asymmetric link, utilizing the novel retransmission scheme and supporting both piggybacked and nonpiggybacked acknowledgments, is provided. A simulation study is presented that evaluates the performance of the retransmission scheme for bit-error rates typically experienced in wireless communication. The results clearly indicate a possible reduction of the message error rate by several orders of magnitude.
Date of Publication: Nov. 2009