Emerging industrial applications reqUiring reliable wireless real-time communications are numerous. Using existing standards such as IEEE 802.15.4 is essential for reasons of interoperability and cost efficiency. However, since 802.15.4 is unable to provide predictable channel access, real-time guarantees cannot be given. Further, the noisy wireless channel makes reliable communica tions particularly challenging. By adding a deterministic medium access method and a transport protocol with a truncated retransmission scheme to 802.15.4, we jointly eriforce reliability and predictability. We evaluate our solution analytically by real-time schedulability analysis including retransmissions, and by computer simulations. We show that the message error rate can be improved by several orders of magnitude while keeping the utilization penalty at reasonable levels.
Abstract-This paper presents a framework for how to use ARQ (Automatic Repeat Request) in combination with real-time worstcase scheduling analysis to be able to support reliable hard realtime communication. We show how to handle retransmissions of erroneous data packets, while still not jeopardizing stated delay guarantees of other packets. We demonstrate this by taking a point-to-point link as an example. Through our simulation studies we have shown that a reduction of the message error rate by several orders of magnitude is possible with a reasonable utilization penalty.
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