Meeting reliability and real-time demands in wireless industrial communication

Wired and Wireless Reliable Real-Time Communication in Industrial Systems

“…A RT channel is an abstraction of a traffic flow over a link or a network, where resources have been allocated to guarantee a certain minimum throughput and a bounded end-to-end delay. The basic parameters of a network layer RT channel i, following the notation in (Jonsson & Kunert, 2008b) (we follow this notation in the whole chapter), are the period (or minimum interarrival time), P N,i , the maximum message length in bits each period, L N,i , and the end-to-end delay bound, D N,i , where N denotes the network layer. A RT channel can then be defined as…”

Towards Reliable Wireless Industrial Communication With Real-Time Guarantees

“…Therefore, we set (17) In order to derive the delay bound for ordinary transmissions, (1) is rephrased as (18) As for the ordinary transmission, the new deadline of each retransmission, i.e., the isolated maximum queueing delay can be calculated by subtracting all other delays from the delay bound (further elaborated on at a later point in this paper) (19) where (20) The last possible retransmission has no ACK answer which results in fewer delay components. In (20), is included as the maximum blocking time introduced by a packet with a longer deadline (thereby actually having a lower priority), as its nonpreemptive transmission already might have been initiated. Additionally, is deducted twice for each, but the last, retransmission attempt.…”

“…Regarding the retransmission channels, (20) has to be adapted the same way as (12), affecting the result of (19). Equation (20) is therefore rewritten as (30) The delay bound for each retransmission attempt except the last one, originally calculated in (22), to be used in the runtime implementation for timeout calculations, is given by (31) Further adaptation is needed in the utilization check [(23)] by adding the needed additional network capacity for ACK packets (32) Also, the workload function [ (24)] is extended with a term for the ACK packets (33) where if is true, otherwise, zero.…”

“…In this paper, partly based on earlier conference papers [19], [20], a complete framework for a full-duplex, asymmetric link is presented. The framework supports a certain number of retransmissions when needed, including several retransmission attempts, to support wireless industrial real-time communication.…”

“…Based on earlier results, both timing analysis and real-time scheduling analysis have been developed for the new framework, still based on the earliest deadline first (EDF) scheduling policy [21]. Compared to [19] and [20], this paper no longer assumes a dedicated physical channel for ACK, and the asymmetry of the wireless medium has been taken into consideration, no longer assuming equal bit rates in each direction, which has led to incremental, but highly significant changes in the framework. Additionally, an analysis of both piggybacked and nonpiggybacked ACKs is provided.…”