Channel Coding versus Cooperative ARQ: Reducing Outage Probability in Ultra-Low Latency Wireless Communications

Abstract

Abstract-Nowadays wireless communications still lack the ability to provide high reliability and low latency, although mission-critical applications, such as found in industrial automation, rely on both requirements. The main challenge is that an improved reliability often comes at the price of an increased latency. It has been shown that cooperative schemes can effectively increase the reliability by leveraging spatial diversity. However, an important question remains how to integrate cooperative schemes when dealing with very short latency bounds and especially how much time should be reserved for potential retransmissions. In this work, we propose and evaluate a centralized communication system that uses cooperative ARQ to achieve high reliability under the constraint of a strict latency bound of 1 ms. We evaluate this system analytically, using an outage-capacity model with average channel state information, by varying the reserved time for retransmissions, where a shorter time for retransmissions allows to apply stronger channel codes in the original transmission. As a baseline, we use a system without cooperation mechanism, thus applying the given time for stronger channel codes in the direct transmission of a message. In case of cooperation, a third station may act as a relay if the original transmission failed. Our results reveal that an optimal size of the reserved retransmission time exists around 15% to 30% of the total frame time, increasing the reliability by several orders of magnitude, even for a large number of transmissions within a communication cycle.

Performance analysis of cooperative ARQ systems for wireless industrial networks

“…The considered system model is based on the one presented in [5]. In the following, we focus on the extensions C-RELAYS and D-RELAYS, as well as the derivation of their performance.…”

“…In D-RELAYS, we apply the frame structure of [5], including a Transmission Phase (TP) and a Retransmission Phase (RP). In the TP, N equal time slots of length T t are reserved for direct transmissions between stations.…”

“…The AP specifies the RP length upfront, not knowing how many transmissions will fail during the TP. This yields the definition of the single link outage probability [5]:…”

“…Yet, there is a lack of performance evaluations of systems supporting multi-user transmission frames with cooperative ARQ. In a previous work [5], we investigated a Time Division Multiple Access (TDMA) system incorporating cooperative ARQ, where transmissions and retransmissions are centrally scheduled by the Access Point (AP). Although we showed that multi-user cooperative ARQ can be effectively combined with a strict time limit, further mechanisms need to be considered to achieve the anticipated reliability.…”

“…Although we showed that multi-user cooperative ARQ can be effectively combined with a strict time limit, further mechanisms need to be considered to achieve the anticipated reliability. Therefore, in this paper, we extend our analysis in [5] by considering two more sophisticated designs and analytically determining their performance: C-RELAYS A centralized system that implements cooperative ARQ with perfect Channel State Information (CSI) using multiple transmit/receive antennas at the AP. As a result, the AP adapts slot lengths and schedules transmissions either directly between stations or indirectly via its multiple antennas, depending on the observed link qualities.…”