Performance Analysis of Hybrid ARQ for Ultra-Reliable Low Latency Communications

Abstract

Considering an ultra-reliable low latency communication scenario, we assess the trade-off in terms of energy consumption between achieving time diversity through retransmissions and having to communicate at a higher rate due to latency constraints. Our analysis considers Nakagami-m blockfading channels with Chase combining hybrid automatic repeat request. We derive a fixed-point equation to determine the best number of allowed transmission attempts considering the maximum possible energy spent, which yields insights into the system behavior. Furthermore, we compare the energy consumption of the proposed approach against direct transmission with frequency diversity. Results show substantial energy savings using retransmissions when selecting the maximum number of transmission attempts according to our approach. For instance, considering a Rayleigh channel and smart grid teleprotection applications, our approach uses around 8 times less energy per bit compared with a direct transmission with frequency diversity.

Hybrid ARQ in Wireless Packetized Predictive Control

“…The first step to evaluate the energy savings of the proposed method is using (12) to calculate the required power ir to meet the control outage probability after cha channel uses. We can observe that ir > ★ in (12) since cha < max .…”

“…However, HARQ must be carefully designed when latency constraints must be met. In this regard, the work in [12] evaluates the performance of HARQ under latency constraints, where the retransmissions are replicas of the original transmissions and are combined at the receiver, in a scenario representative of smart grid teleprotection applications. Results show significant energy savings, however, the focus of [12] is not the case of WNCS, and therefore there is no communication-control co-design.…”

“…In this regard, the work in [12] evaluates the performance of HARQ under latency constraints, where the retransmissions are replicas of the original transmissions and are combined at the receiver, in a scenario representative of smart grid teleprotection applications. Results show significant energy savings, however, the focus of [12] is not the case of WNCS, and therefore there is no communication-control co-design. In this paper, we aim at minimizing the wireless resources consumption of a WNCS making use of PPC, as in [6], but considering the application of incremental redundancy HARQ.…”

On the Multiplexing of Data and Metadata for Ultra-Reliable Low-Latency Communications in 5G

“…[53]- [57]). Interesting power allocation ideas are proposed to minimize the energy consumption of Chase-Combining HARQ (CC-HARQ) for Rayleigh and Nakagami-m blockfading channels in [53] and [54], respectively. On the other hand, resource allocation schemes for incremental redundancy HARQ (IR-HARQ) are discussed in [55], [56].…”

“…Two retransmission protocols of IR-HARQ and CC-HARQ are considered. Using CC-HARQ, the same codeword as the initial transmission is sent over the retransmission round [54]. The UE combines multiples of received data packets using maximum ratio combining (MRC) to enhance the desired signal power and increase successful decoding probability.…”