Automatic Repeat Request Scheme Research Articles

Hybrid Duplex Medium Access Control Protocol for Tsunami Early Warning Systems in Underwater Networks

Tsunamis are devastating natural phenomena that cause extensive damage to both human life and infrastructure. To mitigate such impacts, tsunami early warning systems have been deployed globally. South Korea has also initiated a project to install a tsunami warning system to monitor its surrounding seas. To ensure reliable warning decisions, various types of data must be combined, but efficiently transmitting heterogeneous data poses a challenge due to the unique characteristics of underwater acoustic communication. Therefore, this paper proposes a Hybrid Duplex Medium Access Control (HDMAC) protocol designed for a tsunami warning system, with a specific focus on heterogeneous data transmission. HDMAC efficiently handles both seismic and environmental data by utilizing hybrid duplexing, which combines frequency duplex for seismic data with time duplex for environmental data. The protocol addresses the distinct transmission requirements for each data type by optimizing channel utilization through a group Automatic Repeat request (ARQ) scheme and packet size adjustment. Theoretical analysis predicts that HDMAC can achieve a channel utilization of up to 0.91 in smaller networks and 0.64 in larger networks. HDMAC is validated through simulations, and the simulation results closely match these predictions. The simulation results demonstrate the efficiency of HDMAC in supporting real-time submarine earthquake monitoring systems.

An Adaptive Hybrid Automatic Repeat Request (A-HARQ) Scheme Based on Reinforcement Learning

V2X communication is susceptible to attenuation and fading caused by external interference. This interference often leads to bit error and poor quality and stability of the wireless link, and it can easily disrupt packet transmission. In order to enhance communication reliability, the 3rd Generation Partnership Project (3GPP) introduced the Hybrid Automatic Repeat Request (HARQ) technology for both 4G and 5G systems. Nevertheless, it can be improved for poor communication conditions (e.g., heavy traffic flow, long-distance transmission), especially in advanced or cooperative driving scenarios. In this paper, we propose an Adaptive Hybrid Automatic Repeat Request (A-HARQ) scheme that can reduce the average block error rate, the average number of retransmissions, and the round-trip time (RTT). It adapts the Q-learning model to select the timing and frequency of retransmission to enhance the transmission reliability. We also design some transmission schemes—K-repetition, T-delay and [T, K]-overlap—which are used to shorten latency and avoid packet collision. Compared with the conventional 5G HARQ, our simulation results show that the proposed A-HARQ scheme decreases the system’s average BLER, the number of retransmissions, and the RTT to 5.55%, 1.55 ms, and 0.97 ms, respectively.

Raptor-like Coded Broadcasting for Efficient V2X Communications

Broadcasting is a critical feature in V2X communication, allowing for the simultaneous dissemination of safety-critical messages to all nearby vehicles. However, the requirement for low latency in information dissemination and the need for reliable and efficient data transmission pose significant challenges to broadcasting in V2X communication systems. In this paper, we present a novel raptor-like coded broadcasting (RLCB) scheme for low-latency V2X communications. Firstly, we introduce feedback into a concatenated fountain code, and adjust its precoding and coding structure to achieve effective data deliverance under a limited number of retransmissions for low-latency transmission. Then, based on the raptor-like encoding and decoding structure, we propose a mutual exclusion-based network encoding (MENC) algorithm to enable retransmission in broadcasting scenarios. We also conduct a complexity analysis on the encoding and decoding process of our proposed scheme. Numerical results demonstrate the superior performance of our proposed scheme in reducing the packet error rate (PER) and improving spectral efficiency compared to the R10 code and hybrid automatic repeat request (HARQ) scheme.

Age of Information in Physical-Layer Network Coding Enabled Two-Way Relay Networks

This paper investigates information freshness of two-way relay networks (TWRNs) operated with physical-layer network coding (PNC). Information freshness is quantified by age of information (AoI), defined as the time elapsed since the generation time of the latest received information update. PNC reduces communication latency of TWRNs by turning superimposed electromagnetic waves into network-coded messages so that end users can send update packets to each other more frequently via the relay. While sending update packets more frequently has the potential to reduce AoI, how to handle packet corruption has not been investigated. Specifically, if an old packet is corrupted in any hop of a TWRN, one needs to decide whether to drop or to retransmit the old packet. Therefore, we study the average AoI with and without automatic repeat request (ARQ) in PNC-enabled TWRNs. Interestingly, our analysis shows that neither the non-ARQ scheme nor the pure ARQ scheme achieves a good average AoI. Hence, we put forth an uplink-lost-then-drop (ULTD) protocol that combines packet drop and ARQ. Experiments on software-defined radios indicate that ULTD significantly outperforms non-ARQ and pure ARQ schemes in terms of average AoI, especially when the two end users have imbalanced channel conditions. We believe the insight of ULTD on TWRNs generally applies to other two-hop networks.

Theoretical modeling and analysis of Uplink performance for Three-dimension spatial RISs-aided Wireless communication systems

Reconfigurable intelligent surface (RIS) has emerged as a crucial technology capable of improving the performance of future wireless communication (WC) systems. Although a significant body of studies has investigated into the performance analysis of RIS-aided WC systems, most of them fail to consider the impact of multiple RISs on WC systems. Particularly, the influence of RISs randomly distributed in 3-D (three dimension) space is still an open issue. Furthermore, how phase shift error and ARQ (automatic repeat request) scheme affect the transmission behavior of RIS-aided WC systems should also be taken into account. In light of the above limitations, we propose a novel theoretical model to analyze the uplink transmission performance of 3-D spatial RISs-aided WC systems. In the modeling process, we firstly provide an end-to-end (E2E) channel model using a single RIS, where the RIS enables optimal phase shift control. Next we construct a 3-D spatial uplink transmission model, where the multiple RISs are spatially distributed as a homogeneous 3-D PPP (Poisson point process). The impacts of multiple factors including the selection of RISs, buffer size of user, traffic rate and ARQ scheme are comprehensively considered. With this, we derive the closed-form expressions of uplink transmission metrics. Moreover, we further extend the proposed theoretical model under imperfect phase shift control. Finally, we evaluate the uplink transmission performance of 3-D spatial RIS-aided WC systems, and validate the proposed theoretical model.

Average age upon decisions with truncated HARQ and optimization in the finite blocklength regime

We consider an update-and-decide IoT-based wireless network, where information packets generated from dual sources are co-stored in the transmitter’s buffer, while decisions are made at the destination. Two practical assumptions about the communications between the transmitter and destination are taken into account: the communications are operating with finite blocklength (FBL) codes, and truncated hybrid automatic repeat request (HARQ) schemes are exploited to improve the FBL reliability, i.e., the number of allowed rounds of (re)transmissions is finite. For the first time, this paper characterizes the timeliness of status updates, namely age upon decisions (AuD) (which highlights the timeliness of the information at decisions in comparison to the concept of age of information), for such truncated HARQ-assisted wireless network. First, we characterize the inter-arrival time between two adjacent successfully transmitted packets, while taking into consideration the preemption policy and the randomness of the number of preempted packets from the same source. In particular, the probability density function, statistical performance of such inter-arrival time are derived. Following these characterizations, we propose a new approach to determine the average AuD and obtain a closed-form expression accordingly. Subsequently, a joint blocklength and arrival rate optimization problem is considered to minimize the obtained average AuD. Before addressing the formulated problem, we prove the convexity of decoding error probability in CC-HARQ and IR-HARQ with respect to blocklength. Then, we prove the convexity of average AuD with respect to blocklength and arrival rate, respectively. By an efficient alternating algorithm, we obtain a efficient solution. Via simulations, we evaluate the performance and conclude a set of guidelines for designs on the considered network.

A new HARQ scheme for 5G systems via interleaved superposition retransmission

Within the framework of the 5G new radio (NR), we propose a new hybrid automatic repeat request (HARQ) scheme to improve the throughput performance. The difference between the proposed scheme and the conventional one lies in the first retransmission, where the erroneous coded block group is interleaved and superimposed (XORed) onto a fresh coded block group. At the receiver, an iterative message-passing decoding algorithm can be employed to recover the target erroneous code block group (CBG). Only when the superposed retransmission fails, the conventional incremental redundancy (IR) or repetition redundancy (RR) retransmission is initiated. In any case, since the first retransmission is along with but has negligible effect on the fresh CBG, it costs neither transmitted power nor bandwidth. Monte-Carlo simulation results reveal that the presented HARQ schemes can achieve throughput improvements up to 10% over block fading channels and up to 50% over fast fading channels in comparison with the original 5G CBG-level HARQ scheme but without excessively increasing the implementation complexity.

On the Buffer Size of Perfect RLNC in Full-Duplex Relay Networks

In the next-generation wireless networks, full-duplex, relaying, and random linear network coding (RLNC) are popular techniques to enhance the network performance such as efficiency and reliability. For full-duplex relay networks, a perfect RLNC scheme known as FBPF (Fewest Broadcast Packet First) was recently proposed and demonstrated a better throughput, or equivalently, expected completion delay performance than the Automatic Repeat Request scheme. However, the original FBPF scheme assumes unlimited buffer and does not take the buffer size into consideration. In this paper, we generalize the FBPF scheme to consider the buffer size as a new parameter. Based on a novel Markov chain model, explicit formulae to characterize the expected completion delay are deduced. Moreover, we present a criterion on the optimal selection of the buffer size under a quality of service constraint, so that the selected buffer size is significantly reduced while the completion delay performance is comparable to the original FBPF scheme with unlimited buffer.

Multiple decoding for polar-coded chase combining HARQ

The polar-coded hybrid automatic repeat request (HARQ) scheme with chase combining (CC) has very low complexity and is easy to combine with other techniques such as the coded-modulation and space–time coding, etc. However, the CC-HARQ scheme usually suffers from error and throughput performance degradation. A multiple decoding CC-HARQ (MDCC-HARQ) scheme is proposed in this paper by providing extra decoding chances when the joint decoding fails. Specifically, new LLR-sequences are constructed from the received signals, which can be utilized for the extra decoding attempts. Simulation results show that the proposed MDCC-HARQ scheme can achieve better error-performance and higher throughput efficiency, while requires less retransmission when compared with the CC-HARQ scheme.

Adaptive Packet Coding for Reliable Underwater Acoustic Communications

This work investigates adaptive random linear packet coding (RLPC) for reliable underwater acoustic (UWA) communications. Our goal is to minimize the total transmission time of data blocks by adjusting the packet coding rate. We first consider the application of RLPC with the conventional automatic repeat request (ARQ) scheme. We dynamically adjust the coding rate to fit the time variations of UWA channels by choosing the optimal number of packets in each transmission. The optimal number of packets in each transmission is obtained based on a dynamic programming (DP) algorithm according to the feedback messages, which contain the number of successfully transmitted packets in the last transmission and the channel state information. Furthermore, considering the long propagation delay of UWA communications, we propose a modified juggling-like ARQ (J-ARQ) for the RLPC scheme, for which the duration of each transmission can be adjusted based on the characteristics of RLPC. A two-step DP algorithm is proposed to find out the optimal solutions for this case. Simulation results show that the proposed schemes can improve the throughput efficiency and reduce the outage probability.

Markov‐based analysis for cooperative HARQ‐aided NOMA transmission scheme in 5G and beyond

AbstractIn the fifth generation (5G) wireless communication system, the non‐orthogonal multiple access (NOMA) scheme has recently been proposed as a possible candidate for improving spectral efficiency. We look at power‐domain NOMA in this study, in which, multiple simultaneous transmissions are allowed at the same channel with different transmission powers. To achieve reliable transmissions in NOMA, the hybrid automatic repeat request (HARQ) scheme can be integrated into NOMA. The performance of a downlink NOMA system using the Type I HARQ method is investigated in this research. This type of HARQ does not entail expensive device which is considered one of the requirements for a massive 5G‐based Internet of Things network. Unfortunately, in the literature, it has been shown that deriving closed‐form expressions for the outage probabilities of HARQ‐aided NOMA systems is intractable due to the incorporation of multiple fractional random variables. Consequently, in this article, we follow a simple yet efficient methodology to study our considered HARQ‐aided NOMA system. The HARQ‐assisted NOMA system on the downlink is modeled as an absorbing discrete‐time Markov chain (DTMC). Thereafter, under perfect and imperfect channel estimation, we use this model to examine system performance in terms of outage probability and estimated number of retransmissions. Interestingly, we demonstrate that our DTMC‐based analysis is straightforward, repeatable, and accurate. Moreover, in this article, we propose a cooperative HARQ (CHARQ) scheme for the downlink NOMA system. According to CHARQ, the users cooperate with the base station in the retransmission process that will result in improving the performance of NOMA. Monte Carlo simulations have been conducted to not only verify the accuracy of our DTMC‐based analysis, but also manifest the superiority of CHARQ over HARQ.

Adaptive Bit Rate Control in Semantic Communication With Incremental Knowledge-Based HARQ

Semantic communication has witnessed a great progress with the development of natural language processing (NLP) and deep learning (DL). Although existing semantic communication technologies can effectively reduce errors in semantic interpretation, most of these solutions adopt a fixed bit length structure, along with a rigid transmission scheme, which is inefficient and lacks scalability when faced with different meanings and signal-to-noise ratio (SNR) conditions. In this paper, we explore the impact of adaptive bit lengths on semantic coding (SC) under various channel conditions. First, we propose progressive semantic hybrid automatic repeat request (HARQ) schemes that utilize incremental knowledge (IK) to simultaneously reduce the communication cost and semantic error. On top of this, we design a novel semantic encoding solution with multi-bit length selection. In this fashion, the transmitter employs a policy network to decide the appropriate coding rate, so as to secure the correct information delivery at the cost of minimal bits. Moreover, a specific denoiser is further introduced to reduce the semantic errors encountered in the transmission process according to the semantic characteristics of context. Extensive simulation results have been conducted to verify the effectiveness of the proposed solution.

Multi-Device Low-Latency IoT Networks With Blind Retransmissions in the Finite Blocklength Regime

In future wireless communications, the Internet of Things (IoT) is a promising paradigm which is expected to connect massive number of devices while satisfying ultra-reliable and low latency communications (URLLC). In this article, we consider a multi-device IoT network supporting URLLC, where the data transmission process from the devices perform blind Automatic Repeat-reQuest (ARQ) or Hybrid ARQ (HARQ) via shared radio resources. We leverage recent advances in the characterization of coding rates and error probability in the finite blocklength regime to investigate the reliability and goodput performances of such network with both ARQ and HARQ schemes. Furthermore, both reliability-oriented and goodput-oriented designs are proposed for ARQ and HARQ schemes, respectively. In particular, we provide the optimal solutions for the error probability minimization problem, while efficient sub-optimal solutions for the goodput maximization problem are introduced, which show a tight performance in comparison to exhaustive search. Via simulation, the analytical results are validated and the system performance for both schemes are evaluated under variant setups with respect to total resources, packet sizes and SNR.

Analytical Model and Feedback Predictor Optimization for Combined Early-HARQ and HARQ

In order to fulfill the stringent Ultra-Reliable Low Latency Communication (URLLC) requirements towards Fifth Generation (5G) mobile networks, early-Hybrid Automatic Repeat reQuest (e-HARQ) schemes have been introduced, aimed at providing faster feedback and thus earlier retransmission. The performance of e-HARQ prediction strongly depends on the classification mechanism, data length, threshold value. In this paper, we propose an analytical model that incorporates e-HARQ and Hybrid Automatic Repeat reQuest (HARQ) functionalities in terms of two phases in discrete time. The model implies a fast and accurate way to get the main performance measures, and apply optimization analysis to find the optimal values used in predictor’s classification. We employ realistic data for transition probabilities obtained by means of 5G link-level simulations and conduct extensive experimental analysis. The results show that at false positive probability of 10−1, the e-HARQ prediction with the found optimal parameters can achieve around 20% of gain over HARQ at False Negative (FN) of 10−1 and around 7.5% at FN of 10−3 in terms of a mean spending time before successful delivery.

A novel adaptive code block group hybrid automatic repeat request scheme for low earth orbit satellite networks

SummaryLow earth orbit (LEO) satellite networks provide important support to expand 5G‐and‐beyond networks to realize global coverage. Hybrid automatic repeat requests (HARQs) can greatly improve the reliability of transmission through dynamic satellite channels. Due to the large propagation delay in LEO satellite channels, the biggest challenges of HARQ in satellite networks are the delayed channel state information (CSI) and overflow of receiver memory. In this paper, we propose a novel adaptive code block group HARQ (ACBG‐HARQ) scheme that achieves lower retransmission rates with reliable data receiving. First, we build a new channel state model (CSM) to describe the relationship between the packet error rate (PER) and global channel degradation. Three states of receiver memory allocation for HARQ are designed with respect to the channel state and memory occupation: idle state, non‐full state, and full state. Then, we propose an optimal HARQ scheme for LEO satellite networks with the Markov decision process (MDP) based on the fuzzy Q‐learning (FQL) algorithm to improve the accuracy of ACBG‐HARQ state transfer, which contributes to adaptive selection of the HARQ code block group size. Simulation results show that the ACBG‐HARQ scheme can achieve a maximum spectrum efficiency gain of 10% and that the probability of receiver memory overflow is reduced by 1%∼6%.

Age-Energy Tradeoff for Two-Hop Status Update Systems With Heterogeneous Truncated ARQ

Age of information (AoI) and energy cost (EC) are two key metrics in real-time remote monitoring systems. In this letter, we investigate the age-energy tradeoff for a short packet-based two-hop status update system, where the packet transmission may fail because of channel errors. In this case, the source can either retransmit the failed update to save EC for sensing, or generate a new one to maintain the AoI. Accordingly, we consider the truncated automatic repeat request (ARQ) scheme in both the first and second hops with different retransmission thresholds. Closed-form average AoI and average EC are given as a function of the failure probability and the thresholds of two hops. Moreover, a weighted sum of AoI and EC is minimized to tradeoff the age and energy. Numerical results demonstrate that increasing the difference between the thresholds of two hops can reduce the average AoI but increase the average EC, and an optimal packet length can always be identified to achieve age-energy tradeoff.

On the Secure Spectral Efficiency of URLLC With Randomly Located Colluding Eavesdroppers

In this article, we investigate the secure spectral efficiency of an ultrareliable low-latency communication system, where communications occur with short packets due to delay constraints, so that a finite blocklength formulation is considered. In addition, we assume that no feedback channel is available to implement automatic repeat request schemes, so that packet replication (PR) and interface diversity (ID) strategies are used to improve performance, which are then compared in terms of physical-layer security while considering a Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$m$ </tex-math></inline-formula> fading channel. Furthermore, we assume no knowledge of the instantaneous channel state information at Alice, neither with respect to Bob nor Eves, while the position of multiple colluding eavesdroppers are specified according to a Poisson point process. Numerical results show that the joint optimization of the blocklength, the transmit power, and the amount of information bits per codeword are crucial to maximize the secure spectral efficiency. In addition, we also show that ID outperforms the PR strategy in most scenarios when the number of replications/interfaces increases.

On the Self-Decoding of Polar-Coded HARQ

In this letter, we concern the self-decoding capability of polar-coded hybrid automatic repeat request (Polar-HARQ) schemes. The proposed self-decoding method enables the incremental redundancy (IR) based Polar-HARQ to recover all source bits solely using the retransmission codewords. It provides an extra decoding chance when the joint decoding attempt fails. With this, the final decoding success probability increases such that the number of retransmissions can be reduced and the system latency goes down. We derive one necessary condition for the successful self-decoding, which can also guide the optimization of Polar-HARQ. Three mainstream Polar-HARQ schemes are compared from the perspective of self-decoding. Simulation results validate the analysis.

A Novel LT Scheme without Feedback Messages for IoT of Smart City Scenarios

For IoTs of smart city scenarios always with the low cost, low power consumption, and high transmission delay properties, the traditional protocols based on feedback messages, e.g., the Automatic Repeat reQuest (ARQ) schemes, would dramatically affect the transmission efficiency. Therefore, the LT codes with only one feedback message in each entire coding process can be used to substitute the traditional protocols. As in many IoTs of smart city scenarios, the data must have both high transmission efficiency and timeliness requirements; thus, the negative effect of only the feedback message in each entire coding process cannot be neglected in such transmission environments. To enhance the transmission efficiency of such ensembles, a novel LT scheme without feedback messages is proposed in this paper. By presenting the definitions of optimal decoding overhead and recovery ratio per symbol, the optimal decoding overhead of LT codes can be found directly, then the encoding overhead of the encoder can be predesigned also. For this reason, the feedback messages in LT schemes can be removed. By using the proposed LT scheme, the transmission efficiency of IoT of smart city scenarios can be enhanced.

A Novel Efficient Secure and Error-Robust Scheme for Internet of Things Using Compressive Sensing

In most of existing Internet of Things (IoT) applications, data compression, data encryption and error/erasure correction are implemented separately. To achieve reliable communication, in particular, in harsh wireless environment with strong interference, error/erasure correction codes with higher correction capability or Automatic repeat request (ARQ) scheme are desirable but at the cost of increasing complexity and energy consumption. Due to resource-constrained IoT device, it is often challenging to implement all of them. In this paper, we propose a novel lightweight efficient secure error-robust scheme, ENCRUST, which is able to achieve these three functions using simple matrix multiplication. ENCRUST is built on the new theoretical foundation of projection-based encoding presented in this paper, by leveraging the sparsity inherent in the signal. We perform theoretical analysis and experimental study of the proposed scheme in comparison with the conventional schemes. It shows that the proposed scheme can work in low SINR range and the reconstructed signal quality shows graceful degradation. Furthermore, we apply the proposed scheme on real-life electrocardiogram (ECG) dataset and images. The results demonstrate that ENCRUST achieves decent compression, information secrecy as well as strong error recovery in one go.