Hybrid ARQ Scheme Research Articles

Tradeoff‐HARQ Scheme for Full‐Duplex SWIPT DF Relay

The SWIPT (simultaneous wireless information and power transfer) DF (decoding and forwarding) relay system could achieve the purpose of both increasing revenue and reducing expenditure. By analysing the system model and transmission characteristics of full‐duplex relay, this paper optimizes the retransmission slot structure to enhance the system performance. Firstly, the state transition model is established based on the analysis of the retransmission slot structure. Secondly, the state probability of each state and the transition probability between states are calculated to obtain the total data passing rate, energy transmission efficiency, and total transmission time. Thirdly, in order to compare the performance of various HARQ (hybrid automatic repeat request) schemes more effectively, JNTP (joint normalized throughput of information transmission and energy transmission) is constructed. Monte Carlo simulations finally confirm that the proposed tradeoff‐HARQ scheme outperforms the regular‐HARQ scheme in terms of JNTP: the performance of the tradeoff‐HARQ scheme is 0.03883 higher than that of the regular‐HARQ scheme when the total power limit is 20 dB and 0.00651 higher than that of the regular‐HARQ scheme when the total power limit is 30 dB.

Hybrid Automatic Repeat Request (HARQ) in Wireless Communications Systems and Standards: A Contemporary Survey

Automatic repeat request (ARQ) schemes, and in particular hybrid-ARQ (HARQ) schemes, which jointly adopt forward error correction (FEC) and ARQ, are essential to provide reliable data transmission in wireless communications systems. However, the feedback from the receiver to the transmitter and the retransmission process used in ARQ incurs significant cost in terms of power efficiency, throughput, computational power and delay. Unfortunately, such drawbacks can limit their applications to several current and emerging technologies. More specifically, the increasing number of wireless users has create spectrum scarcity, relying on small-size batteries create power constraints, deployment of real-time applications boost the demand for ultra-low delay networks, and the ultra-small low-cost Internet of Things (IoT) devices has limited signal processing and computation capabilities. Consequently, extensive research efforts have been dedicated to overcome the limitations inherent in HARQ. This survey paper provides an extensive literature review of the state-of-the-art HARQ techniques and discusses their integration in various wireless technologies. Moreover, it provides insights on advantages and disadvantages of particular ARQ types and discusses open problems and future directions.

Age-Optimal Transmission Policy With HARQ for Freshness-Critical Vehicular Status Updates in Space–Air–Ground-Integrated Networks

In this article, we investigate the freshness of the vehicular status updates in space–air–ground-integrated networks (SAGINs), where the status updates are generated by sampling a fixed-rate dynamic Markov process and delivered to the monitor over an unreliable channel instantaneously. The Age of Information (AoI) is adopted to capture the timeliness of the status updates. Two hybrid automatic repeat request (HARQ) schemes, namely, classical HARQ scheme and incremental redundancy HARQ (IR-HARQ) scheme, are taken into consideration to combat the errors occurred in the transmission. In this setting, once an update is not decoded successfully, one should carefully decide how to schedule the updates for optimizing the AoI. Especially, differential encoding scheme is introduced in the considered system to exploit the temporal correlations of the source. By differential encoding, each update can be actual or differential, based on the differential encoding level. To minimize the long-term average age, we formulate a Markov decision process (MDP), and prove that the optimal transmission policies for classical HARQ scheme and IR-HARQ scheme behave differently in threshold structures. Furthermore, we jointly optimize the codeword length, differential encoding level, and retransmission times to minimize the AoI. The performance comparison shows the advantages of the IR-HARQ scheme over the classical HARQ scheme from the age perspective.

On HARQ Schemes in Satellite-Terrestrial Transmissions

As an efficient supplement for terrestrial communications, e.g., fifth-generation communication networks, satellite communication has been proved as a promising choice to realize seamless coverage, due to its inherent superiority over common wireless communication systems, like large-scale coverage area and flexibility of deployment. In this article, a satellite-terrestrial transmission (STT) system including a satellite transmitter (S) and a group of terrestrial receivers (D) is focused on. Considering the randomness of D and employing stochastic geometry, the outage performance and diversity gain of three hybrid automatic repeat request (HARQ) schemes, generalized slotted ALOHA (GSA), repetition time diversity (RTD) and general incremental redundancy (IR), are respectively studied. In detail, the exact closed-form analytical expression for the outage probability (OP) is derived for the GSA scheme, while the approximated expression for the OP of RTD scheme is presented and a useful expression for the OP of IR scheme is derived. Furthermore, the diversity gains of the three considered HARQ schemes are respectively investigated in STT scenarios. Finally, some numerical results are provided to validate the proposed analysis models.

Energy Efficient Network Coding HARQ Transmission Scheme for S-IoT

Satellite-based Internet of Things (S-IoT) is suggested to meet the emergency applications and services of ubiquitous terrestrial IoT user equipments (UEs) in the future IoT. Since the limited power constraints of the satellite and the IoT UEs, it is a vital challenging to design an energy efficient transmission scheme, which can reduce the number of retransmission rounds while offer high throughput. In this article, we combine the network coding and hybrid automatic repeat request (HARQ) to propose a network coding HARQ (NC HARQ) transmission scheme for typical S-IoT scenarios, i.e., the multiple unicast downlink transmission and network coding bidirectional relaying scenarios. We derive the theoretical expressions for the metrics of system performance, including the average number of transmission rounds, the system throughput and the energy efficiency (EE). Specifically, our derivations are completed in two methods, i.e., the mutual information cumulation method and the matrix exponential (ME) distribution method. Based on the above analytical results, we formulate and solve the maximum EE optimization problem to obtain the optimal maximum transmission rounds in two typical communication scenarios. Simulations are provided to validate our analytical results, and confirm the improvement of our proposed NC HARQ scheme.

Real-Time Status Updates With Perfect Feedback Over Erasure Channels

Real-time decision making relies on the availability of accurate data and, therefore, delivering status updates in a timely fashion is of paramount importance. The topic of real-time status updates has received much attention in recent years. This article contributes new results to this research area by studying the interplay between average timeliness and design decisions made at the physical layer, for unreliable communication channels. Specifically, this study explores the tension between the fact that more reliable transmissions with lower probabilities of decoding failure tend to improve timely delivery, unless these improvements come at the expense of significantly longer codewords. The average timeliness is adopted as an evaluation criterion, and a framework to efficiently compute the performance of various transmission schemes for the binary erasure channel is developed. We show that the average timeliness decreases as we increase the feedback rate in a hybrid ARQ scheme for a range of codeword lengths. This article also provides design guidelines for the codeword length selection for an hybrid ARQ scheme to improve the average information timeliness. Numerical examples are included to further illustrate the applicability of our findings.

Physical layer rateless codes for the SATCOM on‐the‐move system with blockage

SummaryPhysical layer rateless codes are employed to mitigate the link‐blockage in satellite communication on‐the‐move (SOTM) systems. Both nonsystematic raptor (NR) codes and systematic raptor (SR) codes are investigated, where the blockage‐channel is modelled as an additive white Gaussian noise‐contaminated binary erasure channel (AWGN‐BEC). The asymptotic performance of NR codes is obtained by extrinsic information transfer (EXIT) method, and it is proved theoretically that NR codes have capacity‐approaching performance on this channel. A modified EXIT method is proposed to analyze the asymptotic performance of SR codes since the channel outputs not only continuous message but also discrete message. Due to the poor performance of existing SR codes on blockage‐channels, the degree distributions are optimized and the resulting codes show much better performance. Moreover, the raptor codes are compared with hybrid automatic repeat request (HARQ) schemes in satellite communication systems.

Analysis of Peak Age of Information in Blocking and Preemptive Queueing Policies in a HARQ-Based Wireless Link

In this letter, we focus on evaluating Peak Age-of-Information (PAoI) in a typical wireless link in which each packet transmission is successful with some probability. The receiver applies a hybrid ARQ (HARQ) scheme such as chase combining to decode each packet. Thus, several transmissions of the same packet lead to a sequence of strictly increasing successful packet reception probabilities. Moreover, the number of transmissions for each packet is limited. In this link, when the packets are generated randomly, we compare two queueing policies at the transmitter, i.e., blocking and preemptive. The former exploits the capability of HARQ to send the packet to the destination sooner, but the latter tries to send the fresher packets to the destination. We derive analytically the average PAoI at both policies and compare them in different situations.

Analyzing Grant-Free Access for URLLC Service

5G New Radio (NR) is expected to support new ultra-reliable low-latency communication (URLLC) service targeting at supporting the small packets transmissions with very stringent latency and reliability requirements. Current Long Term Evolution (LTE) system has been designed based on grant-based (GB) (i.e., dynamic grant) random access, which can hardly support the URLLC requirements. Grant-free (GF) (i.e., configured grant) access is proposed as a feasible and promising technology to meet such requirements, especially for uplink transmissions, which effectively saves the time of requesting/waiting for a grant. While some basic GF access features have been proposed and standardized in NR Release-15, there is still much space to improve. Being proposed as 3GPP study items, three GF access schemes with Hybrid Automatic Repeat reQuest (HARQ) retransmissions including Reactive, K-repetition, and Proactive, are analyzed in this article. Specifically, we present a spatio-temporal analytical framework for the contention-based GF access analysis. Based on this framework, we define the latent access failure probability to characterize URLLC reliability and latency performances. We propose a tractable approach to derive and analyze the latent access failure probability of the typical UE under three GF HARQ schemes. Our results show that under shorter latency constraints, the Proactive scheme provides the lowest latent access failure probability, whereas, under longer latency constraints, the K-repetition scheme achieves the lowest latent access failure probability, which depends on K. If K is overestimated, the Proactive scheme provides lower latent access failure probability than the K-repetition scheme.

Modeling and Analysis of Hybrid ARQ Scheme for Incremental Cooperative Communication in Underwater Acoustic Sensor Networks

Underwater acoustic sensor network (UASN) is a vast network, in which the neighborhood of a transmitting node consists of many operating sensor nodes. By considering this as an advantage, we propose a hybrid automatic repeat request scheme for incremental cooperative communication (HARQ-INCC) in UASNs. The proposed scheme utilizes neighborhood sensor nodes during the instance of packet retransmission. It combines HARQ scheme with incremental cooperative communication; to enhance reliability and to optimize the energy efficiency. In this article, we present an analytical model to calculate the energy efficiency in UASNs for deep and shallow water scenarios, by examining the influence of acoustic fading, ambient noises and underwater channel characteristics. The analytical results show that HARQ-INCC outperforms the existing techniques for considerable distances between the source and destination nodes. We further propose an optimization algorithm to maximize the energy efficiency, by adjusting the modulation level and packet size as a function of the distance between source and destination nodes. The proposed optimization algorithm significantly enhances the energy efficiency of HARQ-INCC scheme. Finally, we analyze the energy efficiency of UASNs with respect to the variation in environmental parameters like waves and shipping noises. We validate the analytical results using ns-3 simulations.

Throughput Analysis of Low-Latency IoT Systems With QoS Constraints and Finite Blocklength Codes

Internet of Things (IoT) is a promising paradigm to connect massive number of devices in future wireless communications while satisfying various quality of service (QoS) requirements. In this paper, we consider a QoS-constrained IoT system operating with finite blocklength (FBL) codes to support low latency communications. Two data arrival models are considered, namely, constant-rate arrival and ON-OFF discrete-time Markov arrival. The throughput performance is studied for both arrival models under statistical queuing constraints and deadline limits. For the scenario with instantaneous channel state information (CSI), we derive the QoS-constrained throughput expressions for both arrival models. Subsequently, an instantaneous-CSI-driven optimal power control algorithm is proposed to maximize the throughput, while guaranteeing a certain reliability target. In addition, we consider a scenario with only average CSI being available at the transmitter and propose to apply hybrid automatic repeat request (HARQ) schemes to improve the FBL performance. The decoding error probability and the outage probability are first characterized, following which the distribution of transmission period is derived. Furthermore, the throughput expressions are provided for both types of arrivals. Via numerical analysis, the impact of error probability, fixed transmission rate, coding blocklength, and QoS constraints on the throughput is studied.

Performance Evaluation of HARQ-Assisted Hybrid Satellite-Terrestrial Relay Networks

This letter investigates the delay-limited throughput of a satellite-terrestrial relay network with hybrid automatic repeat request (HARQ) protocol in which a satellite communicates with a user with the aid of an amplify-and-forward (AF) terrestrial relay. Particularly, the proposed analysis includes both the channel state information (CSI)-assisted and the fixed gain AF relaying protocols for two representative HARQ schemes, namely, chase combining (CC) and incremental redundancy (IR). Numerical results are provided to evaluate the performance of different HARQ schemes and relay protocols, and also indicate the impact of key parameters, such as the HARQ round number and target information rate, on the achievable performance.

Age-Optimal HARQ Design for Freshness-Critical Satellite-IoT Systems

In this article, we consider the satellite Internet of Things (IoT) system, in which the IoT device observes physical processes and transmits the status updates to the monitor node over an error-prone channel with nontrivial propagation delay. The freshness of status updates is characterized by Age of Information (AoI), a novel metric that is defined as the time that elapsed since the freshest received status update was generated. Channel coding is used to combat the burst channel errors and feedback is available through hybrid automatic repeat request (HARQ) protocols. By adopting both the simple-HARQ and incremental redundancy HARQ (IR-HARQ) transmission schemes, we study the age-optimal redundancy allocation problems under the constraint of reliability. As we put special interests on the satellite-IoT scenarios in which the propagation delays are nonnegligible, there exists a threshold of the propagation delay only below which using retransmissions is beneficial to AoI. However, the characterization of such a threshold has received little attention in the literature. By formulating and solving the age-optimal redundancy allocation problems for the adopted HARQ schemes, explicit expressions of the optimal codeword length for each transmission round are derived, and then the threshold of the propagation delay for beneficial retransmissions is obtained. Extensive numerical analysis is conducted to show the effects of propagation delay and channel state on the redundancy allocation results and the optimal AoI. The threshold is also demonstrated by numerical analysis. The results shed important light on the age-optimal HARQ design for freshness-critical satellite-IoT systems in the presence of nontrivial propagation delay.

A secured and reliable communication scheme in cognitive hybrid ARQ-aided smart city

Due to advancements in communication technologies, specifically, the Internet of Things (IoT)-based smart cities, the allocation of spectral bands is a major challenge. To overcome this challenge, the cognitive radio network (CRN) has widely been accepted for efficient utilization of the available spectrum. Hence, efficient spectrum utilization and secured communication have attracted significant attention in recent years. However, due to the involvement of smart wireless devices in CRN, the cognitive radio (CR) systems are vulnerable to security threats that mainly target the weaknesses of CR communication and networking. Considering the efficient utilization of spectrum and secured smart city applications, this paper proposes a Secured and Reliable Cognitive Hybrid Automatic Repeat reQuest (SRC-HARQ) scheme. The SRC-HARQ models the primary user (PU) channel by Hidden Markov Model (HMM) to identify the unoccupied spaces. Based on the HMM results, the cluster head (CH) in a smart city determines the activity pattern of PUs and detects idle channels. After the detection of an idle channel, the CH broadcasts a beacon. Upon the reception of a beacon, each member node responds with a ready-to-send (RTS) message along with an encrypted message. The CH replies with a clear-to-send (CTS) signal after the successful decryption of the received message. Furthermore, a 4-state Markov Chain is used for reliability in terms of false alarm and misdetection. The closed-form expressions for mean packet delay, end-to-end delay, and throughput are derived and validated using Monte Carlo simulations.

Cache-Aided Cooperative Device-to-Device (D2D) Networks: A Stochastic Geometry View

Caching is a promising technique for 5G networks to reduce the backhual traffic and increase the overall network efficiency. In this paper, we study the caching placement policy with consideration of cooperative transmission for a two-hop relay-enabled device-to-device (D2D) network. In the caching placement phase, the probabilistic caching placement policy is considered, and in the content transmission phase, the hybrid automatic repeat request (HARQ) scheme with soft information combining [i.e., energy accumulation (EA) and mutual-information accumulation (MIA)] is utilized to improve the content retrieval experience. Cache-aided successful transmission probability (CSTP) is adopted as the main performance metric in this paper. By using tools from stochastic geometry, analytical expressions for the CSTP under different transmission schemes are derived. In moderate or high SIR regime, the optimal caching placement policy is identified based on the analytical expression and the CSTP performance is maximized accordingly. Evaluation results suggest that the MIA-based caching strategy performs better as opposed to existing strategies in most cases, but this outperformance vanishes when the transmission environment becomes severe or when users’ requests become concentrated.

Design and performance evaluation of bitwise retransmission schemes in wireless sensor networks

The previously proposed bitwise retransmission schemes which retransmit only selected bits to accumulate their reliability are designed and evaluated. Unlike conventional automatic repeat request (ARQ) schemes, the bitwise retransmission schemes do not require a checksum for error detection. The bitwise retransmission decisions and combining can be performed either after demodulation of the received symbols or after channel decoding. The design and analysis assume error-free feedback, however, the impact of feedback errors is also considered. The bit-error rate (BER) expressions are derived and verified by computer simulations in order to optimize the parameters of the retransmission schemes. The BER performance of coded and uncoded bitwise retransmissions is compared with a hybrid ARQ (HARQ) scheme over additive white Gaussian noise (AWGN), slow fading, and fast fading channels. It is shown that bitwise retransmissions outperform block repetition coding (BRC) over AWGN channels. In addition, the selection diversity created by the bitwise retransmissions can outperform the HARQ at large signal-to-noise ratio (SNR) over fast fading channels. Finally, the practical design of a bitwise retransmission protocol for data fusion in wireless sensor networks is presented assuming Zigbee, WiFi and Bluetooth system parameters.

Soft Iterative Decoding Algorithms for Rateless Codes in Satellite Systems

The satellite system is one of the most efficient means for broadcasting due to its wide service coverage as well as the fact that it can provide high data rate services by using high frequency bands. However, there are a number of problems in the satellite system, such as a long round trip delay (RTD) and heterogeneity of the channel conditions of the earth stations. Even though utilizing adaptive coding and modulation (ACM) is almost mandatory for the satellite systems using high frequency bands due to the serious rain fading, the long RTD makes it difficult to quickly respond to channel quality information, resulting in a decrease in the efficiency of ACM. A high heterogeneity of earth stations caused by a wide service coverage also makes it difficult to apply a uniform transmission mode, and thus satellite systems require receiver-dependent transmission modes. A rateless code can be an effective means to compensate for these disadvantages of satellite systems compared to terrestrial wireless systems. This paper presents soft iterative decoding algorithms for efficient application of rateless codes in satellite systems and demonstrates that rateless codes can be effectively used for hybrid automatic repeat request schemes.

Performance analysis of LT code-based HARQ error control in underwater acoustic sensor networks

Underwater acoustic sensor network (UASN) is an emerging technology meant for underwater explorations. In underwater communication, the acoustic signal travels a longer distance with smaller bandwidth. Characteristics of the acoustic channel and the distance between underwater sensor nodes vary with time due to the variations in the water current. This affects the channel quality as well as the topology of the network. Connectivity issues in UASN cause transmission reliability challenges, in transferring the data sensed by various sensor nodes to the other end. Thus, data reliability and energy efficiency are the two critical issues in the case of UASN. The robust signal attenuation leads to the reception of erroneous data or data loss. In this paper, Recursive Luby transform (RLT) code-based Hybrid Automatic Repeat reQuest is proposed to overcome the data reliability issues and to obtain transmission efficiency. RLT is a form of Luby transform code with small degree of distribution. The proposed rateless code-based Hybrid ARQ scheme combines the RLT code and selective retransmission ARQ (RLTCH). The RLT code is adopted for its minimal complexity in encoding and decoding processes. The performance of RLTCH is evaluated by considering the underwater-specific channel characteristics. Simulation results of RLTCH for multi-hop UASN reveal that the proposed technique increase the network throughput with reduced energy consumption and end-to-end delay. Comparative performance studies were conducted to confirm the superiority of RLTCH with other schemes based on parameters such as throughput, packet arrival ratio, delay and energy consumption.

On the Impact of Time-Correlated Fading for Downlink NOMA

This paper investigates the performance of non-orthogonal multiple access (NOMA) systems over time-correlated Rayleigh fading channels, where the users have heterogeneous quality of service requirements, e.g., a latency-critical user with a low target rate and a delay-tolerant user with a large target rate. In order to meet the different requirements of the users, two partial hybrid automatic repeat request (HARQ) schemes, including partial HARQ with chase combining (HARQ-CC) and HARQ with incremental redundancy (HARQ-IR), are proposed. The closed-form expressions of outage probabilities for NOMA with and without re-transmission are derived. With the developed outage probabilities, a condition on the superiority of NOMA to orthogonal multiple access (OMA) is obtained. In particular, the condition is characterized by the transmit powers for NOMA without re-transmission and is obtained by using the bisection method in the case with re-transmission. To further improve the performance of the HARQ enabled NOMA schemes, we consider an average transmit power minimization problem by optimizing the transmit power among different transmission rounds with outage constraints. However, due to the complexity of the developed outage probabilities, the formulated problem is non-convex and challenging to solve. Then we approximate the original problem by deriving the upper-bound approximations of the outage probabilities and solve it by using the geometric programming method. Simulation results demonstrate the accuracy of the developed analytical results. It is shown that the performance of NOMA is superior to OMA, only when the obtained condition is satisfied. HARQ-CC and HARQ-IR can enhance the outage performance of NOMA over time-correlated fading channels and the HARQ-IR has excellent performance in terms of energy efficiency.

HARQ-Chaotic: Analog Chaotic Code Applied in HARQ Scheme of Wireless Communication System

This paper proposes a novel symbol-level combining hybrid automatic repeat request (HARQ) scheme based on analog chaotic code and named HARQ-Chaotic. The transmitter of HARQ-Chaotic adopts analog chaotic code to encode Quadrature Amplitude Modulation (QAM) symbols of retransmission packets to combat fading and noise. As the analog chaotic code can only handle sources with amplitudes in the range of [-0.5, 0.5], QAM symbols must be scaled into this range. We derived the optimal scaling factor through theoretical analysis. A joint algorithm combining with novel soft chaotic decoder and novel soft QAM demapper is proposed for the receiver to enhance the performance of the whole communication system. We implemented HARQ-Chaotic with LDPC codes and 16-QAM/64-QAM to carry out simulations in both AWGN channels and multipath fading channels. Massive simulation results demonstrate that the proposed HARQ-Chaotic has 1dB-4dB gain over traditional HARQ-Chase combining (HARQ-CC) scheme in block error rate (BLER) performance.