Repeat Request Mechanism Research Articles

On Coordinated Scheduling of Radio and Computing Resources in Cloud-RAN

Cloud Radio Access Network is a promising mobile network architecture based on centralizing the baseband processing of many cellular base stations in a BBU (BaseBand Unit) pool. Such architecture has many advantages. However, computing resources are shared among the base stations connected to the BBU pool. It is challenging to schedule the processing of users’ data, especially on overloaded BBU pools, while respecting the time constraints imposed by the Hybrid Automatic Repeat Request (HARQ) mechanism. Given that the processing time of users’ data and the computing requirement depends on the radio parameters such as the Modulation and Coding Scheme (MCS), we propose to enable the coordination between radio and computing resources schedulers; such coordination makes the selection of MCS dependent on the availability of radio and computing resources and on the ability to process data while respecting the HARQ-deadline. In this context, we propose and evaluate three Integer Linear Programming (ILP)-based schemes and three low-complexity heuristics, demonstrating their ability to reduce the wasted transmission power. Moreover, we evaluate the performance of the coordination under a multi-services scenario consisting of two services having heterogeneous requirements, enhanced Mobile Broadband (eMBB) and Ultra-Reliable Low-Latency Communication (URLLC).

Performance Modeling and Analysis of BASUR-CARQ Protocol Based on Interrelay Interference Cancellation

To recover the performance loss of nodes in half-duplex mode, this paper proposes a buffer-aided successive relay protocol based on cooperative automatic repeat request mechanism (BASUR-CARQ). Based on the fact that interrelay interference (IRI) will occur when relay nodes transmit or receive simultaneously, an interference cancellation operator is proposed to determine whether the interference is eliminated to reduce the outage probability. Moreover, a delay model for data frame transmission is proposed based on CARQ mechanism, and a closed-form expression for the average delay is derived. A 6-state discrete-time Markov chain (DTMC) model is developed to obtain the system throughput, and a closed-form expression for the system energy efficiency under M-ary modulation is derived. Finally, the simulation results show that with the setting of parameters that can balance the main performance, the delay performance of BASUR-CARQ protocol is significantly enhanced compared to the traditional protocols, and the throughput of BASUR-CARQ protocol is also optimized at high signal-to-noise ratio (SNR). Meanwhile, the energy efficiency of BASUR-CARQ protocol is significantly improved for the successive relay communication system without interference cancellation technique.

Swift HARQ Based on Machine Learning for Latency Minimization in URLLC

Ultra-reliable low-latency communication (URLLC) has been introduced in the 5th Generation (5G) radios for mission-critical applications that demand strict reliability and latency traffic to guarantee the rapid delivery of short packets (up to 1 ms) with a success probability rate of 99.999%. The challenging reliability and latency requirements of URLLC have significant impact on the air-interface design, especially on the Hybrid Automatic Repeat reQuest (HARQ) mechanism. This study focuses on satisfying link latency requirements by reducing the delay that arises in the presence of the HARQ operation. To this end, we propose a Swift HARQ protocol empowered by machine learning techniques to estimate the decodability of a packet early enough within its maximum number of allowable retransmission attempts. This can allow the transmitter to react faster by dropping the non-decodable packets, or activating the repetition mode where parts of the HARQ feedback can be omitted. As shown through system-level simulations, the proposed model achieves a delay reduction of more than 50% compared to the traditional HARQ, and increases the system throughput by up to 40% when multiple HARQ retransmissions are required.

Multi-sector discrete-time channel model for data link layer evaluation of CubeSat communications

Innovation in the space sector is going through a fruitful period. Among other factors, this has been a consequence of the CubeSat paradigm and its acceptance in the educational, scientific, and commercial sectors, as well as its relevant role in the integration of terrestrial and satellite communication systems. Nevertheless, there is no standardized communication protocol for CubeSat technology. One of the reasons for this lack of standardization is the nonexistence of a widely accepted communication channel model for fast development and simulation of CubeSat technology at the data link layer level. Aiming at filling this gap, we propose a communication channel model that captures both the dynamics of the CubeSat in the low earth orbit and the propagation environment where the terrestrial devices are located, taking into account the elevation angle. For this purpose, finite state Markov chains are used to model the time evolution of the channel fading through the satellite trajectory when it passes by the ground point target. Then, CCSDS recommendations are used as a study case for the data link layer of a CubeSat, while an adaptive automatic repeat request mechanism, according to the elevation angle, is simulated and optimized, showing the usefulness of the proposed channel model.

Physical layer forwarding for 5G multi-hop Backhaul networks

In 5G networks, an integrated access and backhaul network is formed to connect IAB-nodes to the core network via an IAB-donor. To support multi-hop communications in this network, an adaptation-layer forwarding mechanism has been specified in the standard. However, the end-to-end delay achieved by such a mechanism cannot satisfy the requirement of delay-sensitive traffic. To this end, a PHY-layer forwarding mechanism is designed to complement the adaptation-layer forwarding mechanism. In the PHY-layer forwarding mechanism, when a transport block (TB) is received, it is first determined whether or not the TB is forwarded at the PHY layer, based on an ingress indicator that is sent prior to the transmission of the TB. If the ingress indicator shows that the TB is to be forwarded at the PHY layer, the indicator is mapped to an egress indicator that will be sent as an ingress indicator for a certain next-hop node. The process of ingress–egress indicator mapping can be conducted in parallel with TB decoding, so it does not cause additional forwarding delay. To improve the reliability of PHY-layer forwarding, the TB is buffered until it is successfully received, which is achieved by exploiting the hybrid automatic repeat request (HARQ) mechanism of 5G new radio (NR). The end-to-end delay of the PHY-layer forwarding mechanism and the adaptation-layer forwarding mechanism are analyzed and also evaluated via simulations. Performance results show that the PHY-layer forwarding mechanism reduces the end-to-end delay by more than 40% compared with the adaptation-layer forwarding mechanism under various system parameters.

HARQ in Full-Duplex Relay-Assisted Transmissions for URLLC

The Release 16 completion unlocks the road to an exciting phase pertain to the sixth generation (6G) era. Meanwhile, to sustain far-reaching applications with unprecedented challenges in terms of latency and reliability, much interest is already getting intensified toward physical layer specifications of 6G. In support of this vision, this work exhibits the forward-looking perception of full-duplex (FD) cooperative relaying in support of upcoming generations and adopts as a mean concern the critical contribution of hybrid automatic repeat request (HARQ) mechanism to ultra-reliable and low-latency communication (URLLC). Indeed, the HARQ roundtrip time (RTT) is known to include basic physical delays that may cause the HARQ abandonment for the 1 ms latency use case of URLLC. Taking up these challenges, this article proposes a hybrid FD amplify-and-forward (AF)-selective decode-and-forward (SDF) relay-based system for URLLC. Over this build system, two HARQ procedures within which the HARQ RTT is shortened, are suggested to face latency and reliability issues, namely, the proposed and the enhanced HARQ procedures. We develop then an analytical framework of this relay based HARQ system within its different procedures. Finally, using Monte-Carlo simulations, we confirm the theoretical results and compare the proposed relay-assisted HARQ procedures to the source-to-destination (S2D) HARQ-based system where no relay assists the communication between the source and the destination.

Reliable Video Multicasting over WLANs

As is known reliable multicast transmission is not addressed in WLANs. Multicast packets are sent over wireless channels without using medium access control (MAC) layer automatic repeat request (ARQ) mechanism. Therefore, packet error rates will be very high. This paper investigates reliable video multicasting, which became a very popular application, over WLANs. To this end, application layer forward error correction (AL-FEC) codes based on Raptor Q can be used as a means to provide reliable delivery of the multicast video encoded with the H.264/Advanced video coding (AVC) codec. Since video streaming applications have very stringent Quality of Service requirements (low delay and error free transmission of packets), the Raptor Q and the H.264/AVC parameters have to be determined depending on the QoS of the video. Therefore, in this work an advanced cross-layer simulator was developed to analyse the performance of the end-to-end system. Simulation results show that using AL-FEC significantly improve the received video quality, i.e., the mean peak signal to noise ratio (PSNR) is improved over 34 dB. Further that it is shown that frequently inserting intra-frame results in poor video quality. Therefore, it is suggested to send intra frame at longer intervals.

Communication Network Topology Inference via Transfer Entropy

In this work, we consider the problem of inferring links in a communication network, using limited, passive observations of network traffic. Our approach leverages transfer entropy (TE) as a metric for quantifying the strength of the automatic repeat request (ARQ) mechanisms present in next-hop routing links. In contrast with existing approaches, TE provides an information-theoretic, model-free approach that operates on externally available packet arrival times. We show, using discrete event simulation of a wireless sensor network, that the TE based topology inference approach described here is robust to varying degrees of connection quality in the underlying network. Compared to an existing approach which uses the linear regression based formulation of Granger Causality for network topology inference, our approach has better asymptotic time complexity, and shows significant improvement in network topology reconstruction performance. Our approach, though sub-optimal, also has better time complexity, while still retaining reasonable performance, compared to a causation entropy based optimal algorithm proposed in the literature.

Prioritized Retransmission: A TCP Flow Control Mechanism

Now-a-days, efforts have been made in the research of transmission control protocols to improve the performance of the flow control mechanism. Internet communication and services daily increase the variety and quantity of their capacity and needs. Therefore the flow control mechanism will have to consider valuable for traffic control, especially on high-speed networks. Initially there are some challenges, for instance, loss of packet, processing capacity, performance, buffer overflows and deadlocks with which daily traffic is confronted. This paper analyzes and reviewed the strengths and weaknesses of the different flow control mechanisms used in TCP. To overcome the weaknesses of these flow controls, we suggest a priority retransmission mechanism. Here we have priority on the Negative Acknowledgment (NACK), we resend the package on the basis of the minimum sequence number of the NACK. In buffer of priority retransmission Automatic Repeat request (ARQ) mechanism, the packet is released to the communication link in a First in First out (FIFO) manner. That is why the priority retransmission ARQ gives the optimum performance.

Enhanced Mathematical Modeling of Aggregation-Enabled WLANs with Compressed BlockACK

Aggregation-enabled wireless local area networks (WLANs) have an automatic repeat-request (ARQ) mechanism called a block acknowledgement window (BAW), which has a significant impact on frame aggregation size, throughput, and delay under noisy channel conditions. While accurate estimations of network performance are essential for traffic engineering and guaranteed quality of service, the existing mathematical modeling approaches do not include BAW operations, and thus, are not applicable to aggregation-enabled WLANs with BAW mechanism. In this paper, we propose a new and accurate Markov chain model to estimate the average aggregation size resulting from BAW operations under noisy channel conditions. The obtained average aggregation size is used in the proposed enhanced performance model of aggregation-enabled WLANs. Our numerical and simulation analysis shows that, for 50 nodes transmitting saturated uplink traffic on a channel with a packet error rate (PER) of 0.25, ignoring the BAW operations when modeling the current protocol results in throughput and access delay errors as high as 55 and 77 percent, respectively; but the proposed enhanced model, which captures the BAW's impact, produces less than 2.5 percent errors in throughput and access delay estimations.

Average Throughput Analysis and Optimization in Cooperative IoT Networks With Short Packet Communication

Internet of Things (IoT) is a promising paradigm to provide massive wireless connections in the future communications. One main feature of IoT is short packet communication (SPC), which adopts finite block-length codewords for data transmissions. Different from the long packet transmission (i.e., infinite block-length codewords) in conventional wireless networks, SPC suffers from a significant packet error rate even when the transmission rate is smaller than the Shannon capacity. To enhance the transmission efficiency as well as the reception reliability, we introduce cooperative relaying to the IoT network and propose a cooperative IoT protocol. Then, we analyze the average throughput of the cooperative IoT protocol with an approximated closed-form expression. Based on the closed-form expression, we design both optimal and suboptimal transmission rates to maximize the average throughput. Numerical and simulation results have validated the correctness of the theoretical analysis, and show that the maximum average throughput with the optimal/suboptimal design almost overlaps with the simulation results. Besides, we compare the proposed protocol with the automatic repeat request (ARQ) mechanism in terms of both the optimal transmission rate and the maximum average throughput, and observe that the proposed protocol outperforms the ARQ mechanism, especially for a medium/large number of cooperative users.

Analysis of channel uncertainty in ARQ relay networks.

Several power allocation algorithms for cooperative relay networks are presented in the literature. These contributions assume perfect channel knowledge and capacity achieving codes. However in practice, obtaining the channel state information at a relay or at the destination is an estimation problem and can generally not be error free. The investigation of the power allocation mechanism in a wireless network due to channel imperfections is important because it can severely degrade its performance regarding throughput and bit error rate. In this paper, the impact of imperfect channel state information on the power allocation of an adaptive relay network is investigated. Moreover, a framework including Automatic Repeat reQuest (ARQ) mechanism is provided to make the power allocation mechanism robust against these channel imperfections. For this framework, the end-to-end SNR is calculated considering imperfect channel knowledge using ARQ analytically. The goal is to emphasize the impact of imperfect channel knowledge on the power allocation mechanism. In this paper, the simulation results illustrate the impact of channel uncertainties on the average outage probability, throughput, and consumed sum power for different qualities of channel estimation. It is shown that the presented framework with ARQ is extremely robust against the channel imperfections.

A Novel Error Correction Mechanism for Energy-Efficient Cyber-Physical Systems in Smart Building

Smart building is an effective solution to address the issue of energy consumption in today’s cyber-physical systems (CPSs) connected world. As an important tool to collect information from a fleet of electric appliance that installed in the building scope, a wireless sensor network is widely employed for this purpose. In this paper, we propose to incorporate forward error correction into the media access control layer of IEEE 802.15.4 standard for packets transmission, as the originally used automatic repeat request mechanism is a timing and energy consumed process that should be avoided in a noisy wireless channel of a smart building environment. Based on the developed CPS simulation platform, the bits error rate and packets error rate of convolutional codes (CCs), Reed-Solomon (RS) codes, and their concatenated codes are intensively investigated, on condition of been applied to different packet length and code rates. We show that the CCs are superior to other codes in most cases. However, the RS and CCs concatenated codes are good candidates, and the RS codes with larger symbol length are preferred for a longer packet. In this regard, future research will concentrated on non-line-of-sight wireless channel, and take the pulse interference from other devices into account.

ASRQ: Automatic Segment Repeat Request for IEEE 802.15.4-Based WBAN

In a wireless body area network (WBAN), high data reliability and long operating time are important requirements. The retransmission process of the default Automatic Repeat reQuest (ARQ) mechanism in IEEE 802.15.4 is a suitable method to ensure the data reliability of WBAN communications, where frame loss can occur frequently. However, retransmitting the entire DATA frame is energy inefficient due to the fact that the most of payload data within lost frames are only partially corrupted. Therefore, this paper proposes the automatic segment repeat request scheme for the IEEE 802.15.4-based WBANs. The proposed scheme partitions the data payload into segments when the channel condition is bad, and retransmits only the corrupted segment(s). This reduces the size of the retransmitted frames, which improves frame reception rate and decreases the amount of transmitted traffic, and thus energy consumption. Our experiments using a real IEEE 802.15.4-based WBAN test bed show that the proposed method provides higher transmission reliability and lower power consumption than the default IEEE 802.15.4 ARQ mechanism.

English

Video transmission over the wireless network faces many challenges. The most critical challenge is related to packet loss. To overcome the problem of packet loss, Forward Error Correction is used by adding extra packets known as redundant packet or parity packet. Currently, FEC mechanisms have been adopted together with Automatic Repeat request (ARQ) mechanism to overcome packet losses and avoid network congestion in various wireless network conditions. In the current Adaptive FEC mechanism, the FEC packets are decided by the average queue length and average packet retransmission times. The Adaptive FEC mechanisms have been proposed to suit the network condition by generating FEC packets adaptively in the wireless network. However, the current Adaptive FEC mechanism has some major drawbacks such as the reduction of recovery performance which injects too many excessive FEC packets into the network. This is not flexible enough to adapt with varying wireless network condition. Therefore, the enhancement of Adaptive FEC mechanism (AFEC) known as Enhanced Adaptive FEC (Enface) has been proposed. The aim is to improve recovery performance on the current Adaptive FEC mechanism by injecting FEC packets dynamically based on varying wireless network conditions. Based on the findings, the optimal amount of FEC generated by Enface mechanism can recover high packet loss and produce good video quality An Enhanced Random Early Detection Forward Error Correction (ERED-FEC) mechanism is implemented to improve the quality of video transmissions over Wireless Local Area Networks (WLANs).

QoS-aware Opportunistic Cooperative ARQ Mechanism of Sensors Based on Channel state Sensing for Internet of Things

It is well known that the performance of Internet of Things application services is easy to be affected by internal noise of sensor, external environment interference and constriction of system resource. In order to solve the above problems, we studied the characteristics of bit error rate, outage ratio, signal to noise, and scale of relay sensors with channel state to choose the optimal transmission control scheme between direct mode and cooperative mode, building upon which we proposed the opportunistic cooperative automatic repeat request (ARQ) mechanism based on the rules and features of throughput ratio, average delay, packet error rate and energy efficiency, in consideration of retransmission time and channel quality. More importantly, the proposed opportunistic cooperative ARQ mechanism could set up the max retransmission time and control the progress of cooperative transmission according to the real-time network and sensor state, as well as Quality of Services (QoS) guarantee requirements of Internet of Things applications. The mathematical analyses and experiment results show that the proposed scheme is superior to the QoS provisioning schemes based on cooperative ARQ alone and direct transmission with channel state alone in terms of reliability, real time performance and life cycle of system, as well as energy efficiency.

신뢰성 있는 멀티캐스트 서비스를 위한 스프레딩 코드 기반 피드백 기법

In order to support reliable medium access control (MAC) layer multicast services in Broadband Wireless Access (BWA) networks, we here propose spreading codes (Cumulative ACK (CA) code and ARQ Feedback Request (AFR) code) based reliable multicast feedback scheme. The status indications based on the automatic repeat request (ARQ) mechanism are needed in some multicast services. In accordance with various wireless channel environments, we demonstrate the performance excellency of our proposed scheme with respect to required uplink resources compared with the original feedback scheme based on unicast ARQ feedback messages. In addition, we analyze packet error rate (PER) against the various wireless channel environments.

Linear Network Coding in Convergecast of Wireless Sensor Networks: Friend or Foe?

Convergecast is probably the most common communication style in wireless sensor networks (WSNs). And linear network coding (LNC) is a promising concept to improve throughput or reliability of convergecast. Most of the existing works have mainly focused on exploiting these benefits without considering its potential adverse effect. In this paper, we argue that LNC may not always benefit convergecast. This viewpoint is discussed within four basic scenarios: LNC-aided and none-LNC convergecast schemes with and without automatic repeat request (ARQ) mechanisms. The most concerned performance metrics, including packet collection rate, energy consumption, energy consumption balance and end-to-end delay, are investigated. Theoretical analyses and simulation results show that the way LNC operates, i.e., conscious overhearing and the prerequisite of successfully decoding, could naturally diminish its advantages in convergecast. And LNC-aided convergecast schemes may even be inferior to none-LNC ones when the wireless link delivery ratio is high enough. The conclusion drawn in this paper casts a new light on how to effectively apply LNC to practical WSNs.

The combined automatic repeat request and rate control mechanism in S‐band mobile interactive multimedia asynchronous return link—design background, parameter dimensioning and first experimental results

SUMMARYIn the S‐band mobile interactive multimedia specification, an asynchronous access using Enhanced Spread Spectrum Aloha random access has been defined for occasional messaging applications. This access scheme is complemented by a combined automatic repeat request and terminal rate control mechanism that is described in this paper. Furthermore, a queuing theory‐based model is developed to describe the behaviour of the automatic repeat request mechanism, and performance results from the first proof‐of‐concept implementation are presented. Copyright © 2014 John Wiley & Sons, Ltd.

Low‐density parity‐check and fountain code performance over mobile wireless optical channels

ABSTRACTBy considering error control in different layers, the efficiency of several mechanisms is discussed in the context of wireless optical transmission of mobile health care application data. In this respect, we assume an emitter placed on a monitored patient and a fixed receiver. Because of patient mobility and health care data rate, the wireless optical channel is fading slowly. To ensure reliable communication, we study in the physical layer the low‐density parity‐check code performance by analysing the results in terms of outage probability. Concerning the application layer, we explore fountain codes, which are also known as Luby transform codes, together with an automatic repeat request mechanism by determining the related outage capacity. Taking into account the performance of both layers, we show that it is possible to design the physical layer code rate in that we maximise the effective data rate in the application layer. Moreover, we point out that Luby transform and low‐density parity‐check codes constitute an efficient and robust mechanism to reduce optical emitted power, which is of main concern for health care application. Copyright © 2014 John Wiley & Sons, Ltd.