Design and Implementation of an Adaptive Algorithm for Hybrid Automatic Repeat Request

Since wireless channel is always band-limited with multi-path fading and highly burst errors, flexible error control is needed in wireless asynchronous transfer mode (WATM) networks. This paper proposes a hybrid automatic repeat request (HARQ) architecture which has on-demand quality of services (QoS). By choosing different options in the architecture, we get different error control schemes. In this paper, we investigate the performance of three different error control schemes, namely HARQ, HARQ with different redundancy, and adaptive HARQ with traffic-type-dependent redundancy. The simulation results show that the HARQ with FEC adaptation offers the best performance.

In comparison to Ultra-Reliable Low-Latency Communications (URLLC) in 5G mobile communication systems, the next generation URLLC (xURLLC) requires even lower latency and higher reliability. To address these requirements, we propose a novel redundancy version (RV)-adaptive hybrid automatic repeat request (HARQ) scheme. Our approach builds upon the existing 5G HARQ framework and 5G low-density parity-check (LDPC) codes, introducing an adaptive selection of the RV for the subsequent transmission based on the current decoding states. To determine the optimal RV, we use a modified version of the reciprocal channel approximation (RCA) algorithm to compare the decoding thresholds of all available RVs and select the one with the lowest threshold to maximize the likelihood of successful decoding. To further reduce processing delay, we apply a deep neural network (DNN) to predict the optimal RV for the next transmission. This prediction is made prior to the decoding process, ensuring that no additional delay is introduced. Since the selection is made before the decoding starts, our proposed method can seamlessly integrate with other adaptive-HARQ and fast HARQ schemes.

Hybrid automatic repeat request (HARQ) can make efficient and reliable transmission possible for radio communications. However, in the HARQ scheme, packet control information (PCI), such as HARQ block identifiers (HARQ block ids) in selective repeat ARQ (SR-ARQ), are required and the reduction of PCI overhead is an issue. In particular, type-II HARQ handles a large amount of PCI because it includes the HARQ block ids and sub-block ids. The sub-block id identifies the set of parity bits in the HARQ block of the corresponding sub-block, and is used to combine the sub-blocks. This report proposes a method of PCI reduction suitable for type-II HARQ with SR-ARQ. The method can inform the HARQ block id and sub-block id of each HARQ block by sending only the information on how many HARQ blocks are contained in each 1st, 2nd, 3rd, and 4th transmission group. The estimated size of reduced PCI and simulation results of our TDD communication system confirms that the proposed method greatly reduces PCI and improves data throughput compared to a conventional method.

We consider a novel mechanism to pool HARQ (Hybrid Automatic Repeat Request) memory at the UE (User Equipment). In legacy systems, each carrier is allocated a separate section of the total HARQ memory. By pooling this memory and allocating as HARQ requests arrive, we significantly improve the memory utilization. Moreover, we can accommodate a larger fraction of arriving HARQ requests thus increasing HARQ throughput without increasing buffer requirement at the UE. In this work, we model the HARQ memory system as a multiserver queue, and obtain expressions for dropping probability and memory occupancy. We compare the pooling system to the legacy technology in an asymptotic regime, which is a good approximation in cases where the ratio of the largest to smallest packet size is large. This regime holds for scenarios with large Transport Block sizes, such as 5G New Radio. In this regime, under large load factor, we show that blocking probability reduces under the pooling mechanism and uses less resources.

In this research work, the authors propose an error constrained data transmission approach using non-orthogonal multiple access (NOMA) protocol with hybrid automatic repeat request (HARQ) and different packet combining schemes. In this proposed work, the transmitter simultaneously transmits two data packets to the users (UEs) by considering the superposition coding technique in the power domain. The decoding scheme of the receiver changes according to the message decoding status in the previous rounds. This combined protocol has the capability of realizing ultra-reliability, error correction power in high error prone wireless links. The receiver adopts successive interference cancelation (SIC) to decode its own packet. Retransmission process is performed when the data is erroneously received by the destination and the receiver corrects the error by applying HARQ with Packet Combining (HARQ-PC) and HARQ with Aggressive Packet Combining (HARQ-APC) schemes. This paper analyzes the data rates, outage probabilities and bit error rates of UEs for downlink NOMA systems with respect to the transmit power using some basic parameters. The proposed schemes can greatly outperform the conventional NOMA with HARQ (NOMA-HARQ) in terms of data rates, outage probability and bit error rate in dynamic wireless channels.

This paper investigates reliable and secure transmissions over the Gaussian wiretap channel. A physical layer coding scheme based on Low-Density-Parity-Check (LDPC) codes with granular Hybrid Automatic Repeat reQuest(HARQ) protocol is presented. HARQ granularity aims at sending coded data at the minimum rate required for legitimate successful decoding while minimizing the information leakage that may benefit to eavesdropping. It will be shown that the granularity increases the frame error rate at the eavesdropping receiver. Since the secrecy level can be assessed through the bit error rate (BER) at the unintended receiver, intraframe and interframe error contaminations are employed to convert the loss of only few packets in the wiretap channel into much higher BERs at the eavesdropper. From the BERs at the legitimate and illegitimate receivers, the reliability and security regions can be determined. It is observed that with granular HARQ and interframe error contamination, signal to noise (SNR) regions that are simultaneously reliable and secure are expanded significantly.

In many wireless data systems, automatic repeat request (ARQ) and hybrid automatic repeat request (HARQ) work independently. In this paper, we introduce a new ARQ feedback scheme called Cross-Layer ARQ (CL-ARQ), where ARQ closely interoperates with HARQ by making use of the acknowledgement of HARQ internally. By doing so, CL-ARQ not only removes the overhead for ARQ acknowledgement messages, but also improves the average delivery delay and TCP throughput. Especially, when the entities in charge of HARQ and ARQ are located far apart geographically, CL-ARQ remarkably outperforms the legacy scheme.

본 논문은 type I 혼합-자동 반복 요구 (hybrid automatic repeat request: H-ARQ) 시스템에서 저밀도 패리티검사 (low-density parity-check: LDPC)로 부호화된 직교 주파수 분할 다중화 (orthogonal frequency division multiplexing: OFDM) 서브프레임의 전송 순서를 균등 결합 전력이 할당되도록 조정한 재전송 방법을 기초로 성능 개선을 채널 용량을 사용하여 분석하고, 계층 복호 방법을 적용하여 H-ARQ 재전송 기법의 수렴 속도 개선을 확인한다. 구체적으로 임의의 서브프레임 재전송 패턴에 대하여 채널 용량이 클수록 비트오류율 (bit error rate: BER) 성능도 우수하다는 사실을 검증한다. 그러므로 각 서브프레임에 대하여 균등 결합 전력 할당을 보장하는 서브프레임 재전송 패턴은 채널 용량을 최대로 하며, 임의의 다른 서브프레임 전송 순서 조정을 통한 재전송 패턴보다 성능이 우수하다. 결국 균등 결합 전력 할당을 만족하도록 서브프레임 순서를 조정하는 재전송 방법은 기존 체이스 결합 (Chase combining)보다 복호 복잡도를 증가시키지 않으면서도 주목할 만한 성능 개선을 보인다. In this paper, we introduce the low-density parity-check (LDPC) coded orthogonal frequency division multiplexing (OFDM) subframe reordering scheme for achieving equal combined power allocation in type I hybrid automatic repeat request (H-ARQ) systems and analyze the performance improvement by using the channel capacity. Also, it is confirmed that the layered decoding for subframe reordering scheme in H-ARQ systems gives faster convergence speed. It is verified from numerical analysis that a subframe reordering pattern having larger channel capacity shows better bit error rate (BER) performance. Therefore the subframe reordering pattern achieving equal combined power allocation for each subframe maximizes the channel capacity and outperforms other subframe reordering patterns. Also, it is shown that the subframe reordering scheme for achieving equal combined power allocation gives better performance than the conventional Chase combining scheme without increasing the decoding complexity.

There are two kinds of technique used for error control: FEC (forward error correction) and ARQ (automatic repeat request). Combining these two schemes, which is called HARQ (hybrid ARQ), makes it possible to increase the channel throughput. The error of the channel quality estimate that is used to select the MCS (modulation coding scheme) in type I HARQ can be a serious problem in scenarios when the mobile station moves at high speeds. Furthermore, in a system dominated by packet services, the interference level may be bursty, and thus it is difficult to predict the interference level. Therefore, the type II HARQ scheme is a more robust solution compared with type I HARQ. In order to improve channel throughput while at the same time satisfying quality of service (QoS) under various channel conditions, an efficient hybrid ARQ type II scheme is proposed. The optimum redundancy size for every transmission is calculated to maximize the throughput using QoS parameters, the performance of LDPC code and channel conditions. The proposed scheme, together with such benefits as QoS support, provides a way of achieving higher throughput in wireless communication systems.

A new hybrid automatic repeat request (HARQ) scheme is proposed for multiple-input multiple-output (MIMO) systems when the acknowledgment (ACK) bundling is applied for packet retransmissions. In the proposed HARQ scheme, both Chase combining (CC) and incremental redundancy (IR) are utilised for a retransmission request, and the proposed HARQ scheme is called a multiple retransmission strategy-based HARQ (MRS-HARQ). During the reception process of the MRS-HARQ, IR packets obtain signal-to-noise ratio gains using the extended detection with CC packets and the improved IR packets are utilised to eliminate the interference from the CC packets. This sequential reliability improvement allows the MRS-HARQ to decrease the occurrence of the deficient transmissions, and the proposed MRS-HARQ can achieve an improved error performance and throughput over the conventional CC-based and IR-based HARQ schemes with the ACK bundling.

In this paper, we propose a data-driven joint modulator and demodulator based on meta-learning for hybrid automatic repeat request (HARQ) schemes, which include Type-I HARQ, HARQ with chase combining (HARQ-CC), and HARQ with incremental redundancy (HARQ-IR). Data-driven deep learning (DL) techniques have proven particularly effective for enabling wireless systems to adapt to complex scenarios with unknown or imperfect channel conditions that are difficult to characterize analytically. Most existing DL approaches to realize data-driven communication frameworks are based on joint source-channel coding (JSCC). However, the difficulty in detecting transmission errors makes JSCC unsuitable for HARQ systems. To address this limitation, we propose a novel architecture that combines classical channel coding with DLbased modulation and demodulation. Specifically, we employ an autoencoder to implement both the modulator and demodulator. To quickly adapt to time-varying fading channels, the ModelAgnostic Meta-Learning (MAML) algorithm is leveraged to accelerate the convergence of the model as well as enhance the reliability of HARQ. The MAML framework is divided into two phases, including the pre-training phase to acquire shared initialization parameters across various channel conditions and the fine-tuning phase to rapidly adapt to specific channel states. Simulation results demonstrate that the proposed architecture offers dramatic improvements in convergence speed and generalization capabilities, and meanwhile boosts the reliability of HARQ schemes.

Emerging low date-rate Machine-to-Machine (M2M) communications call for promising Hybrid Automatic Repeat-reQuest (HARQ) schemes with improved link reliability and feedback efficiency. This motivates us to develop a novel adaptive HARQ scheme by exploiting the knowledge of Channel Quality Information (CQI), which can be obtained through either channel estimation techniques or location- aided technology. The proposed adaptive HARQ scheme will determine the suitable transmission mode to guarantee a specific Frame Error Rate (FER) during the first transmission with the aid of location information. Simulation results demonstrated that our proposed scheme can achieve more attractive throughput performance, while maintaining a similar FER, compared to conventional HARQ schemes.

In this paper, we propose a cross-layer design which combines adaptive modulation and coding (AMC) at the physical layer with a hybrid automatic repeat request (HARQ) protocol at the data link layer to minimize the packet error rate (PER) and maximize the spectral efficiency. By using Markov model to predict the channel condition of next frame according to the second order statistics characteristics of the former frame, we calculate the conditional probability density function and joint probability density function of signal to noise ratio (SNR). Further, we derive the packet error rate and average spectral efficiency in closed-form for transmission over Nakagami-m fading channels. Numerical results show that the proposed scheme can obtain lower PER and higher spectral efficiency c ompared with traditional HARQ protocol s. The cross-layer design scheme combing type-III HARQ with AMC can achieve the highest spectral efficiency and the lowest PER than type-I HARQ and type-II HARQ.

Existing hybrid automatic repeat request (HARQ) schemes are mainly designed at bit-level, in which the bits with lower reliability are re-encoded and then re-transmitted. However, this may lead to complicated and nonflexible bit-wise joint design among all the re-transmitted packets and introduce extra decoding latency. In this paper, we propose a novel HARQ scheme with multi-packet retransmission and packet-wise polarization, MPPP-HARQ, which simply retransmits the polar coded version of the failed packets as well as the new information packets instead of any specific part of them, so as to avoid all complicated and trivial inner-bit manipulation and greatly reduce the system complexity. Just like the bit-wise polarization, the packet-wise polarization is realized by proper modulo two addition among packets. By proper combination of multiple packets at each retransmission, we can reliably recover all the received packets at the decoder using a joint iterative decoding algorithm. Simulation results show that compared to the traditional HARQ protocol, MPPP-HARQ achieves superior performance and obtains a significant performance gain in terms of throughput and error rate. Index Terms-Polar code, HARQ, joint iterative decoding algorithm, packet-wise polarization

In 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.