On HARQ Schemes in Satellite-Terrestrial Transmissions

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.

We propose and analyze a scheme for wireless channels, which is a combination of a hybrid type I automatic repeat request (ARQ) scheme and a power ramping. In the hybrid type I ARQ scheme, the same redundancy bits for error correction is transmitted repeatedly when a negative acknowledgment (NAK) is obtained. In addition to the ARQ scheme, the power ramping is considered for more reliable downlink data transmission, in which the transmission power is gradually changed from a small level to large levels when the number of retransmission increases. This is done without any knowledge of the channels at the transmitter. Simulation results show that by applying the combined hybrid ARQ and power ramping scheme with properly selected parameters, it has a throughput advantage of 3-5%.

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 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.

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

It is generally impossible to avoid occurrences of errors of the data transmission because of the disturbing factors such as disconnections, noises or distortions in a communication line. Therefore, the error‐control procedure is indispensable to trnnsmit high‐quality data and its various techinques have been considered from the viewpoints of high reliability data transmission. the main techniques in the error‐correcting strategies are classified into the following three categories: (i) forward‐error‐correction (FEC) scheme; (ii) automatic‐repeat‐request (ARQ) scheme; and (iii) hybrid ARQ scheme. the hybrid ARQ scheme is the system combined FEC scheme with ARQ scheme. This aims to reduce the frequency of retransmissions as much as possible and to gain a constant data throughput, even in a worse communication environment, by coding error patterns that would be expected to occur frequently. However, when the first data of transmission has failed, the hybrid ARQ is removed to the ARQ policy with the same FEC, i.e., its data throughput decreases because of bit increments, such as codes to correct errors in the data transmission. This is called type‐I hybrid ARQ and its modified systems, which are called type‐II hybrid ARQ, have been studied and proposed by many authors. This paper suggests a new type‐II hybrid ARQ system from the viewpoint of improving the data throughput and derives the mean time to success of the data transmission. Then, the mean times of the system are compared analytically with those of the usual ARQ and the type‐I hybrid ARQ, and an evaluation is done.

We develop a general model based on random coding bounds to explain and predict the coding performance of various type-I and type-II hybrid automatic repeat request (HARQ) schemes based on the bit-interleaved coded modulation (BICM) in 3GPP HSPA. We explore how the intrinsic properties of BICM interact with various transmitter-side (e.g., whether to use the same bit mapping for retransmission) and receiver-side HARQ options (e.g., bit vs. symbol level processing and Log-MAP vs. Log-Max demodulation). The accuracy of the theoretical model is verified with extensive link simulations. The performance model can be incorporated into radio resource management algorithms for efficient wireless network operations. In a companion paper, the unified analytical model is further applied to investigate performance of LTE HARQ operations, which consist of varying mixture of type-I/II and bit remapping HARQ features.

The paper compares two hybrid automatic repeat request (HARQ) schemes using incremental redundancy (IR) which have been proposed for the UMTS (W-CDMA) high speed downlink shared channel (HS-DSCH). Their relative throughput performance is reported for various channel conditions. It is shown that the two-stage rate-matching scheme has marginally worse performance compared to the alternative block interleaving scheme for certain coding rates and under some channel conditions.

We propose a new data link control protocol for wireless ATM networks. This new protocol can support both real time and non-real-time services by adopting different error control mechanisms. For real-time traffic, only forward error control (FEC) is used for error correction. For non-real-time traffic, a hybrid automatic repeat request (ARQ) scheme is adopted to reduce the cell loss ratio to a minimum level. In both the FEC and hybrid ARQ schemes, the coding rate is adapted to the channel conditions. When the signal-to-noise ratio (SNR) is high, the coding rate may be higher; while when the channel is bad, the coding rate is adjusted to be lower. The automatic coding rate adaptiveness guarantees the high utilization of the scarce wireless channel resources.

A modified type of hybrid ARQ (HARQ) scheme with erasures correction (HARQ-EC) is considered. The performance of the proposed system has been analyzed under the assumption that the forward channel is memoryless and suffers from additive white Gaussian noise (AWGN) and Nakagami common distributed fading. A good agreement between the simulations' results and the theoretical ones was achieved. The examined HARQ-EC was compared with a well known HARQ system. The HARQ-EC system is characterized by significantly better throughput efficiency (TE) in a range of SNRs for approximately the same bit error rate (BER).

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.

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.

Automatic repeat request (ARQ) is a widely used technique in communication systems for transmission error control. In this paper, a Hybrid-ARQ (H-ARQ) scheme for LDPC coded system with low complexity and reduced additional transmission cost is proposed. This H-ARQ scheme exploit the unequal error protection (UEP) property in irregular LDPC coding and high-order quadrature amplitude modulation (QAM), where the bits with less protection are retransmitted with improved protection. Simulation results based on the power line communication (PLC) G.hn system demonstrate the advantage and flexibility of the proposed scheme over traditional H-ARQ scheme.

User scheduling and multiuser multi-antenna (MU-MIMO) transmission are at the\ncore of high rate data-oriented downlink schemes of the next-generation of\ncellular systems (e.g., LTE-Advanced). Scheduling selects groups of users\naccording to their channels vector directions and SINR levels. However, when\nscheduling is applied independently in each cell, the inter-cell interference\n(ICI) power at each user receiver is not known in advance since it changes at\neach new scheduling slot depending on the scheduling decisions of all\ninterfering base stations. In order to cope with this uncertainty, we consider\nthe joint operation of scheduling, MU-MIMO beamforming and Automatic Repeat\nreQuest (ARQ). We develop a game-theoretic framework for this problem and build\non stochastic optimization techniques in order to find optimal scheduling and\nARQ schemes. Particularizing our framework to the case of "outage service\nrates", we obtain a scheme based on adaptive variable-rate coding at the\nphysical layer, combined with ARQ at the Logical Link Control (ARQ-LLC). Then,\nwe present a novel scheme based on incremental redundancy Hybrid ARQ (HARQ)\nthat is able to achieve a throughput performance arbitrarily close to the\n"genie-aided service rates", with no need for a genie that provides\nnon-causally the ICI power levels. The novel HARQ scheme is both easier to\nimplement and superior in performance with respect to the conventional\ncombination of adaptive variable-rate coding and ARQ-LLC.\n