Combining Hybrid Automatic Repeat Request Research Articles

Intelligent hybrid automatic repeat request retransmission for multi‐band Wi‐Fi networks

With the increase of Wi-Fi connections and throughput, the problems posed by unreliable connection and unstable delay need to be urgently solved through advanced methods. The IEEE 802.11ax standard was designed to improve the reliability of connection and increase the throughput in dense Wi-Fi scenario where the inter-site interference becomes more serious and the spectral resources are more insufficient. Furthermore, in the next generation of Wi-Fi standard IEEE 802.11be, the hybrid automatic repeat request (HARQ) and multi-band technologies will be introduced to solve the problems of unstable delay, serious interference and insufficient spectrum resources. In this paper, retransmission schemes combined multi-band and hybrid automatic repeat request are deeply studied to improve the retransmission efficiency. Combining hybrid automatic repeat request with multi-band, this paper proposes three kinds of retransmission mode: insisting on the current frequency band (ICFB) retransmission, switching to the backup frequency band (SBFB) retransmission and concurrent retransmitting on dual-band (CRDB). Then, an intelligent selection algorithm of retransmission mode based on machine learning is designed to determine the optimal mode. Theoretical analysis and experimental results show that the proposed method can greatly improve the retransmission efficiency and thereby reduce the transmission latency and increase the throughput for multi-band Wi-Fi networks.

Ultra Reliable Communication via Optimum Power Allocation for HARQ Retransmission Schemes

In this work, we develop low complexity, optimal power allocation algorithms that would allow ultra reliable operation at any outage probability target with minimum power consumption in the finite blocklength regime by utilizing Karush-Kuhn-Tucker (KKT) conditions. In our setup, we assume that the transmitter does not know the channel state information (CSI). First, we show that achieving a very low packet outage probability by using an open loop setup requires extremely high power consumption. Thus, we resort to retransmission schemes as a solution, namely Automatic Repeat Request (ARQ), Chase Combining Hybrid ARQ (CC-HARQ) and Incremental redundancy (IR) HARQ. Countrary to classical approaches, where it is optimal to allocate equal power with each transmission, we show that for operation in the ultra reliable regime (URR), the optimal strategy suggests transmission with incremental power in each round. Numerically, we evaluate the power gains of the proposed protocol. We show that the best power saving is given by IR-HARQ protocol. Further, we show that when compared to the one shot transmission, these protocols enable large average and maximum power gains. Finally, we show that the larger the number of transmissions is, the larger power gains will be attained.

Performance Analysis of Hybrid ARQ for Ultra-Reliable Low Latency Communications

Considering an ultra-reliable low latency communication scenario, we assess the trade-off in terms of energy consumption between achieving time diversity through retransmissions and having to communicate at a higher rate due to latency constraints. Our analysis considers Nakagami-m block-fading channels with Chase combining hybrid automatic repeat request. We derive a fixed-point equation to determine the best number of allowed transmission attempts considering the maximum possible energy spent, which yields insights into the system behavior. Furthermore, we compare the energy consumption of the proposed approach against direct transmission with frequency diversity. Results show substantial energy savings using retransmissions when selecting the maximum number of transmission attempts according to our approach. For instance, considering a Rayleigh channel and smart grid teleprotection applications, our approach uses around 8 times less energy per bit compared with a direct transmission with frequency diversity.

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.

Adaptive Modulation and Coding with Selective Retransmission under OFDM signaling

In this paper, we present bandwidth efficient selective retransmission method in conjunction with adaptive modulation and coding (AMC) scheme for OFDM waveform. In the proposed method, when a packet failure occurs, receiver requests retransmission of information symbols prone to error corresponding to the low signal-to-noise ratio (SNR) sub-carriers of OFDM modulation. The selective retransmission avoids unnecessary retransmission and AMC chooses a proper modulation and coding scheme with an objective to maximize the throughput. Our method achieves higher throughput as compared to conventional retransmission methods such as Chase combining hybrid automatic repeat reQuest (CC-HARQ) and incremental redundancy hybrid automatic repeat reQuest (IR-HARQ). We also provide the throughput and delay analysis of the proposed method for non-truncated ARQ. The simulation results demonstrate throughput gain without significant impact on delay as compared to the conventional retransmission approaches.

Optimising energy efficiency of LDPC coded chase combining HARQ system

The energy efficiency of the low-density parity check (LDPC) coded chase combining hybrid automatic repeat request (HARQ) system over the additive white Gaussian noise channel is analysed. The energy efficiency can be improved by increasing the maximum transmission number (K) and reducing the transmit power. The asymptotic energy efficiency corresponding to K = ∞ equals the reciprocal of the threshold signal-to-noise ratio of the forward error correction code, which does not depend on the falling speed of the word error ratio. When the retransmission number is relatively small, optimising equal transmit power and variable transmit power can improve the energy efficiency by up to 10 and 18% respectively, compared with minimum equal power transmission.

A Semianalytical Performance Prediction Method for an Iterative MIMO MMSE Receiver With Forward and Backward Error Control

This paper proposes a semianalytical performance prediction method for an iterative receiver that processes signals arriving through a frequency-selective multiple-input multiple-output radio channel. Earlier results provide a distribution of the signal-to-interference-plus-noise ratio at the output of a frequency domain soft interference cancellation minimum mean square error equalizer, which is used to approximate the distribution of the log-likelihood ratios (LLRs) of the demapped bits. Mutual information transfer charts establish a bijective relationship between the variance of the LLRs and the mutual information. We assume a 3rd Generation Partnership Project compliant turbo code, whose transfer charts are simulated in advance. By approximating the LLR variance distribution of the demapped equalizer output, we can evaluate the probability of an intersection between an equalizer chart associated with a random channel realization and a fixed decoder chart. This probability provides the frame error rate. Our proposed prediction method allows horizontally and vertically encoded spatial multiplexing schemes. The vertically encoded scheme is complemented by the inclusion of the Chase combining hybrid automatic repeat request protocol. The proposed method allows reasonable receive antenna correlation.

Analysis of Plain and Diversity Combining Hybrid ARQ Protocols Over the $m(\geq 2)$-Ary Asymmetric Channel

In the automatic repeat request (ARQ) protocol, the sender keeps retransmitting a code word until it receives a positive acknowledgment from the receiver sent through the feedback channel. This correspondence proposes plain and diversity combining hybrid ARQ protocol communication schemes suitable for the m(ges2)-ary asymmetric channel using t-asymmetric error correcting/all asymmetric error detecting (t-AEC/AAED) codes. The analysis shows that error correction definitely improves the throughput of the system compared to the ARQ protocol which uses only error detecting codes. The correspondence provides simple analytic expressions for the average number of transmissions of a code word in both plain and diversity combining t-AEC/AAED ARQ (tges0) protocol systems over the m-ary asymmetric channel, mges2. An example is shown on how to get very close to the Z-channel capacity