Retransmission Latency Research Articles

Wireless Multi-Node uRLLc B5G/6G Networks for Critical Services in Electrical Power Systems

The successful operations of power system require the support of communication networks with massive nodes access and two-way reliable and latency-critical transmission, which is the most-important use case of ultra-reliable low-latency communications (uRLLc) in the Fifth-Generation and Beyond and Sixth-Generation (B5G/6G) networks. In this paper, based on the orthogonal frequency division multiplexing (OFDM) signal in 5G, a new OFDM employing the hopped subcarrier technique (OFDM/FH) is proposed to attain the multiple nodes connectivity and the enhancement of transmission reliability. Considering the short and bursty packet types in the control information of power systems, the OFDM/FH signal can be naturally integrated with the mini-slot frame structure and automatic repeat request (ARQ) scheduling scheme to reduce the latency. The trade-off between the reliability in terms of the bit-error rate (BER) and the retransmission latency is investigated by semi-analytic simulations. Through the new joint design of the signal waveform and frame structure for uRLLc, we find that the proposed system can attain up to 99.999% reliability and ms-level latency for electric power services, even in the harsh wireless environment.

Balancing Queueing and Retransmission: Latency-Optimal Massive MIMO Design

One fundamental challenge in 5G URLLC is how to optimize massive MIMO systems for achieving low latency and high reliability. A natural design choice to maximize reliability and minimize retransmission is to select the lowest allowed target error rate. However, the overall latency is the sum of queueing latency and retransmission latency, hence choosing the lowest target error rate does not always minimize the overall latency. In this paper, we minimize the overall latency by jointly designing the target error rate and transmission rate adaptation, which leads to a fundamental tradeoff point between queueing and retransmission latency. This design problem can be formulated as a Markov decision process, which is theoretically optimal, but its complexity is prohibitively high for real-system deployments. We managed to develop a low-complexity closed-form policy named Large-arraY Reliability and Rate Control (LYRRC), which is proven to be asymptotically latency-optimal as the number of antennas increases. In LYRRC, the transmission rate is twice of the arrival rate, and the target error rate is a function of the antenna number, arrival rate, and channel estimation error. With simulated and measured channels, our evaluations find LYRRC satisfies the latency and reliability requirements of URLLC in all the tested scenarios.

Detect Slitheen by analyzing the browsing behaviors and forcing retransmission

Previous studies on decoy routing did not consider the impact of content delivery networks (CDN). The CDN are widely used by popular websites which should not be ignored. In this paper, we take the first step to study the problem of applying the decoy routing in the CDN. In detail, we take Slitheen, which is one of the most advanced decoy routing techniques as our research object, and design the detection attacks from the following aspects: replacing the CDN edge servers; analyzing retransmission latency; comparing ciphertexts; analyzing the page loading duration. If Slitheen exposes its users to the censor, they will be in great danger in some repressive regimes. In order to reinforce Slitheen, we propose attack plans from the perspective of the attacker. To the best knowledge of the authors, our work is the first research on decoy routing in the CDN. By simulations, we demonstrate the feasibility of our detection scheme. We show that using our attack methods, the packet-sending frequency, the retransmission delay, and the page loading durations of Slitheen sessions are all obviously different from regular ones.

A Low-Latency Collaborative HARQ Scheme for Control/User-Plane Decoupled Railway Wireless Networks

The control/user (C/U) plane decoupled railway wireless network is an innovative architecture recently proposed to meet the communication demands of both train control systems and onboard passengers. The core idea is to completely separate the C-plane and the U-plane into different network nodes operating at different frequency bands. Although the system capacity of this network architecture can be highly increased, the forwarding latency of X3 interfaces to link the C-plane and the U-plane becomes a serious problem, particularly for hybrid automatic repeat request (HARQ) protocols that demand frequent interactions between the C-plane and the U-plane. To address this challenging problem, we propose a low-latency collaborative HARQ scheme in this paper. Specifically, we develop a new collaborative transmission framework where the possible spare resources on lower frequency bands of macrocells excluding those used by C-plane transmissions can be utilized to help small cells relay erroneously received data. Compared with the conventional HARQ scheme, the proposed scheme requires fewer retransmissions to reach the same transmission reliability, thereby mitigating the latency problem caused by HARQ retransmissions. Furthermore, channel mapping is also redesigned to conform to the proposed collaborative transmission framework. Through theoretical analysis, we derive the expression of the average number of retransmissions related to the sum of independent Gamma variables. Finally, the results of simulation experiments show that the proposed scheme can largely decrease the retransmission latency for railway wireless networks.

Fast Shared Feedback Methods for Uplink CoMP with H-ARQ

An efficient direct feedback method from coordinated base stations (BSs) to a mobile station (MS) for an uplink (UL) coordinated multipoint (CoMP) reception with supporting hybrid automatic-repeat-request (H-ARQ) transmission is proposed. Acknowledgement (ACK)/negative acknowledgement (NACK) feedback based on local detection at each BS in the CoMP set is directly transmitted from the BSs using shared-feedback resources. Therefore, an MS can obtain global ACK/NACK information without experiencing extra backhaul delay with a small feedback overhead, and we can reduce the H-ARQ retransmission latency for the inter-cell UL-CoMP operation. To minimize the ACK/NACK detection error at the MS, we investigate the optimized design methods for shared-feedback resources. We derived the analytical detection error probability of the proposed feedback method and the optimum sub-block size to minimize misdetection probability for a fixed overhead and false alarm rate. Based on the analytical and computer simulation results, we have verified that the proposed feedback method can provide a reliable detection performance with a small feedback overhead. In addition, system level simulation results show the proposed fast feedback based inter-cell UL-CoMP system increases the system throughput compared to the conventional intra-cell UL-CoMP without increasing the feedback latency.

Low‐latency retransmission control in a wireless communication system for plant instrumentation and control

AbstractWhen wireless communication technology is applied to plant instrumentation and control systems, it is important to ensure real‐time transmission and high reliability of the wireless communication system. However, the wireless communication system is prone to more frequent occurrence of transmission errors than a wired communication system, so that generally retransmission is implemented generically. To reduce retransmission latency, we propose a method of low‐latency retransmission control, which is a data block transmission method with multi‐redundant media access control layer (MAC) headers, to implement a wireless communication system for plant instrumentation and control. We carried out system tests using prototypes with the proposed methods, that is, data block transmission with multi‐redundant MAC headers. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Improving latency for interactive, thin-stream applications over reliable transport

A large number of network services use IP and reliable transport protocols. For applications with constant pressure of data, loss is handled satisfactorily, even if the application is latency sensitive. For applications with data streams consisting of intermittently sent small packets, however, users experience extreme latencies more frequently. Due to the fact that such thin-stream applications are commonly interactive and time-dependent, increased delay may severely reduce the experienced quality of the service. When TCP is used for thin-stream applications, events of highly increased latency are common, caused by the way retransmissions are handled. Other transport protocols that are deployed in the Internet, like SCTP, model their congestion control and reliability on TCP, as do many frameworks that provide reliability on top of unreliable transport. We have tested several application-and transport layer solutions, and based on our findings, we propose sender-side enhancements that reduce the application-layer latency in a manner that is compatible with unmodified receivers running commodity opeating systems like Linux, *BSD, Mac OSX and Windows. We have implemented the mechanisms as modifications to the Linux kernel, both for TCP and SCTP. The mechanisms are dynamically triggered so that they are only active when the kernel identifies the stream as thin. To evaluate the performance of our modifications, we have conducted a wide range of experiments using replayed thin-stream traces captured from real applications as well as artificially generated thin-stream data patterns. From the experiments, effects on latency, redundancy and fairness were evaluated. The analysis of the performed experiments shows great improvements in latency for thin streams when applying the modifications. Surveys where users evaluate their experience of several applications' quality using the modified transport mechanisms confirmed the improvements seen in the statistical analysis. The positive effects of our modifications were shown to be possible without notable effects on fairness for competing streams. We therefore conclude that it is advisable to handle thin streams separately, using our modifications, when transmitting over reliable protocols to reduce retransmission latency.

Improving Handover Quality in 4G Mobile Systems

In this paper, we propose a new handover algorithm to guarantee handover quality in 4G mobile systems. The proposed algorithm limits the handover interruption time by improving the HARQ retransmission latency of the first packet transmitted from new serving cell. Through the simulations, we proved that our algorithm meets the requirement of handover interruption time for TCP services with high rate.