Backlog and Delay Reasoning in HARQ Systems

Recently, hybrid-automatic-repeat-request (HARQ) systems have been favored in particular state-of-the-art communications systems since they provide the practicality of error detections and corrections aligned with repeat-requests when needed at receivers. The queueing characteristics of these systems have taken considerable focus since the current technology demands data transmissions with a minimum delay provisioning. In this paper, we investigate the effects of physical layer characteristics on data link layer performance in a general class of HARQ systems. Constructing a state transition model that combines queue activity at a transmitter and decoding efficiency at a receiver, we identify the probability of clearing the queue at the transmitter and the packet-loss probability at the receiver. We determine the effective capacity that yields the maximum feasible data arrival rate at the queue under quality-of-service constraints. In addition, we put forward non-asymptotic backlog and delay bounds. Finally, regarding three different HARQ protocols, namely Type-I HARQ, HARQ-chase combining (HARQ-CC) and HARQ-incremental redundancy (HARQ-IR), we show the superiority of HARQ-IR in delay robustness over the others. However, we further observe that the performance gap between HARQ-CC and HARQ-IR is quite negligible in certain cases. The novelty of our paper is a general cross-layer analysis of these systems, considering encoding/decoding in the physical layer and delay aspects in the data-link layer

Using Channel Output Feedback to Increase Throughput in Hybrid-ARQ

Hybrid-ARQ protocols have become common in many packet transmission systems due to their incorporation in various standards. Hybrid-ARQ combines the normal automatic repeat request (ARQ) method with error correction codes to increase reliability and throughput. In this paper, we look at improving upon this performance using feedback information from the receiver, in particular, using a powerful forward error correction (FEC) code in conjunction with a proposed linear feedback code for the Rayleigh block fading channels. The new hybrid-ARQ scheme is initially developed for full received packet feedback in a point-to-point link. It is then extended to various different multiple-antenna scenarios (MISO/MIMO) with varying amounts of packet feedback information. Simulations illustrate gains in throughput.Comment: 30 page

On the impact of link layer retransmission schemes on TCP over 4G satellite links

We study the impact of reliability mechanisms introduced at the link layer on the performance of transport protocols in the context of 4G satellite links. Specifically, we design a software module that performs realistic analysis of the network performance, by utilizing real physical layer traces of a 4G satellite service. Based on these traces, our software module produces equivalent link layer traces, as a function of the chosen link layer reliability mechanism. We further utilize the link layer traces within the ns-2 network simulator to evaluate the impact of link layer schemes on the performance of selected Transmission Control Protocol (TCP) variants. We consider erasure coding, selective-repeat automatic request (ARQ) and hybrid-ARQ link layer mechanisms, and TCP Cubic, Compound, Hybla, New Reno and Westwood. We show that, for all target TCP variants, when the throughput of the transport protocol is close to the channel capacity, using the ARQ mechanism is most beneficial for TCP performance improvement. In conditions where the physical channel error rate is high, hybrid-ARQ results in the best performance for all TCP variants considered, with up to 22% improvements compared to other schemes

Energy-efficient wireless communication

In this chapter we present an energy-efficient highly adaptive network interface architecture and a novel data link layer protocol for wireless networks that provides Quality of Service (QoS) support for diverse traffic types. Due to the dynamic nature of wireless networks, adaptations in bandwidth scheduling and error control are necessary to achieve energy efficiency and an acceptable quality of service. In our approach we apply adaptability through all layers of the protocol stack, and provide feedback to the applications. In this way the applications can adapt the data streams, and the network protocols can adapt the communication parameters

CLIFT: a Cross-Layer InFormation Tool for Latency Analysis Based on Real Satellite Physical Traces

New mobile technology generations succeed in achieving high goodput, which results in diverse applications profiles exploiting various resource providers (Wifi, 4G, 5G, . . . ). Badly set parameters on one of the network component may severely impact on the transmission delay and reduce the quality of experience. The cross layer impact should be investigated on to assess the origin of latency. To run cross-layer (from physical layer to application layers) simulations, two approaches are possible: (1) use physical layer models that may not be exhaustive enough to drive consistent analysis or (2) use real physical traces. Driving realistic measurements by using real physical (MAC/PHY) traces inside network simulations is a complex task. We propose to cope with this problem by introducing Cross Layer InFormation Tool (CLIFT), that translates real physical events from a given trace in order to be used inside a network simulator such as ns-2. Our proposal enables to accurately perform analysis of the impact of link layer reliability schemes (obtained by the use of real physical traces) on transport layer performance and on the latency. Such approach enables a better understanding of the interactions between the layers. The main objective of CLIFT is to let us study the protocols introduced at each layer of the OSI model and study their interaction. We detail the internal mechanisms and the benefits of this software with a running example on 4G satellite communications scenarios