Andrea Vesco

An insight into Decentralized Congestion Control techniques for VANETs from ETSI TS 102 687 V1.1.1

Many cooperative applications designed to improve road safety rely on the frequent exchange of awareness messages among vehicles. Therefore, under high vehicle density, the channel medium is expected to get congested. To tackle this situation, the European Telecommunications Standards Institute (ETSI) specified a set of Decentralized Congestion Control (DCC) mechanisms that adapt the transmission parameters based on channel load measures. Due to some concerns about its effectiveness and stability, DCC and its overall philosophy are currently being revised and extended: all in all, DCC deserves additional investigations. For this purpose, in this paper a simulation analysis is presented, aiming at enriching the insight into the DCC behaviour, under a variety of channel load conditions and through the definition of both link- and application-layer performance metrics. Achieved results show that the DCC techniques are not really effective with the currently specified parameters settings; hence some hints are given to improve their performance.

Quality-Oriented Video Transmission With Pipeline Forwarding

This work proposes a quality-oriented multimedia delivery framework that tackles the issue of optimizing video broadcasting and interactive video applications over packet networks with respect to both resource utilization and user perceived quality. Previous work showed that the quality of service requirements of multimedia applications can be optimally satisfied by pipeline forwarding of packets by keeping delay controlled and resource utilization high, while enabling highly scalable network devices. These properties are key in today networks to enable valuable (i.e., chargeable for) services and to avoid that the traffic increase due to broadband video either collapses existing networks or forces the deployment of high cost, cutting-edge technology to properly upgrade them. However, the current Internet is not based on such technology and its incremental introduction raises questions on how to handle video packets generated by pipeline-forwarding-unaware sources. This work proposes to use the perceptual importance of the carried video samples to determine which packets shall be transferred with pipeline forwarding-thus receiving deterministic service-and which with a traditional, e.g., best effort or differentiated service. Two new scheduling algorithms are proposed, with an extensive analysis and simulation results, which also investigate the impact of the encoding scheme. Performance bounds have been established by comparing the proposed algorithms with an exhaustive-search approach, showing that the performance is within 2 dB PSNR from the optimal solution in the worst case.

An Analytical Packet Error Rate Model for WAVE Receivers

Vehicular Ad-Hoc Networks (VANETs) have been extensively studied in the last years. Despite the availability of IEEE 802.11p transceivers, most of the literature presents simulation results, rather than real-world measurements. This is mainly due to the capability of simulations to facilitate interpretations of results; in fact any event can be decomposed into basic sub-events and the related causes analyzed in depth. However, this requires realistic settings of simulations to lead to consistent conclusions. Nowadays, most of the network simulators neglect the probabilistic nature of the decoding process at the receiver and this may have significant impact on the results. This paper is meant to fill this gap by proposing an analytical Packet Error Rate (PER) model for 802.11preceivers, particularly suitable for the implementation within packet-level simulators. It is completely parameterized as a stochastic function of line-rate, Signal to Noise ratio (SNR) and packet length, and it is consistent with experimental measurements.

The Bologna Ringway Dataset: Improving Road Network Conversion in SUMO and Validating Urban Mobility via Navigation Services

The current lack of reference datasets of road traffic mobility for network simulation jeopardizes the reliability and reproducibility of vehicular networking research. We contribute to the ongoing effort to develop dependable and publicly available mobility traces through the following: (1) implementing an original version of the Simulation of Urban Mobility (SUMO) road network conversion tool that allows importing OpenStreetMap (OSM) data in a neat automated fashion; (2) generating an original dataset of road traffic in Bologna, Italy; and (3) providing a novel validation methodology that builds on open data provided by navigation service, which we leverage to assess the quality of the proposed Bologna dataset. These three contributions are expected to benefit the whole research community, since they not only provide a new ready-to-use realistic dataset that can be input to network simulators but ease the generation and validation of further vehicular mobility traces for networking research as well.

A distributed bandwidth management scheme for multi-hop wireless access networks

A synchronous distributed coordination function called Time-Division Unbalanced Carrier Sense Multiple Access (TD-uCSMA) has been proposed to provide CSMA/CA with a mechanism for bandwidth management over single-hop wireless networks. TD-uCSMA relies on synchronization among nodes and the time-driven switching of Enhanced Distributed Channel Access (EDCA) parameters inside nodes. The solution, currently assessed in single-hop scenarios with CBR traffic profiles, is here validated on multi-hop scenarios and generalized to support heterogeneous traffic aggregates. This requires the definition of a bandwidth reservation model able to manage traffic aggregates with variable bit-rate and packet length. Notably the devised model shows a first order dependence only on bit-rate and on packet length statistics (mean and variance) due to a straight-forward consequence of the TD-uCSMA operating principles. Simulations validate this simple bandwidth reservation model and show its effectiveness over multi-hop wireless access networks.

Time-division access priority in CSMA/CA

This paper proposes TD-uCSMA a synchronous distributed coordination function which is meant to provide CSMA/CA with a mechanism for QoS provisioning and bandwidth management over WiFi networks. TD-uCSMA relies on synchronization among nodes and the time-driven switching of contention parameters inside nodes. The TD-uCSMA operating principles and preliminary synchronization issues are presented here together with an extensive simulation analysis showing the effectiveness of the proposed solution.

Optimized H.264 Video Encoding and Packetization for Video Transmission Over Pipeline Forwarding Networks

Previous works showed that the quality-of-service (QoS) requirements of multimedia applications can be optimally satisfied by pipeline forwarding (PF) by providing end-to-end delay guarantees as well as high network resource utilization. However, the unavoidable mismatch between reserved resources and the unpredictable traffic profile of a video stream has an impact on the resulting application layer quality. Therefore, a new low-complexity H.264 video encoding and packetization scheme based on a distortion-optimized macroblock grouping technique is designed here to maximize the performance of video transmission on PF networks. The scheme considers the perceptual importance of the different parts of the video data to group the most important information in few packets that are the natural candidates to receive the deterministic service provided by PF. Results show peak signal-to-noise ratio (PSNR) gains up to 2.5 dB over traditional video encoding and packetization schemes, as well as more graceful degradation in case of high network load.

Investigating the effectiveness of decentralized congestion control in vehicular networks

Vehicular ad hoc networks are expected to suffer from channel congestion, due to the high number of vehicles moving on the roads, the limited available bandwidth and the many applications that they will support. In order to mitigate such problem, ETSI has recently specified the Decentralized Congestion Control (DCC) mechanisms for Intelligent Transportation Systems (ITS) operating in the 5 GHz range. Although they are already part of the standard, very few results exist on the DCC performance. In this work, we aim at filling this gap by investigating the impact on the system performance of the single DCC mechanisms, as well as their joint effect when they are all implemented at the DCC access layer. Surprisingly, we find that DCC has little impact, and, in certain scenarios, it may even lead to performance degradation with respect to the case where the legacy IEEE 802.11p MAC protocol is implemented.

MAC layer impact on the performance of real-time cooperative positioning

This work analyzes the impact of medium access control (MAC) layer on the performance of real-time cooperative positioning in ad-hoc mobile wireless networks. The probability mass function (pmf) of the latency introduced by the MAC layer is here derived to assess the influence of MAC parameters on the latency and then operate on those to improve the positioning performance while reducing the number of position estimation iterations.

Advances on Time-Division Unbalanced Carrier Sense Multiple Access

Time-Division Unbalanced Carrier Sense Multiple Access (TDuCSMA) is a distributed MAC discipline compliant to the IEEE 802.11 standard that supports resource management and Quality of Service provisioning in Wi-Fi networks. This paper further highlights the compliance of TDuCSMA with IEEE 802.11 standard by suggesting the coexistence of TDuCSMA and CSMA/CA entities within the same node. The resulting distributed network functionalities are described by an analytical models which are also validated by simulations. The proposed models are meant to support network and service designs.