Katrin Sjöberg

A Measurement Based Shadow Fading Model for Vehicle-to-Vehicle Network Simulations

The Vehicle-to-Vehicle (V2V) propagation channel has significant implications on the design and performance of novel communication protocols for Vehicular Ad Hoc Networks (VANET). Extensive research efforts have been made to develop and implement V2V channel models for advanced VANET system simulators. The impact of shadowing caused by other vehicles has, however, largely been neglected in most of the models, as well as in the system simulations. In this paper we present a simple shadow fading model targeting system simulations based on real world measurements performed in urban and highway scenarios. Video information from the measurements is used to separate the line-of-sight (LOS) condition from the obstructed line-of-sight (OLOS) by vehicles and non line-of-sight (NLOS) by buildings. It is observed that the vehicles obstructing LOS induce an additional attenuation of about

How Severe Is the Hidden Terminal Problem in VANETs When Using CSMA and STDMA

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Delay and interference comparison of CSMA and self-organizing TDMA when used in VANETs

\,dB in the received signal power. We use a Markov chain based state transition diagram to model transitions from LOS to obstructed LOS and present an example of state transition intensities for a real traffic mobility model. We also provide a simple recipe, how to incorporate our shadow fading model in VANET network simulators. (Less)

Comparing LIMERIC and DCC approaches for VANET channel congestion control

The hidden terminal problem is often said to be the major limiting performance factor in vehicular ad hoc networks. In this article we propose a definition of the hidden terminal problem suitable for broadcast transmissions and proceed with a case study to find how the packet reception probability is affected by the presence of hidden terminals. Two different medium access control methods; carrier sense multiple access (CSMA) from IEEE 802.11p and self-organizing time division multiple access (STDMA), are subject of investigation through computer simulations of a highway scenario with a Nakagami fading channel model. The results reveal that the presence of hidden terminals does not significantly affect the performance of the two MAC protocols. STDMA shows a higher packet reception probability for all settings due to the synchronized packet transmissions.

Live video streaming in IEEE 802.11p vehicular networks : Demonstration of an automotive surveillance application

IEEE 802.11p is the proposed wireless technology for communication between vehicles in a vehicular ad hoc network (VANET) aiming to increase road traffic safety. In a VANET, the network topology is constantly changing, which requires distributed self-organizing medium access control (MAC) algorithms, but more importantly the number of participating nodes cannot be restricted. This means that MAC algorithms with good scalability are needed, which can fulfill the concurrent requirements on delay and reliability from road traffic safety applications. The MAC method of IEEE 802.11p is a carrier sense multiple access (CSMA) scheme, which scales badly in terms of providing timely channel access for a high number of participating nodes. We therefore propose using another MAC method: self-organizing time division multiple access (STDMA) with which all nodes achieve timely channel access regardless of the number of participating nodes. We evaluate the performance of the two MAC methods in terms of the MAC-to-MAC delay, a measure which captures both the reliability and the delay of the delivered data traffic for a varying number of vehicles. The numerical results reveal that STDMA can support almost error-free transmission with a 100 ms deadline to all receivers within 100 m, while CSMA suffers from packet errors. Moreover, for all considered cases, STDMA offers better reliability than CSMA.

Capacity limitations in wireless sensor networks

Channel congestion is one of the major challenges for IEEE 802.11p-based vehicular ad hoc networks. Unless controlled, congestion increases with vehicle density, leading to high packet loss and degraded safety application performance. In this paper, we study two classes of congestion control - reactive and adaptive. The reactive approach is represented by the Decentralized Congestion Control (DCC) framework defined in ETSI. The adaptive approach is represented by the LIMERIC linear control algorithm. Both approaches control safety message transmission as a function of channel load (i.e. Channel Busy Ratio, CBR). A reactive approach uses CBR directly, defining an appropriate transmission behavior for each CBR value, e.g. via a table lookup. By contrast, an adaptive approach identifies the transmission behavior that drives CBR to a target channel load, thus achieving the best message throughput possible for any given vehicle density. The paper considers two variations of DCC, one in which it serves as a traffic shaping “gatekeeper” above the MAC sublayer, and another in which it additionally limits safety message generation at the facilities layer. The paper has two main results. First, it is shown that LIMERIC generally outperforms both DCC variations in a winding road scenario with various vehicle densities. Inter-packet reception gap and position tracking error are the primary metrics. This advantage is due to primarily LIMERICs ability to achieve a target load consistent with maximum throughput and vehicle awareness. Second, it is shown that both DCC variations are subject to steady state oscillations, and the case in which DCC also limits message generation is subject to truly unstable variations. The paper uses NS-2 simulation results to support these conclusions.

Cooperative Intelligent Transport Systems in Europe: Current Deployment Status and Outlook

Prospective IEEE 802.11p-enabled automotive video applications are identified. Preliminary experimental results of inter-vehicular live video streaming for surveillance applications are presented. A test-bed for the demonstration of the achievable visual quality under different channel conditions is described.

Stability Challenges and Enhancements for Vehicular Channel Congestion Control Approaches

It is expected that wireless sensor network will be used in home automation and industrial manufacturing in the future. The main driving forces for wireless sensor networks are fault tolerance, energy gain and spatial capacity gain. Unfortunately, an often forgotten issue is the capacity limits that the network topology of a wireless sensor network represents. In this paper we identify gains, losses and limitations in a wireless sensor network, using a simplified theoretical network model. Especially, we want to point out the stringent capacity limitations that this simplified network model provide. Where a comparison between the locality of the performed information exchange and the average capacity available for each node is the main contribution.

Performance evaluation of a mixed vehicular network with CAM-DCC and LIMERIC vehicles

The cooperative intelligent transport system (C-ITS) (also known as connected vehicle technology in the United States) is an application using vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications, at a carrier frequency of 5.9 GHz, to increase road traffic safety and efficiency in Europe. In this article, we hope to shed light on the current status of the C-ITS in Europe and the activities that must be accomplished before deployment can commence in 2019, the date announced by the CAR-2-CAR Communication Consortium (C2C-CC). There is immense activity regarding the launch of the C-ITS in Europe, and the automotive industry is also currently planning for the future.

Vehicle-to-Vehicle Communications

Channel congestion is one of the major challenges for IEEE 802.11p-based vehicular networks. Unless controlled, congestion increases with vehicle density, leading to high packet loss and degraded safety application performance. We study two classes of congestion control algorithms, i.e., reactive state-based and linear adaptive. In this paper, the reactive state-based approach is represented by the decentralized congestion control framework defined in the European Telecommunications Standards Institute. The linear adaptive approach is represented by the LInear MEssage Rate Integrated Control (LIMERIC) algorithm. Both approaches control safety message transmissions as a function of channel load [i.e., channel busy percentage (CBP)]. A reactive state-based approach uses CBP directly, defining an appropriate transmission behavior for each CBP value, e.g., via a table lookup. By contrast, a linear adaptive approach identifies the transmission behavior that drives CBP toward a target channel load. Little is known about the relative performance of these approaches and any existing comparison is limited by incomplete implementations or stability anomalies. To address this, this paper makes three main contributions. First, we study and compare the two aforementioned approaches in terms of channel stability and show that the reactive state-based approach can be subject to major oscillation. Second, we identify the root causes and introduce stable reactive algorithms. Finally, we compare the performance of the stable reactive approach with the linear adaptive approach and the legacy IEEE 802.11p. It is shown that the linear adaptive approach still achieves a higher message throughput for any given vehicle density for the defined performance metrics.