Marc Werner

Congestion control for vehicular safety: synchronous and asynchronous MAC algorithms

The IEEE 802.11p standard specifies the PHY and MAC layer operations for transmitting and receiving periodic broadcast messages for vehicular safety. Many studies have identified issues with the CSMA based IEEE 802.11p MAC at high densities of devices, mainly reflected by low packet reception rate. In this paper, we make an interesting observation that with increasing density, the IEEE 802.11p MAC tends towards an ALOHA-type behavior where concurrent transmissions by close-by devices are not prevented. This behavior can lead to poor packet reception rate even for vehicles in close neighborhood. Many efforts have been made to address the IEEE 802.11p MAC issues to provide better performance for DSRC safety applications, including the introduction of Decentralized Congestion Control (DCC) algorithm to ETSI standards in Europe. In this paper, we evaluate the performance of the proposed DCC algorithm and observe that the nominal parameters in DCC are unsuitable in many scenarios. Using transmit power control as an example, we develop a simple rule within the DCC framework that can significantly improve the safety packet reception performance with increasing densities. The DCC algorithms are fully compatible with the IEEE 802.11p standards and asynchronous in nature. A parallel approach to handle high device densities is a slotted synchronous MAC, where time is slotted based on GPS synchronization and each transmitter contends for a set of recurring time slots (or channels) with periodicity matching the required safety message periodicity. As compared to the per-packet based contention scheme as in CSMA defined in IEEE 802.11, such a scheme is much better suited for periodic safety broadcast. In this paper, we design a standard compliant TDM overlay on top of the MAC layer that can significantly improve the packet reception performance. Combined with a distributed resource selection protocol, the synchronous MAC can discover even more neighboring devices than the improved asynchronous approach, making DSRC safety applications more reliable.

The road to IMT-advanced communication systems: State-of-the- art and innovation areas addressed by the WINNER + project

Phases I and II of the WINNER project contributed to the development, integration, and assessment of new mobile network techniques from 2004 to 2007. Some of these techniques are now in the 3GPP LTE and IEEE 802.16 (WiMAX) standards, while others are under consideration for LTE-Advanced and 802.16m. The WINNER+ project continues this forwardlooking work for IMT-advanced technologies and their evolution, with a particular focus on 3GPP LTE-advanced. This article provides an overview of the WINNER system concept and several of its key innovative components.

Cellular In-Band Modem Solution for eCall Emergency Data Transmission

eCall is a project of the European Commission for the improvement of transportation safety by providing rapid assistance to motorists involved in a collision anywhere in the European Union. In the event of a collision, the intended solution employs an in-band modem that transmits vehicle location, airbag deployment, and other relevant information timely and reliably from the in-vehicle system (IVS) over the cellular network voice channel to the public safety answering point (PSAP). This paper describes the requirements, system design and performance of the eCall in-band modem solution that was selected by 3GPP. Due to the employment of this solution in life-critical situations, transmission reliability and speed are of utmost importance. The effective transmission channel is characterized by the highly nonlinear speech codec, as well as radio channel impairments, constituting a challenge for the in-band transmission of digital data. Several innovative transmission concepts were developed for our eCall in-band modem solution to address this challenge.

Cost Assessment and Optimization Methods for Multi-Node Radio Access Networks

The expected performance improvements of next-generation mobile radio access networks (RANs) can be achieved, e.g., by a flexible deployment of different types of radio access points (RAPs), such as intelligent relay nodes (RNs). To facilitate a cost-vs.-performance assessment of different deployment options, this paper presents a classification of different RAN cost components. Then, a method for deployment cost optimization is introduced which allows a comparison of the cost effectiveness of different RAN deployments by calculating optimum densities of different RAP types, based on a multi-dimensional iso-performance map. This method is first derived in theory and then demonstrated for two different deployment scenario examples.

IMT-Advanced and next-generation mobile networks [Guest Editorial]

Globally, mobile communications are moving toward broadband communication systems to meet the challenges of significantly increasing data traffic such as that for mobile Internet applications. In order to meet this increasing traffic, the International Telecommunication Union - Radiocommunication Standardization Sector (ITU-R) initiated in 2000 the process toward the next generation of International Mobile Telecommunications systems, referred to as IMT-Advanced systems.