Cooperative safety applications require dedicated short-range communications (DSRC) to provide position-awareness of neighboring vehicles at a specific level of reliability, i.e., awareness-quality, up to a given distance, i.e., awareness-range. However, heavy communication loads negatively impact such awareness requirements due to communication impairments, ranging from strict capacity limitations of DSRC channels to correlated packet collisions due to periodic communication patterns. Transmission control strategies may adapt power or rate to control such impairments but risk missing the requirements of cooperative safety applications. In this paper, we design a new awareness control strategy by implementing a spatial awareness framework. Specifically, we adapt the distribution of the awareness-quality as a function of the awareness-range. Therefore, we first propose random transmit power control (RTPC), which manages to provide different levels of awareness-quality at different ranges, while mitigating correlated packet collisions by randomizing them in space. As RTPC is able to reduce the channel load, we secondly propose to combine RTPC with transmit rate control (TRC) and to benefit from the gained channel resources by subsequently increasing the update-rate and by implication, the quality of position-awareness. The spatial awareness control capability of RTPC+TRC has been evaluated through simulations. We discuss the influence of RTPC+TRC on cooperative safety applications exemplarily for the forward collision warning (FCW) application.

The traffic control systems currently used in rail transportation are heavily infrastructure-based and therefore very costly. This work proposes a biologically inspired solution for the coordination of trains in dense railway networks, avoiding collisions with considerably higher cost efficiency than the state of the art solutions. This solution does not require track mounted infrastructure, instead it relies on the continuous cooperation between trains. Inspired by self-organizing biological systems, two simple algorithms are proposed for managing points of conflict or switches where the right of way or priority of trains has to be carefully handled. The first-level algorithm avoids local collisions by the exchange of status information through beacons. The second-level algorithm uses one-hop or multi-hop communication to share the network status among trains and coordinates the trains in possible conflict zones around switches or in shunting yards. The proposed solution can decrease the signalling cost of railway transport substantially. This efficient approach can significantly reduce the probability of accidents caused by human and hardware errors. In addition, the proposed approach can lead to significant time and energy savings in railway transport. The biologically inspired solution proposed in this paper might lead to a paradigm shift in the signalling system used in rail transportation.

The design of a collision avoidance system for trains implies the design of a MAC layer for their specific requirements. It should be efficient, reliable, use broadcast and support wireless mobile ad hoc networks (MANETs) with high user speeds. Therefore we are using awareness techniques, which allow a certain channel assignment, despite the absence of infrastructure. This paper presents a new MAC layer protocol designed for broadcast MANETs called COMB (Cell-based Orientation-aware MANET Broadcast). In principle, COMB allows the realization of a collision free transmission, high speed is supported and no handshake is required. COMB is based on localization aware cross layer dimensioned CDMA cells, and uses the SOTDMA protocol as intra cell scheme, while the inter cell scheme relies on direction and speed awareness.

This paper presents a channel model for direct train- to-train communication appropriate for the 400 MHz band. Extrapolation of theoretical and experimental results obtained for the planning of other railway communication systems like GSM-R is not obvious due to the difference in frequencies, antenna height and absence of base stations. In this paper, the analysis of the channel model covers different radio phenomena including path loss, Doppler, fading, and delay spread. Concretely we consider three scenarios (train stations, shunting yards and regional networks), for which the propagation channel characteristics are discussed. Furthermore, influence of special railway environments like cuttings which can be found near cities and towns, tunnels and bridges are encountered.