Performance of UTRA TDD ad hoc and IEEE 802.11b in vehicular environments

The FleetNet project aims at the development of a wireless ad hoc network for inter-vehicle communications (IVC). As a basis for the air-interface, the framework of the UMTS terrestrial radio access time division duplex (UTRA TDD) has been selected as the most promising candidate. Since UTRA TDD was developed for operation in a cellular network structure, modifications are required to enable mobile nodes to communicate in ad hoc mode without the existence of base stations. In particular, this comprises changes to physical (PHY) layer, medium access control (MAC) and radio resource management (RRM). The focus of this paper is the PHY layer of the air-interface and the resulting challenges in highly dynamic vehicular environments. The performance of the UTRA TDD ad hoc mode is assessed and compared to the IEEE 802.11b standard using link-level simulations. Results indicate that the UTRA TDD ad hoc PHY outperforms IEEE 802.11b in a typical highway scenario with very large relative velocities. In urban traffic environments with strong multipath propagation, IEEE 802.11b is not able to meet the required performance in terms of packet losses.