Inter-vehicle communication promises to increase movement and behavior awareness of vehicles compared to existing technologies like radar. The idea is that every vehicle regularly transmits information such as position, speed and heading in Cooperative Awareness Messages (CAMs) to surrounding vehicles. The periodic CAMs are foreseen to be sent via 5.9 GHz IEEE 802.11p ad-hoc communication.

While the properties of this direct ad-hoc communication have been intensively investigated in recent years, knowledge about radio propagation at inner-city intersections with potential Line-Of-Sight (LOS) obstruction was scarce at the start of this thesis, although the suboptimal radio propagation properties due to the relatively high frequency of 5.9 GHz impact radio-coverage in this scenario.

Furthermore, cellular systems---in principle also able to handle the information exchange---promise a better coverage in the inner-city intersection scenario due to the high position of base stations and a lower frequency. The potential limitations of ad-hoc communication on the one hand and possible advantages of cellular communication on the other hand motivate to compare the suitability of both communication technologies in a challenging communication environment.

A scenario investigation revealed that cross-traffic assistance at inner-city intersections represents the desired high demand scenario. It relies on the capacity-intense regular CAM exchange and needs a high status update rate, raising capacity concerns especially in cellular networks. Furthermore, a building placement analysis shows that Non-Line-Of-Sight (NLOS) reception is needed in this scenario in terms of ad-hoc communication.

In order to tackle the lack of knowledge on 5.9 GHz NLOS propagation, an extensive NLOS measurement campaign was performed at eight intersections in the city of Munich. A systematic selection of measured intersections enabled the detailed evaluation of certain influence factors on NLOS reception quality. The measurements revealed that NLOS reception is well feasible at application critical distances to intersection center. In a second step, a dedicated 5.9 GHz NLOS path loss and fading model was deduced. Multi-dimensional fitting enabled a reliable quantification of the identified influence factors. A comparison to existing models shows that they mostly differ substantially to reality at 5.9 GHz.

Finally, NLOS reception quality under network competition is being evaluated by performing packet-level network simulations, leveraging the proposed NLOS propagation model. The simulations revealed that high transmission power levels are usable in critical traffic conditions. While reception rates in NLOS are degraded due to network competition, the resulting reception quality seems still tolerable.

In terms of cellular communication, capacity, latency and costs are major concerns. The capacity demand of the investigated application in a cellular system is investigated by an environment analysis. It combines information about base station position, street network, and vehicle flow on streets in order to predict the number of communicating vehicles, and in a second step the inter-vehicle communication driven network load per cell. A high load demand of several thousand CAM/Cell/s is identified.

Available capacity and resource efficient delivery of CAMs are evaluated by a technical analysis of the Universal Mobile Communication System (UMTS) and Long Term Evolution (LTE) cellular standards. Cell broadcasts in the downlink and a random access driven uplink delivery are proposed to prevent duplication overhead in the downlink and potentially under-utilized static connections. While UMTS does not provide sufficient capacity, LTE does due to its higher spectral efficiency and ability to use wider frequency bands. UMTS is characterized by a high latency, while LTE round trip times turn out reasonably low. In conclusion, LTE can enable cross-traffic assistance from a technical perspective.

However, modifications at base stations would be required to support the proposed efficient delivery. Furthermore, a non-negligible amount of bandwidth consumption is found, directly translating into considerable operational costs.

Finally, the ability of ad-hoc and cellular communication to enable cross-traffic assistance at inner-city intersections is compared based on the found results. While both systems can technically enable the application, ad-hoc communication provides a slight advantage regarding latency and reliability. More importantly however, utilizing ad-hoc communication inherits a considerable cost advantage compared to a cellular communication based information delivery.