دانلود رایگان مقاله برنامه ریزی جغرافیایی انتقال جهتدار برای پیام ایمنی تناوبی در IEEE WAVE

Abstract

It is typically assumed that safety communication will use omnidirectional broadcast in vehicle-to-vehicle environments. However, in the IEEE Wireless Access in Vehicular Environment standard, some safety application messages will have directional semantics. For example, messages in the cooperative adaptive cruise control application are relevant to vehicles following the transmitter. In this paper, we investigate the impacts of using directional communication that is tailored to such applications. In particular, we show that the directional transmission indeed improves the message delivery probability by reducing message spillover in unnecessary directions. However, we also find that such benefit is not automatically obtained. Analysis reveals that it is crucial that the temporal ordering of the transmission is aligned with the vehicles’ spatial ordering to minimize the hidden terminal losses and fully garner the benefits of directional communication. For a method to ensure that the alignment takes place, we propose an application-level message scheduling solution that utilizes vehicle position information, and demonstrate that it leads to both lower channel utilization and higher message delivery rates than omnidirectional transmission.

4. Conclusion

In this paper, we explored the congestion control issue of directionally broadcast periodic safety messages. As directional transmission minimizes unnecessary traffic in the unwanted direction, we expected this to lead to reduced congestion and subsequently improved message delivery. However, we observed that directional transmission, when used alone, does not greatly improve the delivery performance, and can even worsen it. The reason for this disappointing phenomenon was confirmed to be the aggravated hidden terminal problem. We further found that, to minimize the adverse effects of hidden terminals, we should associate the temporal and spatial ordering of the message transmissions. Based on this finding, we designed a message scheduling algorithm that takes both into account. The proposed algorithm can be implemented at the application level using the existing information in exchanged beacon messages, such as the heading and vehicle position. Through extensive simulations of this application-level scheme, we have shown that directional transmission using the scheduling algorithm can achieve a significantly higher safety message delivery rate than omnidirectional messaging in the WAVE system. We also showed that the proposed scheme consumes less wireless resources, leaving more channel time to other applications.