Access to reliable estimates of the wireless channel, such as the channel state information (CSI) and the received signal strength would open opportunities for timely adaptation of transmission parameters and consequently increased throughput and transmission efficiency in vehicular communications. To design the adaptive transmission schemes, it is important to understand the realistic channel properties, especially in vehicular environments where the mobility of communication devices causes rapid channel variation. However, getting CSI estimates is challenging due to the lack of support for obtaining CSI from the chipset. In this paper, we present our efforts towards enabling reliable, up-to-date channel estimates in vehicular communications. We begin by designing and conducting a measurement campaign where we collect IQ (inphase and quadrature) samples of the IEEE 802.11p transmission and implement CSI extraction algorithms to obtain and analyze wireless channel estimates from various real-world environments. We then propose a deep learning-based channel prediction for predicting future CSI and received signal levels. The trace-based evaluation demonstrates that our prediction approach improves the future power level estimate by 15% to 25% in terms of the root-mean-square-error compared to the latest known channel properties, thus, providing a sound basis for future efforts in anticipatory vehicular communication transmission adaptation. INDEX TERMS Channel state information, channel prediction, vehicular communications, neural networks, LSTM.

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Ensuring cooperative awareness by periodic message beaconing in vehicular environments is necessary to address pedestrian safety. However, high periodic basic safety message broadcasting in dense vehicular environments makes accessing the communication channel very competitive. Furthermore, high-frequency periodic broadcasting causes fast device energy dissipation which is a key issue for small computing devices used in wireless sensor and mobile communications. Therefore, in order to achieve reliable message dissemination for vehicle-to-pedestrian safety, energy loss minimization mechanisms for pedestrian mobile devices should be developed. This article proposes controlling the number of broadcasts by eliminating periodic safety message broadcasts from pedestrian nodes; these nodes only receive broadcasts from vehicles and then conditionally communicate with the vehicles when safety alerts are raised. When the pedestrian nodes do not receive messages from any vehicle for a specified period, pedestrian nodes broadcast a high-priority message advertising their position. Furthermore, for the pedestrian, adaptive message emission rates and transmission duration are proposed based on defined vehicle-to-pedestrian separation distances. This approach reduces the pedestrian device energy consumption and end-to-end delay and improves the packet delivery ratio compared to the vehicular broadcast approach for safety messages defined in the IEEE 802.11 standard.

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The IEEE 1609.4 legacy standard for multichannel communications in vehicular ad hoc networks (VANETs), specifies that the control channel (CCH) is dedicated to broadcast safety messages, while the service channels (SCHs) are dedicated to transmit infotainment service content. However, the SCHs can be used as an alternative to transmit high priority safety messages in the event that they are invoked during the service channel interval (SCHI). This implies that there is a need to transmit safety messages across multiple available utilized channels to ensure that all vehicles receive the safety message. Transmission across multiple SCHs using the legacy IEEE 1609.4 requires multiple channel switching and therefore introduces further end-to-end delays. Given that safety messaging is a life critical application, it is important that optimal end-to-end delay performance is derived in multichannel VANET scenarios to ensure reliable safety message dissemination. To tackle this challenge, three primary contributions are in this article: first, a cooperative multichannel coordinator (CMD) selection approach based on the least average separation distance (LAD) to the vehicles that expect to tune to other SCHs and operates during the control channel interval (CCHI) is proposed. Second, a model to determine the optimal time intervals in which CMD operates during the CCHI is proposed. Third, a contention back-off mechanism for safety message transmission during the SCHI is proposed. Computer simulations and mathematical analysis show that CMD performs better than the legacy IEEE 1609.4 and a selected state-of-the-art multichannel message dissemination scheme in terms of end-to-end delay and packet reception ratio.

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