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Packet loss in vehicular networks can undermine the effectiveness of communication-based accident prevention systems. Traditionally, retransmission has been used to combat packet loss in communication networks. However, retransmission overhead is known to increase channel congestion in dense wireless vehicular networks, which increases the likelihood of packet loss due to collisions, limiting the loss recovery capacity of the retransmission algorithm. This paper presents a low-overhead retransmission algorithm called blind xor (BXOR). By xoring multiple packets into a single retransmission, BXOR recovers an increased number of lost packets per retransmission. BXOR keeps the overhead low by not trying to learn the loss status of the receivers via feedback, rather, which packets to xor are blindly decided by the retransmitter alone. It is mathematically proved that BXOR can outperform existing retransmission methods if the conditional reception probability (CRP) of the xored packets is greater than 0.5. The performance is maximized by xoring an optimal number of packets, which is a function of the CRP. It is also proved that there is a negative performance if BXOR is exercised for a CRP of less than 0.5. Guided by the analytical results, we propose a practical BXOR protocol, which opportunistically exercises the xor operation based on the current estimation of the CRP. Simulation experiments confirm that, within a 110-m radius of the original packet transmitter, BXOR can reduce the packet reception failure rate by up to 60% of the rates achievable by previously proposed retransmission algorithms. [ABSTRACT FROM PUBLISHER]

Cooperative positioning (CP) can potentially improve the accuracy of vehicle location information, which is vital for several road safety applications. Although concepts of CP have been introduced, the efficiency of CP under real-world vehicular communication constraints is largely unknown. Our simulations reveal that the frequent exchange of large amounts of range information required by existing CP schemes not only increases the packet collision rate of the vehicular network but reduces the effectiveness of the CP as well. To address this issue, we propose simple easily deployable protocol improvements in terms of utilizing as much range information as possible, reducing range broadcasts by piggybacking, compressing the range information, tuning the broadcast frequency, and combining multiple packets using network coding. Our results demonstrate that, even under dense traffic conditions, these protocol improvements achieve a twofold reduction in packet loss rates and increase the positioning accuracy of CP by 40%. [ABSTRACT FROM PUBLISHER]