A Survey on the Roadmap to Mandate on Board Connectivity and Enable V2V-Based Vehicular Sensor Networks <s> Performance Comparison of IEEE 802.11p and LTE-V2V <s> This paper answers a simple but important question in VANET research: what is the optimal data rate to be used in DSRC-based vehicle safety communications? While it is generally accepted that the default choice is 6 Mbps, this assumption is not rooted in strong technical considerations. This paper provides a systematic evaluation of optimized data rates choices in a variety of scenarios. The answer found enables researchers to generally eliminate one dimension of complexity in relevant VANET studies. Additionally, the methodology used in this paper is possibly as interesting as the conclusion. <s> BIB001 </s> A Survey on the Roadmap to Mandate on Board Connectivity and Enable V2V-Based Vehicular Sensor Networks <s> Performance Comparison of IEEE 802.11p and LTE-V2V <s> With the increasing needs of the automotive industry, 3GPP is developing new functionalities in the long term evolution (LTE) cellular technology to specifically address vehicle-to-everything (V2X) connectivity, including in particular vehicle-to-vehicle (V2V) direct communications. At the basis of most enabled applications, either dealing with safety, traffic management or infotainment, it is of particular importance the cooperative awareness service, corresponding to messages sent periodically in broadcast by all vehicles to inform about their status and intentions. To optimize the usage of radio resources, allocations of packets are required to be smartly performed, following algorithms that currently represent a challenging open issue. Having in mind to face the design and validation of resource allocation in LTE-V2V networks when cooperative awareness is addressed, we implemented a simulator, called LTEV2Vsim, which will be shared with all the interested researchers. LTEV2Vsim is written in MATLAB and manages vehicles mobility either following simple models or more complex and realistic input files, and performs allocations following different implemented algorithms, both network controlled and autonomous. Finally, to demonstrate the possibilities of LTEV2Vsim, some example results are provided. <s> BIB002 </s> A Survey on the Roadmap to Mandate on Board Connectivity and Enable V2V-Based Vehicular Sensor Networks <s> Performance Comparison of IEEE 802.11p and LTE-V2V <s> To improve safety on the roads, next-generation vehicles will be equipped with short-range communication technologies. Many applications enabled by such communication will be based on a continuous broadcast of information about the own status from each vehicle to the neighborhood, often referred as cooperative awareness or beaconing. Although the only standardized technology allowing direct vehicle-to-vehicle (V2V) communication has been IEEE 802.11p until now, the latest release of long-term evolution (LTE) included advanced device-to-device features designed for the vehicular environment (LTE-V2V) making it a suitable alternative to IEEE 802.11p. Advantages and drawbacks are being considered for both technologies, and which one will be implemented is still under debate. The aim of this paper is thus to provide an insight into the performance of both technologies for cooperative awareness and to compare them. The investigation is performed analytically through the implementation of novel models for both IEEE 802.11p and LTE-V2V able to address the same scenario, with consistent settings and focusing on the same output metrics. The proposed models take into account several aspects that are often neglected by related works, such as hidden terminals and capture effect in IEEE 802.11p, the impact of imperfect knowledge of vehicles position on the resource allocation in LTE-V2V, and the various modulation and coding scheme combinations that are available in both technologies. Results show that LTE-V2V allows us to maintain the required quality of service at even double or more the distance than IEEE 802.11p in moderate traffic conditions. However, due to the half-duplex nature of devices and the structure of LTE frames, it shows lower capacity than IEEE 802.11p if short distances and very high vehicle density are targeted. <s> BIB003
In this section, we present some example results to compare the performance of the two main candidates, IEEE 802.11p and LTE-V2V. To provide example results in realistic conditions, we consider the road network layout of downtown Bologna; specifically, a portion of 1.8 × 1.6 km 2 has been simulated, corresponding to an area of 2.88 km 2 , as shown in Figure 3 . Traffic traces have been generated offline with a VISSIM micro-mobility simulator and given as an input to LTEV2Vsim BIB002 . An average number of 455 vehicles travel in the scenario and periodically exchange beacon messages of 300 bytes with a frequency of 10 Hz. As a performance indicator, we use the packet reception ratio (PRR), which is the ratio between the total number of successfully received messages and the total number of neighbors of each vehicle, where we consider neighbors of all those vehicles that have an Euclidean distance from the source below the given awareness range (i.e., the given distance). Concerning IEEE 802.11p, we evaluated the performance of MCS 3, which corresponds to the use of a quadrature phase shift keying (QPSK) modulation and a coding rate of 1/2 (i.e., 6 Mbps), suggested as the best compromise between range and duty cycle by BIB001 and, for comparison, MCSs 1 and 8, since MCS 1 corresponds to BPSK modulation and a coding rate of 1/2, providing the lower raw data rate (i.e., 3 Mbps), but the higher reliability and MCS 8 corresponds to 64-quadrature amplitude modulation (QAM), coding rate 3/4, providing the higher raw data rate (i.e., 27 Mbps), but the lowest coverage. MCS 3 is a somehow "average" best choice, but, if we assume a sparse network, the best choice would be to use MCS 1, which allows higher range, since the channel occupation would not be a problem; in the case of a road congestion, instead, maybe using MCS 8 could be a better trade-off for the range (which would not be a problem, given that cars move slowly and close to each other) with shorter transmissions over the wireless channel. Hence, we consider various MCS options. For the LTE-V2V system, we assume Sidelink Mode 4 (i.e., autonomous resource allocation) and different MCSs: MCS 4 and 7, corresponding to QPSK modulation and MCS 12 and 20, corresponding to 16QAM modulation. Similar considerations as those for IEEE 802.11p could also be applied for the choice of MCSs in LTE (further details on MSC and beacon resource (BR) allocation for LTE-V2V Mode 4 can be found in BIB003 .). For the channel model, we refer, for both IEEE 802.11p and LTE-V2V, to the one proposed by 3GPP, the Winner+ model B1, with shadowing log-normally distributed and having standard deviation of 3 dB in line of sight (LOS) and 4 dB in non line of sight (NLOS)  . The main settings are summarized in Table 3 . In Figure 4 , we plotted the PRR as a function of the transmitter-receiver distance for IEEE 802.11p and LTE-V2V varying the MCS. As expected, the curves are monotonically decreasing as the distance increases. It can be observed that the performance is highly affected by the adopted MCS and it is not easy a priori to predict which technology outperforms the other. For distances lower than 50 m, both of the technologies provide a PRR close to 1 and then LTE-V2V outperforms IEEE 802.11p when adopted with a MCS lower than 20. By adopting LTE-V2V with MCS = 20, the PRR is very similar to that of IEEE 802.11p with MCS 1 and 3 up to 100 m; then, IEEE 802.11p outperforms LTE-V2V. The worst performance, in this urban scenario, is provided by IEEE 802.11p with MCS = 8 since, as is known, it has the lower reliability in terms of covered distance; in fact, its PRR falls rapidly after 50 m of distance between the transmitter and the receiver. 