A survey

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In [21], it has presented a clear guideline of the benefits and drawbacks associated with different schemes. The authors do a review of the most relevant broadcast dissemination available in a fair comparative scheme analysis by evaluating them under the same environmental conditions, focusing on the same metrics, and using the same simulation platform, specially designed for VANETs, highlighting their features, and studying their performance under the same simulation conditions.

Others researches, in these cases with specifics subjects, such as [5], designed a collaborative virtual environment that covers the needs of integration of knowledge from different vehicles to endow the final user with the necessary information. The authors developed a model-driven approach that generates a groupware application for improving collaborative work and access to services. The implemented tool facilitates the development and implementation of collaborative frameworks in VANETs.

In [7], the authors have developed an interference-aware high-throughput channel allocation mechanism, called HT-CAM that addresses the unique challenges of CRVANETs. They create conflict graphs of link-band pairs to extract non-interfering OBU pairs that can communicate simultaneously on a given channel, increasing the spatial reuse of the available channels. In addition, this work formulates a high-throughput channel allocation problem as a MILP (Mixed-integer Linear Programming) problem, showing that the proposed HT-CAM provides with better network performances compared to state-of-the-art protocols.

Other specific related work [12] shows an analysis of several protocols proposed in the literature for message dissemination in VANETs. The authors proposed a protocol that sets the waiting time for relay candidates. They demonstrate that it is possible to reduce the delay needed to cover a given area. For that, they demonstrate that stopping beacon transmissions when a warning message detected does not provide a significant performance improvement. Nonetheless, by allowing a continuous channel access, it proves that the performance of any protocol might be greatly increased.

The state-of-art in VANETs is constantly developing, though much more research is requires, as many fundamental issues remains. This paper differs from others for the fresh information and solutions from different authors.

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CURRENT ISSUES AND PROPOSED SOLUTIONS

Many key important topics in VANETs are currently under intensive research and discussion. These issues and its background displays in this section.

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General Issues

The common issues for VANETs are limitation in bandwidth utilization, frequent link disconnection, small effective diameter, security and privacy, among others [19].

Issue 1: limitation in bandwidth utilization - There is no central coordinator that controls communication, channel congestion where bandwidth is limited to 10-20MHZ in high dense area. Time delay reduced by fair bandwidth utilization. If a vehicle wants to send message and there is no medium for transmitting then it has to wait, which leads to high latency. Bandwidth is important for the congestion control. Bandwidth utilization is very important for sending large amounts of information, otherwise will overload the system.

Issue 2: Frequent link disconnection - The link disconnects often due to high mobility, frequent fragmentation which results in increase in transmission power with throughput degradation.

Issue 3: Small effective diameter - Maintaining complete global topology is impossible due to weak connectivity between nodes and weak nodes connectivity and results in issue when applying existing algorithm.

Issue 4: Security and privacy – In VANETs vehicles connect with other random vehicles without knowing their intention; it brings vulnerability to the users. The receiver needs the trustworthy information it violates the above concern.

Issue 5: Routing protocols - Due to the above challenges designing an effective protocol, which transfers maximum packets in minimum time, is not possible. Scalability reduces conflict, Simultaneous operation of unicast routing request helps in packet delivery within shortest time during emergency critical path.

For those issues the proposed solutions are on Table 1.

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For Issue 1 the solution implemented with an algorithm that can control and detect the traffic congestion, i.e. paper [22], were only one message broadcasted by the vehicle, which reduces the overhead on the network improving bandwidth utilization.

In issue 2, it is possible to use the OLSR or its variations. OLSR is an optimization over a pure link state protocol as it compacts the size of data sent in the messages, and reduces the number of retransmissions to flood these messages in the entire network [23]. Today the OLSR has its variations i.e. a Meta-heuristic algorithm as paper [24], which is an optimization of OLSR protocol to enhance the performance of individual search method for optimization problem in VANETs.

For Issue 3, the proposed solution are position-based protocols, they assume that GPS device is equipped with vehicle in order to finds its own geographic position.

The solution for Issue 4 can be a combined group of protocols, but the choice was SMT protocol. The data transmitted in the communication between registered vehicles only. This protocol make sure that the vehicle ID is never. SMT utilizes MAC (Message Authentication Code) to check the integrity and authentication of its origin [13].

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Geo-localization

Currently, navigation technologies are GPS-dependent, which has several problems. The biggest one is directly connect with price, when you want an accurate GPS; if it is not expensive then there is imprecision of standard GPS devices, which become unusable for autonomous navigation [16].

Therefore, current researches intend to develop technology to obtain information about the position in real-time applications such as real time navigation, traffic behavior studies, and applications related to the location, such as forward collision warning application of the vehicle based central server [1].

In Fig. 1 we show the related issue that the next papers try to solve.

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