## 7 Challenges and Open Issues  
The convergence of the Blockchain and IoV technologies brings out many opportunities, but it is not without its challenges and obstacles. One of these challenges, and probably the one that sparked the most research, is dealing with the resource constraints of devices in IoV networks, which limit the implementation of traditional Blockchain systems [46] (such as the one implemented under Bitcoin) because not only it requires high computational power, that the devices in IoV do not hold, it also requires high energy consumption. This requirement is not favorable on systems like IoV, where devices try to extend their battery life to the maximum. Given that most resource consumption comes from the consensus algorithm used by the Blockchain approach, research focuses on developing new algorithms or system architectures to reach consensus in these distributed environments while utilizing fewer resources.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Blockchain Platform** & **Type of Networks** & **Consensus Protocol** &
\begin{tabular}{c} **Programming** \\ **Language** \\ \end{tabular} & **Smart Contract Language** \\ \hline Hyperledger & Public (Ethereum) and & PoW, PoA, IBFT & Java & Truffle, Remix, web3j (Tools) \\ Besu & private networks & & & \\ Hyperledger & Public (optimal), private, & & & \\ Burrow & and consortium & & & \\ Hyperledger & Private & Various (pluggable) & Go & Golang (\textless{}1.0)/ \\ Fabric & Private & YAC & C++ & Various \\ Hyperledger & Private & Raft, PBFT, PoET & Various & Various \\ Sawtooth & Private & Raft, PBFT, PoET & Various & Solidity, Serpent, LLL \\ Ethereum & Public & PoW, PoS (2.0) & Various & Solidity, Serpent, LLL \\ Corda & Private & Various (pluggable) & Java & Java \\ Tezos & Public & PoS (delegated) & Various & Various (Michelson) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparison of Blockchain platforms.  
Mobility is also a great concern as frequent handovers can cause great delays in the network, which could decrease the efficiency, efficacy, and security of vehicles and applications, as decision-making results and notification alerts could be received with a delay that is not tolerable.  
For the specific use of UAVs, due to their autonomous properties, regulations have to be created to mitigate the issues related to:  
1. Real-life physics (aerodynamics, weather),
2. Technology development (sensors, actuators, types of engines, blades, wings),
3. Policy and laws (compliances, regulations, licensing),
4. Energy management (computing, engines versus battery),
5. Computing,
6. Standardization (protocols, services, networks, and data).  
The advance/delay of one front influences another. Accidents related to other aircraft's physical safety, UAV crashes in residential areas and parks, misuse of footage breaking people's privacy are some examples of situations that have modified regional policies and have driven the creation of regulations for UAVs.  
Smart cities are the hardest to implement and develop due to the complexity of the various technologies that intertwine to provide results, and due to the sheer scale, they have to work and deliver. The fact that it also depends on the development of emerging technologies (including, but not limited to, IoV and Blockchain) adding to the changes it requires on the city's physical distribution itself slows down the smart city concept development.