# Blockchain for Future Wireless Networks: A Decade Survey
## 6 Open Issues and Research Challenges  
Blockchain is one of the promising technology to make a revolution in WNs. It has the advantages of transparency, traceability, decentralization, and high-security feature. However, there are some open research challenges and issues available while integrating the blockchain with WN. Figure 10 presents open security and privacy issues and research challenges in blockchain-enabled future WNs. Security mechanisms provided by 3 GPP have trustworthy links for non-malicious radio connectivity, but they cannot defend against DDoS and radio-electronic-based attacks. Blockchain nodes, consensus mechanisms, smart contracts, and wallets are key elements for enabling security in WN; however, attackers can find the core vulnerabilities from these elements and manipulate them. A summarized explanation of such open issues of blockchain-based WNs is discussed in detail as follows.  
* Double spending attack comprises spending of a single token multiple times by user over blockchain, which needs to be handled to secure WNs [3].
* Transactions are calculated in blockchain before they are accepted or rejected, which is done using consensus protocols. It is vulnerable to malicious activity, so it requires to be tested before deploying in the large-scale WN environment [14].
* Unauthenticated users can access wallets and exchanges using DDoS attacks. They successfully perform the theft of wallets.
* Malicious user controls more than 50% of nodes known as 51% attacks in the blockchain. Therefore, an attacker would be able to manipulate a user's information by introducing this type of attack [10].
* Sybil attack runs multiple malicious nodes on the network. They make restrictions for new nodes to access and add new blocks in the network [185].
* The problem of network deployment and interoperability comes when blockchain deploys in 5G and beyond networks with SDN, NFV, and MEC technologies that need to mitigate future WNs.
* Blockchain and smart contract in WNs facing leakage of transaction data privacy, smart contract logic privacy, and user privacy, which is also grabbing the attention of researchers [186].
* In permissioned blockchain, when nodes join the network, the system needs to ensure authenticity and authority, which raises concern for authentication and control over data [14].  
Some more research issues related to future WNs are also discussed that give future directions for further investigations, which are as follows.  
* In LTE networks, payload and control signalling are required to be encrypted, and the ratio between the amount of data transmitted and encryption overhead needs to be considered [187].
* Memory and resource consumption in large-scale networks is enormous. In addition, data collection, filtering, data sampling, and pre-processing are challenging because of heterogeneous data, which require security assurance and privacy protection [188].
* MIMO fulfills the requirements of services and data rate, but from a security point of view, resource allocation in MIMO needs to be elaborate.  
Figure 10: Open issues and research challenges.  
* To improve network traffic and security, it requires further investigations in beamforming [43].