# Blockchain-Based Licensed Spectrum Fair Distribution Method towards 6G-Envisioned Communications
## 3 BEAST System Model
### System Composition  
We implemented a blockchain-based prototype to demonstrate the feasibility of our method; the system composition is shown in Figure 1. The BEAST design principles and starting point can be summarized in the following three aspects.  
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2. Decentralization. In a traditional centralized LSA system, a band manager executes the function of controlling channels accessing and providing information of the channel state. The centralized solution is not suitable for the large scale of the 6G network  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Characteristics**} & \multirow{2}{*}{**Fairness**} & **Malicious Behavior** & \multirow{2}{*}{**Auditability**} & **Security and** \\  & & **Detection** & & **Privacy** \\ \hline
[15] & \(\surd\) & \(\times\) & \(\times\) & \(\times\) \\
[16] & \(\surd\) & \(\times\) & \(\times\) & \(\times\) \\
[17] & \(\times\) & \(\surd\) & \(\surd\) & \(\times\) \\
[18] & \(\times\) & \(\surd\) & \(\times\)  
and widely distributed network architecture. Decentralized architecture can reduce the computational load on the central servers and reduces the probability of a single point of failure.
2. Lightweight consensus. A proof of work (PoW) consensus mechanism costs a lot of computation overhead, and proof of stake (PoS) is weak to a coin age accumulation attack. To improve the instantaneity of spectrum distribution, a lightweight consensus protocol is needed.
3. Auditable. In most of the existing schemes, the participants are regarded as honest ones, whereas the MNOs, PBS and PUs are assumed to be rational participants according to the actual application scenarios in BEAST. PBS and PUs may violate the channel using regulations sometimes, as described in Section 1. In addition, MNOs may offer degraded accessing services when there are not sufficient available spectrum resources. For the above two dishonest behaviors, a surveillance and auditing mechanism is of great need.  
Based on the above three aspects of a demand analysis, we consider the BEAST in a 6G LSA network as a blockchain-enabled spectrum resource distribution mechanism. The system composition is shown in Figure 1. Under this framework, MNOs from different telecom operators intend to distribute the spectrum resources to the PBS and PUs, who are the spectrum consumers. They occupy the licensed channels themselves or redistribute the channels to the Second Users (SUs). The redistribution process is namely the secondary-level distribution. As shown in Figure 1, MNOs, PBS and PUs are connected using the consortium blockchain network. Compared to the public blockchain, the consortium blockchain can better fit for the 6G mobile network for its security and consensus efficiency. And only the nodes with sufficient computing power work as blockchain full nodes maintaining the global ledger, decreasing the maintenance cost. The rest of the nodes work as light nodes, and they can connect to and access the consortium blockchain through the full node. Compared to a traditional centralized LSA system, a smart contract on the consortium blockchain takes over the role of band manager to control channel accessing and provide channel state information in BEAST.  
Figure 1: BEAST system model.