# Blockchain-Based Licensed Spectrum Fair Distribution Method towards 6G-Envisioned Communications
## 3 BEAST System Model
### System Process
The 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. A lack of consensus certainty will lead to an uncertain delay in transaction confirmation, which is not applicable for a nearly real-time 6G spectrum distribution scenario. For the following two considerations, we design a PoT consensus mechanism instead of PoW and PoS. First, the trust value is the representation of spectrum usage behavior, and the trust value can be regarded as a reference for spectrum distribution priorities. Second, compared to other consensus mechanisms, PoT is a lightweight and efficient consensus mechanism. Inspired by the research results in [26], a lightweight consensus mechanism, PoT, for blockchain-based spectrum distribution is proposed in this section. And the PoT consensus establishment mechanism is described. We list the basic assumptions in the following. **Assumption 1**. : _The consortium blockchain network for 6G spectrum distribution is partially synchronous, which is the same as the Bitcoin network [4]._

**Assumption 2**. : _We assume that the consortium blockchain network is an ideal network in terms of reliable connection and a low-latency broadcast channel._

The core idea of PoT is to ensure that each node in the consortium blockchain network maintains an agreed upon trust value ledger, recording the trust value of each user. Bitcoin adopts the PoW consensus protocol. The first node that solves the hard problem obtains the right to publish the block, and other nodes verify the block. In the PoT consensus protocol, the node with the highest trust value generates the block and publishes it. The block is verified with the validators who are nominated using the leader. A PoT consensus process diagram is illustrated in Figure 2. Under this architecture, the consortium blockchain ledger management organization includes three roles, the leader, candidates and followers. As shown in Figure 3, the consensus process includes the following four stages. In Stage 1, a leader election and nominating validating group members are completed. If a certain candidate receives enough votes from the majority peers, then they become a leader legally. And they will lead the consensus procedure until the end of their term. The newly elected leader first nominates a list of transaction validators and broadcasts the list to the consortium blockchain. Each of the nominated validator's trust value should be bigger than a predefined threshold, \(\mathit{Tr}_{th}\). The main task finished in Stage 2 is to pack transactions into the next block with the validating nodes. The current height of the block \(h\) is encrypted with each validator's public key, \(pk_{v}\), using the leader, generating ciphertext, \(C_{h}\). If a member on the 6G network receives the message and can decrypt \(C_{h}\), then they are a legal validator. In Stage 3, the message is first decrypted and broadcasted to the consortium blockchain. Second, the message is sent to the 6G network. Each consortium ledger management node recovers the voted transactions for each validator. Each consortium ledger management node votes on the transactions. Finally, the leader in their term will count the votes and package the verified transactions. In Stage 4, the nodes that hold and maintain the ledger first recover the voted transactions. Then, the nodes vote on the verified transactions. The leader chooses the transactions with the majority of votes and determines the sequence of the transactions that have occurred. In the end, the transactions are uploaded and published on the consortium blockchain. Simultaneously, a unique token is authorized to the corresponding user to access to the 6G network. Through the above design, the online trust value has the similar function of digital currency. And the trust value is agreed upon by every participant and cannot be manipulated by third parties.