Controlled Synchronization of Independent Access Chains for CBDC Settlement

Central bank digital currency (CBDC) systems must support large-scale digital payment services while preserving centralized monetary control, operational resilience, and monetary consistency. However, direct central bank management of all user-level accounts and transactions may impose substantial operational and scalability burdens. To address this issue, this paper proposes BEA-CBDC, a hierarchical blockchain architecture based on the Base–Ecosystem–Access (BEA) framework with controlled synchronization. The base chain (BC) provides common anchoring infrastructure, the CBDC ecosystem chain (EC) maintains monetary authority and settlement control, and multiple access chains (ACs) independently manage user accounts and transaction requests. The CBDC EC coordinates independently timed AC operations through periodic controlled synchronization while retaining central bank authority over ecosystem-level settlement. The architecture is evaluated through protocol-level simulation of a large-scale CBDC environment with a fixed population of 108 user accounts under varying AC populations, transaction loads, temporary AC unavailability, and synchronization timing conditions. The results show that the proposed architecture supports distributed transaction processing under these operating conditions while allowing unresolved transactions to be carried over across settlement rounds. The aggregate CBDC quantity remained unchanged across all evaluated synchronization rounds, as expected from the monetary conservation invariant built into the settlement procedure under the specified operational assumptions. The timing-sensitivity results further indicate that the EC synchronization schedule should be configured in accordance with AC-side processing and communication capabilities. Overall, the results support the feasibility of the proposed controlled synchronization approach for hierarchical CBDC operation.