Piggy-back Network to Enable Beyond 5G Society Supported by Autonomous Mobilities: Transaction Record Management with DAG-based Distributed Ledger

This paper proposes a novel framework for transaction record management using distributed ledger technology over the “piggy-back network”, which is an opportunistic network composed of mid-range control plane and short-range data plane with heterogeneous wireless standards. In the network, mobile nodes such as service robots perform sensing by, e.g., recording video and try to disseminate the large-volume sensing data contents to other nodes via the data plane by a store-carryforward (SCF) principle. To manage the transaction records that represent event histories in the network, we employ a distributed ledger, where our previously proposed Proof-of-Forwarding (PoF) technique is used for block generation; a block is generated at the timing of completing data exchange. We design the ledger to have a directed acyclic graph (DAG) structure to work in an opportunistic network. By synchronizing the ledgers between nodes over the control plane, every node can grasp the differences of the databases owned by individual nodes, and this knowledge is utilized to determine if the node-to-node data exchange via the data plane is necessary. The computer simulations show that, compared to a conventional blockchain, the proposed DAG-based ledger can achieve a lower delay for disseminating transaction records across all nodes. In contrast, large delays are caused in a conventional blockchain system due to its single-branch structure.