  Payment channel networks (PCNs) are one of the most prominent solutions to
the limited transaction throughput of blockchains. Nevertheless, PCNs suffer
themselves from a throughput limitation due to the capital constraints of their
channels. A similar dependence on high capital is also found in inter-bank
payment settlements, where the so-called netting technique is used to mitigate
liquidity demands.
  In this work, we alleviate this limitation by introducing the notion of
transaction aggregation: instead of executing transactions sequentially through
a PCN, we enable senders to aggregate multiple transactions and execute them
simultaneously to benefit from several amounts that may "cancel out". Two
direct advantages of our proposal is the decrease in intermediary fees paid by
senders as well as the obfuscation of the transaction data from the
intermediaries.
  We formulate the transaction aggregation as a computational problem, a
generalization of the Bank Clearing Problem. We present a generic framework for
the transaction aggregation execution, and thereafter we propose Wiser as an
implementation of this framework in a specific hub-based setting. To overcome
the NP-hardness of the transaction aggregation problem, in Wiser we propose a
fixed-parameter linear algorithm for a special case of transaction aggregation
as well as the Bank Clearing Problem. Wiser can also be seen as a modern
variant of the Hawala money transfer system, as well as a decentralized
implementation of the overseas remittance service of Wise.
