  As a promising implementation model of payment channel network (PCN), payment
channel hub (PCH) could achieve high throughput by providing stable off-chain
transactions through powerful hubs. However, existing PCH schemes assume hubs
preplaced in advance, not considering payment requests' distribution and may
affect network scalability, especially network load balancing. In addition,
current source routing protocols with PCH allow each sender to make routing
decision on his/her own request, which may have a bad effect on performance
scalability (e.g., deadlock) for not considering other senders' requests. This
paper proposes a novel multi-PCHs solution with high scalability. First, we are
the first to study the PCH placement problem and propose optimal/approximation
solutions with load balancing for small-scale and large-scale scenarios, by
trading off communication costs among participants and turning the original
NP-hard problem into a mixed-integer linear programming (MILP) problem solving
by supermodular techniques. Then, on global network states and local directly
connected clients' requests, a routing protocol is designed for each PCH with a
dynamic adjustment strategy on request processing rates, enabling
high-performance deadlock-free routing. Extensive experiments show that our
work can effectively balance the network load, and improve the performance on
throughput by 29.3% on average compared with state-of-the-arts.
