  This paper presents Balloon, a scalable blockchain consensus protocol which
could dynamically adapt its performance to the overall computation power
change. Balloon is based on a parallel chain architecture combined with a
greedy heaviest sub-chain selection strategy. It adopts an inovative block
sampling approach to assess the change of block generation rate in the network.
By introducing view change mechanism, Balllon is able to dynamically adjust the
number of parallel sub-chains. Balloon redefines the concept of block subtree
weight with view change in consideration, so that a total order of blocks could
be obtained safely. To deal with rapidly increasing block generation rate in
the blockchain network, participants of previous Nakamoto-style protocols are
required to continuously increase their mining difficulty so as to maintain an
expected security gurantee. Balloon, however, could accomadate a fixed
difficulty setup and assign superfluous block processing capability to new
sub-chains, which makes it more open and also economical.
