“…In these works, the objective functions of the proposed optimization models are generally defined as (a) the minimization of end-to-end delay (eg, previous studies 4,5,[13][14][15][16][17][18] ), (b) the minimization of energy consumption (eg, previous studies 2,5,7,15,[18][19][20], and (c) the maximization of network lifetime (eg, previous studies 4, [21][22][23] ). Some constraints of these optimization models include the per-node flow-balance constraint (ie, flows are balanced at each node), the end-to-end flow conservation constraint (ie, every generated data are terminated at the sink node), the energy capacity constraint (ie, amount of energy consumed by nodes are limited), data-capacity constraint (ie, the capacity of each link is bounded), and the delay constraint (ie, end-to-end delay of the network is limited), which are either defined as separate constraints 2,7,9,20,[22][23][24] or incorporated into some constraints (eg, per-flow balance). [25][26][27] Some applications of optimization methods used in time-critical UASNs include routing protocol development 2,10,14,24,25 and optimal relay-node deployment.…”