Feasibility of Multipath Construction in mmWave Backhaul

This paper focuses on the problem of finding multiple paths with relay nodes to maximize throughput for ultra-high-rate millimeter wave (mmWave) backhaul networks in urban environments. Relays are selected between a pair of source and destination base stations to form multiple interference-free paths. We first formulate the problem of feasibility of multi-path construction as a constraint satisfaction problem that includes constraints on intra-path and inter-path interference and several other constraints that arise from the problem setting. Based on the derived equations, we transform the multiple paths construction problem into a Boolean satisfiability problem. This problem can then be solved through use of a satisfiability (SAT) solver, which however results in a very high running time for realistic problem sizes. To address this, we propose a heuristic algorithm that runs in a fraction of the time of the SAT solver and finds multiple interference-free paths using a modification of a maximum flow algorithm. Simulation results based on 3-D models of a section of downtown Atlanta show that the heuristic algorithm finds multiple paths in almost all the feasible cases (those where the SAT solver succeeds in finding a solution) and produces paths with higher average throughput than the SAT solver. Furthermore, the heuristic increases throughput by 50-100% in typical cases compared to a single-path solution.