Optimization of directional antenna network topology in Airborne Networks

Future IP-based Airborne Networks, important components in net-centric military communications, are envisioned to consist of a persistent backbone core network and dynamic tactical edge networks. The backbone would consist of quasi-stable platforms equipped with multiple high-capacity directional wireless links. The tactical edge networks would consist of highly dynamic platforms such as fighter jets equipped with omni-directional wireless links, and these would be interconnected by the backbone core network. Maintaining optimal backbone topology is an important problem with significant operational impact. Factors such as non-uniform link capacities, the number of traffic sources and sinks, and connectivity complicate the problem. The solution consists of making optimal selection of the link directionality and the possible insertion of communication relay nodes. We approach the solution by abstracting the network as a template from which to select the optimal combination of edges (transmitter-receiver pairs) and nodes (relays). Through innovative graph and flow-theoretic reductions we show that the single sink (or alternatively single source) case can be solved in polynomial time for uniform backbone link capacities. In contrast, we prove not only that the problem is NP-complete for non-uniform backbone link capacities but that the non-uniform case of the problem is hard to approximate to within even a logarithmic factor. Nevertheless we present a scheme based on iterative rounding that scales well in practice. Simulations demonstrate that our algorithm achieves a performance within a factor 2 of the theoretical best. This allows us to conclude that the use of algorithmic techniques in configuring backbone networks can contribute significantly in improving network performance.