Heterogeneous wireless networks are characterized by mobile nodes having distinct communications capabilities with respect to data rate, radio range, frequency band, battery life, etc. Scalability is one of the most important factors governing the efficacy of heterogeneous wireless networks. We present an approach specifically designed to improve the scalability of OLSR, rendering it more suitable as a routing protocol for large-scale heterogeneous wireless ad hoc networks. Our approach organizes the hierarchical structure dynamically while making full use of the various components in a military network or civilian network, and the hierarchical scheme presented is fully integrated within the existing OLSR protocol. With this hierarchical structure we propose optimizations to OLSR to reduce the amount of control traffic generated and to make more efficient use of the higher capacity links in the network. Furthermore, the hierarchical structure releases the OLSR from having to perform frequent routing computations, as the local movement of member nodes is now handled within the cluster, without affecting other parts of the network.

The OPNET simulation results show that HOLSR (Hierarchical OLSR) does scale more efficiently: the overhead is dramatically reduced, and protocol performance is greatly improved with respect to packet-delivery ratio and end-to-end delay of data packets. With the hierarchical approach, we not only retain the advantage of OLSR - the connection setup delay is minimized - but also improve two aspects of the protocol: 1) overhead is further reduced and 2) frequent route updates are avoided. Thus, for large heterogeneous ad hoc networks, HOLSR yields very promising results.

Papers:

• Y. Ge, L. Lamont, L. Villasenor. "Improving Scalability of Heterogeneous Wireless Networks with Hierarchical OLSR", The OLSR Interop & Workshop, San Diego, USA, August 2004.