Improving minimum flow rate in wireless mesh networks by effective placement of directional antennas

Abstract

For some time, directional antennas have been considered to solve connectivity and interference issues in wireless networks. Several scenarios have been presented and often the conclusions drawn are positive, showing increase in capacity. However, to date there has been no effort to assess a holistic picture of the benefit/cost tradeoff and previous work mainly concerns either link scheduling or antenna placement but not the two combined. Such consideration will become increasingly important in the near future with the advent of heterogeneous networks and other possible combinations of mesh and public access networks. In order to better understand the full implications and potential of using directional antennas in such systems, we present a model for determining the maximized benefit/cost tradeoff using a combination of directional and omnidirectional antennas in wireless multihop backbones. We study the problem of maximizing the minimal flow rate from gateways to mesh routers in the mesh network. A mixed integer programming model is formulated for joint optimization of antenna placement and link transmission scheduling under an antenna-aware SINR interference constraint and a budget constraint. An accurate antenna model is used and variable modulation and coding schemes are used. The model is decomposed to a master problem and a pricing problem, and solved by a branch-and-price algorithm. Additionally, two effective heuristics are proposed as supplement methods. Applying the introduced model makes it possible to deploy directional antennas at appropriate nodes and find a corresponding link transmission scheduling (with data rate adaptation). The numerical results show that introducing directional antennas can indeed substantially improve the considered traffic objective. Interestingly, the results also show that it is not always optimal to install directional antennas at all possible nodes because of increased interference observed at non-receiving nodes within the beam width. Finally, comparisons are made to show the effectiveness of the proposed solution methods.