Mesh Network Topology Construction and Channel Frequency Allocation in the TOWN Project

M Me es sh h N Ne et tw wo or rk k T To op po ol lo og gy y C Co on ns st tr ru uc ct ti io on n a an nd d C Ch ha an nn ne el l F Fr re eq qu ue en nc cy y A Al ll lo oc ca at ti io on n i in n t th he e T TO OW WN N P Pr ro oj je ec ct t T TI IK K-R Re ep po or rt t 2 25 55 5 Executive Summary The TOWN project addresses employing mesh routers with multiple IEEE 802.16-2004 interfaces to construct self-organized backhaul telephony networks for public safety scenarios. Given this context, this report reviews TOWN specific requirements, and proposes to decompose the self-organized network construction problem to a topology construction problem and a channel allocation problem. This decomposition allows us to draw a relation from the channel allocation problem to the well known max-k-cut problem in graph theory. A key property of the max-k-cut problem is that this problem is known to be NP-hard. This means that it is not feasible to compute the optimal channel allocation at non-trivial scenario sizes. However, even after discussion with widely-recognized communication theory experts such as Roger Wattenhofer from ETH Zurich and Stefan Nilsson from KTH Stockholm, we do not see any simpler modeling of the problem that this decomposition. This report thus reviews related work and proposes a pragmatic approach that is based on combining heuristic algorithms/schemes that approximate the optimal solutions for the topology construction and channel allocation problem. This approach of iterating topology construction and channel allocation until a reasonable solution is found has the potential to achieve viable results for self-organized mesh network construction. However, another consequence of this modeling is that it may not be possible to determine how much space for optimization will be left although we can and certainly will evaluate the performance of the proposed algorithms/schemes. Thus, optimizing and tuning the heuristic algorithms will be an important issue in the future. We expect that with more precise information about the application scenarios considered by ASCOM, the optimization focus can be made smaller and the algorithms can be improved towards better performance.