A scheduling framework for UWB & cellular networks

The max-min fair scheduling problem in wireless ad-hoc networks is a non-convex optimization problem. A general framework is presented for this optimization problem and analyzed to obtain a dual problem, which involves solving a series of optimization sub-problems. In the limit of infinite bandwidth (W --> infinity), the scheduling solution reduces to simultaneous transmission (spread spectrum) on all links [1]. This motivates the analysis of the scheduling problem in the Ultra Wide Band (UWB) regime (W much greater than 1, but finite), a model for certain practical radios. A quadratic (in 1/W) lower bound to the single link capacity function is developed, which simplifies the dual sub-problem to a quadratic optimization [2]. The solution to this sub-problem is then obtained under both total power and power spectral density constraints. This solution is utilized to iteratively construct the schedule (sub-band sizes) and power allocation, thus optimally solving the UWB max-min fair scheduling problem, to within any desired precision. Simulations on medium sized networks demonstrate the excellent performance of this scheme. A cellular architecture (not necessarily UWB) may also be considered in this framework. It is proved that Frequency Division Multiple Access is the optimal scheduling for a multi-band cellular architecture.