Improved Modeling of Highly Loaded UMTS Network with Nonnegative Constraints

In this paper, we deal with the power control problem in a non-uniform and highly loaded UMTS network with omnidirectional and smart antennas. If the pole capacity limit in a cell is exceeded no reasonable solution to the power control problem can be obtained with the methods such as the Gaussian elimination, Jacobi, Gauss-Seidel, SOR, or some Krylov subspace projection methods. In such a case, some users are usually removed from the system. In our approach, we solve a non-negatively constrained least square problem with very efficient gradient based linear solvers. This allows us to approximately estimate the powers of all the users even though a pole capacity is slightly affected in some cells. It can be implemented in radio resource management as an effective solution for networks in overload state. Additionally, to reduce a complexity of computation, we extend the dimension reduction technique proposed by Mendo and Hernando to the case of smart antennas. Our considerations are supported with some simulations based on a UMTS network model