(A) study on optimal scheduling in CDMA packet radio networks

Abstract

In this thesis, we examine the problem of the time slot assignment in a CDMA network using a TDMA slot allocation in the case of arbitrary multiple reception capacity. A mathematical formulation and a solution procedure using Lagrangean relaxation method are proposed. In the classical TDMA model it is assumed that whenever two or more packets attempt transmission simultaneously, a collision occurs and none of the packets is received correctly. But in a CDMA packet radio the situation is quite different. By using orthogonal codes CDMA can provide the nodes with a higher reception capacity. Our object is to find fair and correct slot allocation with the smallest possible number of slot, that is, with minimum frame length. "Fair" means that every nodes should have the same number of slots in a cycle. "Correct" means that for any different two nodes, there must be a slot which is assigned one but not assigned to the other and any slot can be assigned to at most $\rho$ nodes, where $\rho$ is a given possitive integer. Our algorithm is not efficient with respect to the computational time but the solution from our algorithm is close to the optimal solution than other method. Computational experiments are performed to support our algorithm and show that our algorithm give better performance.