Optimal downlink scheduling schemes for CDMA networks

The problem of allocating radio resources in the downlink of a CDMA network is studied. The modulation and coding schemes, numbers of multicodes, and transmit powers used for all mobile stations (MS´s) are jointly chosen so as to maximize the total transmission bit rate, subject to certain constraints. Based on the discrete and nonlinear nature of the proposed model, a mixed-integer nonlinear programming optimization problem is formulated. It is shown that the nonlinear relationship between bit rate and transmit power due to the use of different modulation and coding schemes and the maximum number of multicodes which can be assigned to an MS generally result in an optimal allocation which involves simultaneous transmission to several MS´s. In addition, it is shown that the optimal scheduler can yield a significant improvement in throughput by taking the MS traffic loads into account.