Asymptotically optimal transmission power and rate control for CDMA channels with MF and MMSE receivers

The asymptotically combined optimal transmission power and rate control policy is derived for a DS-CDMA time varying fading channel with multiple user classes, random spreading codes and a receiver using either a conventional matched filter (MF) or a minimum mean square error (MMSE) multiuser detector. For a general objective function, the optimal policies are given by closed form functions of a single Lagrangian multiplier. The optimal policies are demonstrated by an application, where the transmission power is adapted to the channel fade variations, and the transmission rates are adapted to the tier containing the mobile. The effect of the number of tiers on the optimal transmission rate are presented for MF and MMSE receivers in an environment with Lognormal and Rayleigh fading. It is shown that with an MMSE receiver, there is a substantial increase in the total transmission rate, whereas only a negligible increase exists with a MF receiver.