Transmitter adaptation for CDMA systems via power control and code diversity

We consider a new transmitter adaptation scheme for direct sequence CDMA systems. In this new scheme, each user is given a number of codes (signature sequences). Each user transmits a data symbol via possibly more than one codes in each symbol interval. At the receiver, the contributions from different code channels are combined. Power control is applied to each code channel so that the signal-to-noise ratio (SNR) of the decision statistic satisfies the quality of service (QoS) requirement. Under our power control scheme, more power is supplied to the better code channels with less interference while less power is supplied to the poorer code channels. At the steady state, power is concentrated in the best code channels. Simulations show that systems with the new scheme often consume less power than standard CDMA systems with power control only. In many cases, the number of simultaneous users that can be supported is also increased.