Optimized Power Distributions for Partitioned Signaling on Random Linear Matrix Channels

Iterative processing for linear matrix channels, aka turbo equalization, turbo demodulation, or turbo CDMA, has traditionally been studied as the concatenation of conventional error control codes with the linear (matrix) channel. However, in several situation, such as CDMA, the channel itself contains inherent redundancy, such as a repetition code contained in the direct-spread signature sequences of CDMA. For such systems, iterative demodulation of the linear channel exploiting the inherent code structure, followed by feed-forward conventional error control coding provides an efficient and powerful alternative, and outperform the more complex turbo CDMA methods for equal power modes (users). However, such equal-power systems are spectrally limited. In this paper optimized power distributions are derived and studied which allow arbitrary spectral efficiencies to be achieved with simple two-stage receivers.