On the coding-spreading tradeoff and intra-cell frequency planning in uplink CDMA systems

We study potential gains in the spectral efficiency of multi-cell uplink CDMA systems that accrue from assigning users in different parts of a cell to different frequency bands. We develop a criterion that enables a fair comparison with a conventional (non-partitioned) system. Two design scenarios are considered: (i) each user requires a fixed data rate; (ii) each user has a fixed SNR. We show that in both scenarios there is a gain in spectral efficiency - regardless of the particular partitioning strategy employed f an MMSE receiver is used. There is no gain if a decorrelator or a matched filter receiver is used. We validate our results through numerical simulations and provide an intuitive explanation based on the coding-spreading tradeoff.