Spectral Efficiency of Joint Multiple Cell-Site Processors for Randomly Spread DS-CDMA Systems

A chip-interleaved randomly spread direct-sequence code-division multiple-access (DS-CDMA) scheme is considered, employed in two variants of Wyner's infinite linear cell-array model with flat fading. Focusing on the asymptotic setup in which both the number of users per cell and the processing gain go to infinity, while their ratio (the “cell load”) goes to some finite constant, the spectral efficiencies of the optimum and linear minimum mean-squared error (MMSE) joint multicell receivers are investigated. A dramatic performance enhancement as compared to single-cell-site processing is demonstrated. The asymptotic behavior of the two receivers in extreme signal-to-noise ratio (SNR) regimes and in a high cell-load regime are analyzed as well. The impact of chip interleaving versus symbol interleaving is also investigated. Chip-level interleaving is found beneficial in several cases of interests, and is conjectured to be beneficial in general.