On information theoretic aspects of multi-cell wireless systems

Some information theoretic aspects of cellular communication systems are addressed, focusing on a simple multi-cell model suggested by Wyner (1994). Accordingly, the system cells are ordered in an infinite linear array, and only adjacent cell interference is present, characterized by a single parameter 0 ≤ α ≤ 1. Starting with the downlink channel, it is assumed that only a single user is to be served in each cell. A linear joint preprocessing plus encoding scheme is proposed, which significantly enhances performance, while putting the complexity burden on the transmitting end. The approach is based on LQ factorization of the channel transfer matrix, combined with the "writing on dirty paper" approach (Costa (1983)) for eliminating the effect of uncorrelated interference, while fully known at the transmitter but unknown at the receiver. The attainable average rates with the proposed scheme approach those associated with receiver based optimum joint processing at the high SNR region. Extensions and applications are also discussed. Turning to the uplink channel, we investigate an optimally coded randomly spread DS-CDMA system with multiuser detection. The discussion is confined to asymptotic analysis where both the number of users per cell and the processing gain go to infinity, while their ratio goes to some finite constant. The spectral efficiency of various multiuser detection strategies is evaluated assuming single cell-site processing, and equal transmit powers for all users in all cells. Comparative results demonstrate how performance is affected by the introduction of inter-cell interference, and what is the penalty associated with the randomly spread coded DS-CDMA strategy.