Title: On Information Theoretic Aspects of Multi-Cell Wireless Systems
Speaker: Shlomo Shamai (Shitz), Professor of Electrical Engineering, Technion--Israel Institute of Technology
Date: Thursday October 3, 2002 4:30 pm
Location: Princeton University, Friend 004
Some information theoretic aspects of cellular communication systems are addressed, focusing on a simple model suggested by Wyner (1994), of a linear cell array. Accordingly, it is assumed that the system cells are ordered in an infinite linear array, and that only adjacent cell interference is present, characterized by a single parameter alpha. Starting with the downlink channel, it is assumed that only a single user is to be served in each cell (which is equivalent to intra-cell TDMA, or orthogonal DS-CDMA, and is in fact optimal in the non-fading environment). The channels are assumed to be either non-fading, or slowly changing ergodic flat fading channels. A linear pre-processing plus encoding scheme is proposed, which significantly enhances cellular downlink performance, while putting the complexity burden on the transmitting end. The approach incorporates the ``writing on dirty paper' result (Costa (1983)) and some variants for eliminating the effect of uncorrelated interference, being fully known at the transmitter but unknown at the receiver. The attainable average throughput of the proposed scheme is optimal and approaches that associated with optimum joint processing at the high SNR region. Turning to the uplink channel, and assuming Rayleigh flat-fading, we examine attainable rates with various single and multiple cell processing strategies. We proceed then to investigate an optimally coded randomly spread DS-CDMA system with single-cell site, 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 (with and without fading), and what is the penalty associated with the randomly spread coded DS-CDMA strategy. Extensions, and related problems deserving further attention will also be shortly discussed.
The talk is based on joint works with Benjamin Zaidel, EE Dept. Technion, Haifa Israel and Sergio Verdu, EE. Dept. Princeton University
Seminar Sponsored by DIMACS Special Focus on Computational Information Theory and Coding.