TABLE OF CONTENTS The MAC and the BC are information-theoretic abstractions of the uplink and the downlink of a single cell in a cellular system. However a cellular system consists of many cells with channels (timeslots, bandwidth, or codes) reused at spatially separated locations. Due to the fundamental nature of wireless propagation, transmissions in a cell are not limited to within that cell, and thus there is intercell interference between users and base-stations that use the same channels. The majority of current systems are interference limited rather than noise limited. As a result, it is not sufficient to exclusively study single-cell models and thus multi-cell environments must be explicitly considered in order to accurately assess the benefit of MIMO technology.
In this section we provide an overview of information-theoretic results for multi-cell environments. Analysis of the capacity of the cellular network explicitly taking into account the presence of multiple cells, multiple users, and multiple antennas, and the possibilities of cooperation between base-stations is inevitably a hard problem and runs into several long-standing unsolved problems in network information theory. However, such an analysis is also of utmost importance because it defines a common benchmark that can be used to gauge the efficiency of any practical scheme, in the same way that the capacity of a single-user link serves as a measure of the performance of practical schemes. Work on multi-cell environments can be grouped into two broad categories, with one group assuming that base-stations cannot cooperate (as is done in current...
