Uplink Spectral Efficiency of Large, Distributed Antenna Systems With MMSE Processing

The spectral efficiency of a representative uplink in a wireless network with spatially distributed antennas and linear minimum-mean-square-error processing is found to approach an asymptote with a simple form as the number of antennas increases. These results generalize prior work which was applicable to systems with small numbers of base stations with large numbers of antennas each, to systems with large numbers of spatially distributed access points with small numbers of antennas each, and systems between these extremes. Additionally, these results are applied to systems where mobiles have multiple transmit antennas, and are used to characterize systems with both disjoint and user-centric clustering of cooperating base stations. Among other conclusions, these results indicate that with the same density and number of antennas cooperating to serve a mobile user, the uplink spectral efficiency with all antennas randomly distributed is several-fold higher than the case when the antennas are concentrated at one base station. These findings help improve our understanding of the tradeoffs involved in distributed antenna systems which have the potential to significantly increase data rates, but at a higher cost.