Understanding Interference

David Tse Wireless Foundations U.C. Berkeley

Interference management is a central issue in wireless system design
but a fundamental understanding has been lacking from an information
theory point of view.  In this talk we  discuss recent progress in
this direction, from both a microscopic and from a macroscopic point
of view.

First,  we look at a simple model of two interfering wireless links.
This is the classical Gaussian interference channel, the capacity of
which is open for 30 years.  We present a very simple scheme that
can achieve to within a single bit the capacity for all values of
the channel parameters. Using this result, we characterize precisely
the interference-limited behavior of the system and show explicitly
the potential performance gain over more traditional techniques such
as orthogonalizing and treating interference as noise.

Second, we look at large-scale ad hoc networks and ask how much
interference limits the information theoretic capacity scaling of
such networks. The seminal result by Gupta and Kumar shows that with
classical decode-and-forward architecture and treating interference
as noise, the total capacity scales at most like the square root of
the number of nodes. The capacity is limited by mutual interference
between communicating nodes. We show that in contrast, with
intelligent node cooperation and distributed MIMO communication,
interference can be completely mitigated and the capacity can scale
linearly with the number of nodes.  The key ingredient is a
hierarchical and digital architecture for nodal exchange of
information for realizing the cooperation.
