We develop an approach through geometric functional analysis to error
correcting codes and to reconstruction of signals from few linear measurements.
An error correcting code encodes an n-letter word x into an m-letter word y in
such a way that x can be decoded correctly when any r letters of y are
corrupted. We prove that most linear orthogonal transformations Q from R^n into
R^m form efficient and robust robust error correcting codes over reals. The
decoder (which corrects the corrupted components of y) is the metric projection
onto the range of Q in the L_1 norm. An equivalent problem arises in signal
processing: how to reconstruct a signal that belongs to a small class from few
linear measurements? We prove that for most sets of Gaussian measurements, all
signals of small support can be exactly reconstructed by the L_1 norm
minimization. This is a substantial improvement of recent results of Donoho and
of Candes and Tao. An equivalent problem in combinatorial geometry is the
existence of a polytope with fixed number of facets and maximal number of
lower-dimensional facets. We prove that most sections of the cube form such
polytopes.Comment: 17 pages, 3 figure
