Grassmannian Packings from Operator Reed-Muller Codes

This paper introduces multidimensional generalizations of binary Reed Muller codes where the codewords are projection operators, and the corresponding subspaces are widely separated with respect to the chordal distance on Grassmannian space. Parameters of these Grassmannian packings are derived and a low complexity decoding algorithm is developed by modifying standard decoding algorithms for binary Reed Muller codes. 

The subspaces are associated with projection operators determined by Pauli matrices appearing in the theory of quantum error correction and this connection with quantum stabilizer codes may be of independent interest. The Grassmannian packings constructed here find application in noncoherent wireless communication with multiple antennas, where separation with respect to the chordal distance on Grassmannian space guarantees closeness to the channel capacity. 

It is shown that the capacity of the noncoherent MIMO channel at both low and moderate SNR (under the constraint that only isotropically distributed unitary matrices are used for information transmission) is closely approximated by these packings. Index Terms Space-Time codes, Grassmannian packings, chordal distance, noncoherent MIMO channel, Reed-Muller codes.