  Millimeter wave (mmWave) communication in typical wearable and data center
settings is short range. As the distance between the transmitter and the
receiver in short range scenarios can be comparable to the length of the
antenna arrays, the common far field approximation for the channel may not be
applicable. As a result, dictionaries that result in a sparse channel
representation in the far field setting may not be appropriate for short
distances. In this paper, we develop a novel framework to exploit the structure
in short range mmWave channels. The proposed method splits the channel into
several subchannels for which the far field approximation can be applied. Then,
the structure within and across different subchannels is leveraged using
message passing. We show how information about the antenna array geometry can
be used to design message passing factors that incorporate structure across
successive subchannels. Simulation results indicate that our framework can be
used to achieve better beam alignment with fewer channel measurements when
compared to standard compressed sensing-based techniques that do not exploit
structure across subchannels.
