  Wireless backhaul is considered to be the key part of the future wireless
network with dense small cell traffic and high capacity demand. In this paper,
we focus on the design of a high spectral efficiency line-of-sight (LoS)
multiple-input multiple-output (MIMO) system for millimeter wave (mmWave)
backhaul using dual-polarized frequency division duplex (FDD). High spectral
efficiency is very challenging to achieve for the system due to various
physical impairments such as phase noise (PHN), timing offset (TO) as well as
the poor condition number of the LoS MIMO. In this paper, we propose a holistic
solution containing TO compensation, PHN estimation, precoder/decorrelator
optimization of the LoS MIMO for wireless backhaul, and the interleaving of
each part. We show that the proposed solution has robust performance with
end-to-end spectral efficiency of 60 bits/s/Hz for 8x8 MIMO.
