This paper considers a multiuser broadband uplink massive multiple input multiple
output (MIMO) millimeter-wave (mmWave) system. The constant envelope orthogonal frequency
division multiplexing (CE-OFDM) is adopted as a modulation technique to allow an efficient power
amplification, fundamental for mmWave based systems. Furthermore, a hybrid architecture is
considered at the user terminals (UTs) and base station (BS) to reduce the high cost and power
consumption required by a full-digital architecture, which has a radio frequency (RF) chain per
antenna. Both the design of the UT’s precoder and base station equalizer are considered in this work.
With the aim of maximizing the beamforming gain between each UT and the BS, the precoder analog
coefficients are computed as a function of the average angles of departure (AoD), which are assumed
to be known at the UTs. At the BS, the analog part is derived by assuming a system with no multi-user
interference. Then, a per carrier basis nonlinear/iterative multi-user equalizer, based on the iterative
block decision feedback equalization (IB-DFE) principle is designed, to explicitly remove both the
multi-user and residual inter carrier interferences, not tackled in the analog part. The equalizer
design metric is the sum of the mean square error (MSE) of all subcarriers, whose minimization is
shown to be equivalent to the minimization of a weighted error between the hybrid and the full
digital equalizer matrices. The results show that the proposed hybrid multi-user equalizer has a
performance close to the fully digital counterpart.publishe
