  In ultra-dense small cell networks, spatial multiplexing gain is a challenge
because of the different propagation conditions. The channels associated with
different transmitreceive pairs can be highly correlated due to the i) high
probability of line-of-sight (LOS) communication between user equipment (UE)
and base station (BS), and ii) insufficient spacing between antenna elements at
both UE and BS. In this paper, we propose a novel transmission technique titled
Diversity Pulse Shaped Transmission (DPST) to enhance the throughput over the
correlated MIMO channels in an ultra-dense small cell network. The fundamental
of DPST is to shape transmit signals at adjacent antennas with distinct
interpolating filters, introducing pulse shaping diversity. In DPST, each
antenna transmits its own data stream with a relative deterministic time
offset-which must be a fraction of the symbol period-with respect to the
adjacent antenna. The delay is interpolated with the pulse shaped signal
generating a virtual MIMO channel that benefits from increased diversity from
the receiver perspective. To extract the diversity, the receiver must operate
in an over-sampled domain and hence a fractionally spaced equaliser (FSE) is
proposed. The joint impact of DPST and FSE helps the receiver to sense a less
correlated channel, eventually enhancing the UE's throughput. Moreover, in
order to minimise the spatial correlation, we aim to optimise the deterministic
fractional delay. Simulation results show that applying DPST to a correlated
channel can approximately enhance the UE throughput by 1.93x and 3.76x in 2x2
and 4x4 MIMO systems, respectively.
