  Microwave backhaul links are characterized by high signal-to-noise ratios
permitting spectrally-efficient transmission. The used signal constellation
sizes and achievable data rates are typically limited by transceiver
impairments, predominantly by phase noise from non-ideal carrier generation. In
this paper, we propose a new method to improve the data rate over such
microwave links. We make use of the fact that adjacent frequency channels are
inactive in many deployment scenarios. We argue that additional data can be
transmitted in the skirts of the spectral mask imposed on the transmission
signal by regulation. To accomplish this task, we present a shaped wideband
single-carrier transmission using non-Nyquist pulse shapes. In particular, we
design spectrum-skirt filling (SSF) pulse shaping filters that follow the
spectral mask response, and perform detection using an accordingly increased
sampling frequency at the receiver. We evaluate the achievable information
rates of the SSF-based transmission considering practical dispersive channels
and non-ideal transmitter and receiver processing. To compensate for phase
noise impairments, we derive carrier phase tracking and estimation techniques,
and utilize them in tandem with nonlinear precoding which mitigates the
intersymbol interference introduced by the non-Nyquist SSF shaping filter.
Quantitative performance evaluations show that the proposed system design
achieves higher data rates in a dispersive microwave propagation environment
with respect to the conventional transmission with Nyquist pulse shaping.
