  This paper applies a windowed frequency-domain overlapped block filtering
approach for the acquisition of direct sequence signals. The windows, as a
novel viewpoint, not only allow pulse shaping without a front end pulse shaping
filter, but also improve the performance of the spectrum sensing unit which can
efficiently be implemented into this frequency-domain receiver and may further
be used for spectrum sensing in cognitive radios or narrowband interference
cancellation in military radios. The proposed receiver is applicable for
initial time synchronization of different signals containing a preamble. These
signals include single carrier, constant-envelope single-carrier, multi-carrier
and even generalized-multi-carrier signals, which makes the proposed receiver
structure a universal unit. Furthermore, the receiver can be used to perform
filtering with long codes and compute the sliding correlation of an unknown
periodic preamble. It can further be modified to handle large Doppler shifts.
We will also demonstrate the computational complexity and analysis of the
acquisition performance in Rayleigh and Rician fading channels.
