  In this paper, we present a first attempt to incorporate in the GNU Radio
ecosystem a tool called CycloDSP, devoted to the analysis of complex-valued
cyclostationary signals. Such signals are ubiquitous in communication and
signal processing, exhibiting periodic or almost periodic statistics that are
characterized by a countable set of cycle frequencies, which are related to the
main signal periodicities. Common cycle frequencies for modulated signals are
multiple of the baudrate and/or combination of the carrier frequency and
baudrate. Conventional estimation strategies for cyclostationary signal
analysis typically exhibit a high computational burden. Many approaches aimed
at reducing complexity exploit fast Fourier transform (FFT) algorithms, which
are very efficient for batch data but are not suited for continuously streaming
data, typically encountered in software-defined radio (SDR) applications. The
aim of this paper is to develop an out-of-tree (OOT) GNU Radio module
containing a set of building block functions, aimed at estimating functions,
such as the cyclic correlation functions, typically employed for
cyclostationary signal analysis. The proposed implementation must be designed
so as to ensure high efficiency in processing continuous data streams of
complex samples, both in terms of computational load and data storage, in order
to be executed on general purpose computers. We tested our implementation by
estimating in real-time the second-order cyclic statistics of a Gaussian
minimum-shift keying (GMSK) modulated signal, which belongs to a class of
signals commonly employed in aeronautical telemetry datalinks.
