  Node selection is a simple technique to achieve diversity and thereby enhance
the physical layer security in future wireless communication systems which
require low complexity. High-speed data transmission often encounters frequency
selective fading. In this context, we evaluate the exact closed-form expression
for the ergodic secrecy rate (ESR) of the optimal source-destination pair
selection scheme with single-carrier cyclic-prefix modulation, where the
destination and eavesdropper channels both exhibit independent frequency
selective fading with an arbitrary number of multipath components. A simplified
analysis in the high-SNR scenario along with an asymptotic analysis is also
provided. We also derive and compare the corresponding results for the
sub-optimal source-destination pair selection scheme. We show that our analysis
produces the corresponding ESR results under narrowband independent
Nakagami-$m$ fading channel with any arbitrary integer parameter $m$. The
effect of transmitters, destination and eavesdropping paths correlation on the
ESR is also demonstrated. Our solution approach is general and can be used to
find the ESR of a wider variety of transmitter selection schemes.
