In this article, we introduce a quantum key distribution protocol for the
line of sight channels based on coincidence measurements. We present a
proof-of-concept implementation of our protocol. We show that using coincidence
measurements to monitor multi-photon pulses results in a higher secure key rate
over longer distances for such channels. This key rate is higher than popular
implementations of quantum key distribution protocol based on BB84, for
example, the GLLP analysis [Quant. Info. Comput. \textbf{4}, 325 (2004)]. In
the experiment, we could generate around 74% more key bits per signal pulse
as compared to the GLLP analysis of BB84 protocol with similar parameters and
equal value of mean photon number.Comment: 12 pages, 4 figures and 3 tables. Final accepted version (Accepted
for publication in OSA Continuum
