  While first-order channel statistics, such as bit-error rate (BER) and outage
probability, play an important role in the design of wireless communication
systems, they provide information only on the static behavior of fading
channels. On the other hand, second-order statistics, such as level crossing
rate (LCR) and average outage duration (AOD), capture the correlation
properties of fading channels, hence, are used in system design notably in
packet-based transmission systems. In this paper, exact closed-form expressions
are derived for the LCR and AOD of the signal at a receiver where maximal-ratio
combining (MRC) is deployed over flat Rayleigh fading channels in the presence
of additive white Gaussian noise (AWGN) and co-channel interferers with unequal
transmitting powers and unequal speeds. Moreover, in order to gain insight on
the LCR behavior, a simplified approximate expression for the LCR is presented.
As an application of LCR in system designs, the packet error rate (PER) is
evaluated through finite state Markov chain (FSMC) model. Finally, as another
application again by using the FSMC model, the optimum packet length to
maximize the throughput of the system with stop-and-wait automatic repeat
request (SW-ARQ) protocol is derived. Simulation results validating the
presented expressions are provided.
