  The period after the COVID-19 wave is called the Echo-period. Estimation of
crowd size in an outdoor environment is essential in the Echo-period. Making a
simple and flexible working system for the same is the need of the hour. This
article proposes and evaluates a non-intrusive, passive, and costeffective
solution for crowd size estimation in an outdoor environment. We call the
proposed system as LTE communication infrastructure based environment sensing
or LTE-CommSense. This system does not need any active signal transmission as
it uses LTE transmitted signal. So, this is a power-efficient, simple low
footprint device. Importantly, the personal identity of the people in the crowd
can not be obtained using this method. First, the system uses practical data to
determine whether the outdoor environment is empty or not. If not, it tries to
estimate the number of people occupying the near range locality. Performance
evaluation with practical data confirms the feasibility of this proposed
approach.
