  Ever increasing number of cellular users and their high data requirements,
necessitates need for improvement in the present heterogeneous cellular
networks (HetNet). Carrier sensing prevents base stations within a certain
range of the transmitter from transmitting and hence aids in reducing the
interference. Non-orthogonal multiple access (NOMA) has proven its superiority
for the 5th generation (5G) networks. This work proposes a mathematical model
for an improved HetNet with macro base station (MBS) and femto base station
(FBS) tier. The FBS tier is equipped to support NOMA and carrier sensing for
its transmissions. Offloading is performed for load balancing in HetNet where
the macro users (MU) from congested MBS tier are offloaded to the FBS tier. The
FBS tier pairs the offloaded MU (OMU) with an appropriate pairing user (PU) to
perform NOMA. The performance of the OMU is studied under different channel
conditions with respect to the available PU at the FBS and some useful
observations are drawn. A decrease in outage probability by $74.04\%$ for cell
center user (CCU) and $48.65\%$ for cell edge user (CEU) is observed for low
density FBS. The outage probability decreases by $99.60\%$, for both the CCU
and CEU, for high density FBS using the proposed carrier sensing in NOMA. The
results are validated using simulations.
