  Focusing on the downlink, we consider a base station (BS) and the cell it
covers. The Superposition Coding (SC), also referred to as Non Orthogonal
Multiple Access (NOMA), is implemented. We propose an analytical model of the
wireless cell covered by the BS. Based on this model, we establish a closed
form expression of the minimum transmit power of the base station, needed to
achieve a given SINR (signal to interference plus noise ratio), whatever the
users locations, on the area covered by the base station. The closed form
expression of the BS transmit power allows to establish quality of service
(QoS) and coverage values, in a simple and quick way.
