  The upcoming fifth generation (5G) New Radio (NR) interface inherits many
concepts and techniques from 4G systems such as the Orthogonal Frequency
Division Multiplex (OFDM) based waveform and multiple access. Dimensioning 5G
NR interface will likely follow the same principles as in 4G networks. It aims
at finding the number of radio resources required to carry a forecast data
traffic at a target users Quality of Services (QoS). The present paper attempts
to provide a new approach of radio resources dimensioning considering the
congestion probability, qualified as a relevant metric for QoS evaluation. We
distinguish between the spatial random distribution of indoor users, modeled by
a spatial Poisson Point Process (spatial PPP) in a typical area covered by a 5G
cell, and the distribution of outdoor users modeled by a linear PPP generated
in a random system of roads modeled according to a Poisson Line Process (PLP).
Moreover, we show that the total requested Physical Resource Blocks (PRBs)
follows a compound Poisson distribution and we attempt to derive the explicit
expression of the congestion probability by introducing a mathematical tool
from combinatorial analysis called the exponential Bell polynomials. Finally we
show how to dimension radio resources, for a given target congestion
probability, by solving an implicit relation between the necessary resources
and the forecast data traffic expressed in terms of cell throughput. Different
numerical results are presented to justify this dimensioning approach.
