This paper presents a theoretical model for investigating the average capacity of a millimeter wave (mmWave) communication link in line of sight conditions, when a fixed binary phase-shift keying (BPSK) or a quadrature PSK (QPSK) modulation is used and the nodes are distributed according to a homogeneous Poisson point process (PPP). In particular, as compared to the existing PPP approaches, which often consider the sole nearest neighbor as a possible destination, the proposed analysis enables to evaluate the link performance for a neighbor of any order, thus providing a more complete view of the achievable capacity. Besides, the adoption of the BPSK/QPSK modulations helps to obtain a more realistic estimation with respect to the ideal one provided by the usually adopted Shannon bound. Moreover, the derived formulas, which are expressed in analytical form and checked by extensive simulations, include the influence of all the main mmWave propagation phenomena: path-loss attenuation, small- and mid-scale fading. The developed model is specifically exploited to explore the impact of the average cell radius and of the selected frequency band on the sustainability of the mmWave link as the destination becomes farther from the source.
