This paper analyzes the problem of modeling the collisions in a distributed and heterogeneous fixed wireless network supporting multi-packet communication (MPC) by spatial reuse. In an MPC scenario, where multiple node pairs can be simultaneously active, the result of a transmission attempt is typically established using two main approaches: one, more idealized but suitable for theoretical analyses, based on a threshold on the number of sustainable communications, and another one, more realistic, relying on the signal-to-interference ratio (SIR) experienced by the receiving node. The two approaches may lead to considerably different results, since the number of allowed communications is often estimated neglecting many physical aspects. This study investigates this issue by presenting a mathematical model, validated by independent simulations, which relates the capture probability to the statistic of the SIR. The developed framework, which accounts in detail for the network topology and the antenna system characteristics of each node, is applied to an 802.11-based multi-packet scenario to evaluate the saturation throughput of an MPC network.
