Asymmetric throughput problem due to Push-To-Talk (PTT) delays in CSMA/CA based heterogeneous Land Mobile Radio (LMR) networks

In this paper, we highlight the impact of variable Push-To-Talk (PTT) delays on performance of a heterogeneous Land Mobile Radio (LMR) network. We first present the PTT delay values and distributions observed for some commonly used LMR nodes. An analytical model is then developed to estimate the asymmetric throughput problem. The results obtained using this model and simulations show that a LMR node experiences a denial of service (DOS) due to collisions resulting from PTT delays. This leads to an asymmetry in throughput performance of individual nodes. The extent of the asymmetry is a function of total number of nodes in the system and the density of nodes with similar PTT delay profiles. These observations have implications in both, the performance and capacity planning of heterogeneous LMR network.