Effects of Unintentional Denial of Service (DOS) Due to Push-to-Talk (PTT) Delays on Performance of CSMA/CA Based Adhoc Land Mobile Radio (LMR) Networks

Unintentional Denial of Service (DOS) problems occur in wireless networks such as Wi-Fi due to factors such as signal capture, interference and have been studied extensively in the literature. A similar problem manifests amongst nodes within a LMR network due to different PTT delay characteristics. We first present the typical PTT delay values and distributions followed by an analytical model to estimate the denial of service problem. The results obtained using the model and simulations show that the LMR nodes experience DOS due to collisions resulting from PTT delays. The results also show that there exists an asymmetry in the performance of individual nodes and the extent of this 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 performance and capacity planning of an adhoc LMR network.