In the planning and design of a Telecommunication System model a factor of importance is the channel. The deterioration to which the signal is exposed determines the QoS that a system can get, as well as also so much of the characteristic of the channel influence the design of the transmitter and receiver systems. A channel model that represents the behaviour of a propagation medium is an useful tool to analyze and evaluate systems under diverse conditions and situations. Here is presented the analysis of a system based on HAPS, using a model of channel considering semi-Markov random processes with 2 and 3 states. Results obtained in both cases are analyzed and compared.