In mobile networks, call admission control (CAC) is widely used in reaching of the quality of service (QoS) requirements. However, as the CACs schemes give priority to the handoff calls, the blocking probability is degraded. In this paper we propose a new scheme which is based on the combinaison of CAC scheme and load sharing policy between a cluster of surrounding cells. Our scheme forces some calls to handover, with conditions, to neighboring cells in order to avoid the blocking states in the serving cell. Thus we prove, in the case of one cell, that our scheme permits to improve both the dropping and blocking probabilities. We use multidimensional's Markov chains to model the systems because of the consideration of occupation and failure/reparations of channels. Therefore, it is difficult to deduce intuitively the relevance of our scheme versus others in the literatures. So, we apply a mathematical method based on stochastic comparisons in other to prove that our scheme provides better performance measures. We illustrate these proofs by numerical results in order to show the relevance of our mechanism to improve QoS of mobile networks.