This paper deals with the problem of diversity order analysis in a cooperative Amplify-and-Forward (AF) multiple-user networks. It is assumed that there are 2N terminals and a single destination (base station) and each terminal sends its information to the common destination. The terminals are simply divided into N sources and N relays based on the strength of direct channel between each terminal and the destination. Two different scenarios are proposed to assign the best relay to each weak-channeled terminal based on the instantaneous SNR information of the channels. In the first scenario, only the SNR of direct links between all terminals and the destination are known; whereas in the second scenario we assume that the SNR information of all channels are available. The main contribution of this paper is the analysis of diversity order improvement for each terminal through cooperation. Each scenario is analyzed separately. We have analyzed the terminal in the worst condition as a special case. The simulations are presented to confirm the results.