The Wireless Sensor Network (WSN) uses autonomous sensor nodes to monitor a field. These sensor nodes sometimes act as relay nodesfor each other. In this paper, the performance of the WSN using fixed relay nodes and Multiple-Input Multiple-Output (MIMO) technology necessary for future wireless communication is evaluated in terms of the channel capacity of the MIMO system and the number of sensor nodes served by the system. Accordingly, we propose an optimum topology for the WSN backbone named Connected Relay Node Double Cover (CRNDC), which can recover from a single fault, the algorithms (exhaustive search and other two approximation methods) to find the optimum distance to place the relay nodes from sink node, and the height of the sink and relay nodes to be placed by using the pathloss model. The performances of different MIMO-WSN configurations over conventional WSN are evaluated, and the direct relationship between relay position and minimum required channel capacity are discovered.