Wireless Sensor Networks (WSN) typically consist of resource constrained micro sensors that organize itself into multi-hop wireless network. Sensors collect data and send it directly, or through intermediate hops in cooperative communication system, to the collection point. These sensors are powered up by batteries, for which the replacement or recharging is very difficult. With finite energy, the authors can transmit a finite amount of information. Therefore, minimizing the power consumption for data transmission becomes a most important design consideration for wireless sensor networks. In this paper, they discuss the optimal power consumption in cooperative wireless sensor network that are placed on a grid.