Opportunistic Channel Access Scheme for Cognitive Radio System Based on Residual White Space Distribution. This invention relates to wireless communication, and more particularly to channel access schemes. A node (called secondary node) and method for accessing a channel by the node in wireless communication networks is presented. The node is a lower priority node and senses the channel when the node has data to transmit, determines a maximum transmission duration on sensing the channel to be in an idle state so that the extent of interference with higher priority nodes (called primary nodes) is below a given threshold. The node then transmits the data within the maximum transmission duration. The occupancy of the channel due to the primary nodes is modeled as an Alternating Renewal Process (ARP) and the node uses a residual idle time distribution to determine the maximum transmission duration. FIG. 1