Consider an ad hoc wireless network, and assume that nine wireless nodes are arranged in a uniform grid as shown in the figure for the previous problem. Assume that each node has the same signal coverage and a circular shape represents the coverage (e.g., if the signal coverage is r meters then nodes 1 and 2 can transmit to each other but only if no other node is transmitting that is within r meters of the receiver). What is the minimum signal coverage so that none of the nodes suffer from the hidden terminal problem?