A source node in a multihop network determines whether to transmit in a channel based on whether the channel is occupied by a packet transmission with a large number of relays; whether the source node is in the data tones back-off zone; and the source node is in the busy tone back-off zone. A multihop network transmits a packet including a RACH area and a hop number. The RACH area includes a list of subcarriers. A source node in the network dynamically determines the size of the RACH area. A node in the network performs an open-loop transmit power control.