A method for characterizing a communication channel on a communication network includes receiving within a network node at least one silent symbol transmitted together with a packet, and determining within the network node the amount of energy received by the network node during the silent symbol. Determining the amount of energy may include comparing the amount of energy received during a first silent symbol with the amount of energy received during subsequent silent symbols. The packet transmitted with the silent symbol may include a preamble and the silent symbol may be transmitted before the preamble. The packet may include data symbols and the silent symbol may be transmitted for a duration that is shorter than the duration of one data symbol transmitted in the packet.