A wireless modem for communication in a network of wireless modems (25M i) via a communication channel, the wireless modem comprising: a transceiver assembly; transceiver electronics comprising: transmitter electronics to cause the transceiver assembly to send wireless signals into the communication channel; receiver electronics to decode signals received by the transceiver assembly; at least one processing unit (44, 56) executing instructions to: enable the transmitter electronics to transmit an identification signal into the communication channel, receive data from at least one other wireless modem via the receiver electronics indicative of a unique identifier identifying the other wireless modem and a power supply supplying power to the transceiver assembly and the transceiver electronics, characterized in that the at least one processing unit (44, 56) in addition executes instructions to: receive data indicative of at least one local sensor measurement of an environmental condition related to the depth of the other wireless modem below the surface of the Earth, and determine the at least one of the position and the relative order of the other wireless modem using the relation between the data indicative of the local sensor measurement and the depth of the other wireless modem below the surface of the Earth. a transceiver assembly; transceiver electronics comprising: transmitter electronics to cause the transceiver assembly to send wireless signals into the communication channel; receiver electronics to decode signals received by the transceiver assembly; at least one processing unit (44, 56) executing instructions to: enable the transmitter electronics to transmit an identification signal into the communication channel, receive data from at least one other wireless modem via the receiver electronics indicative of a unique identifier identifying the other wireless modem and a power supply supplying power to the transceiver assembly and the transceiver electronics, characterized in that the at least one processing unit (44, 56) in addition executes instructions to: receive data indicative of at least one local sensor measurement of an environmental condition related to the depth of the other wireless modem below the surface of the Earth, and determine the at least one of the position and the relative order of the other wireless modem using the relation between the data indicative of the local sensor measurement and the depth of the other wireless modem below the surface of the Earth. transmitter electronics to cause the transceiver assembly to send wireless signals into the communication channel; receiver electronics to decode signals received by the transceiver assembly; at least one processing unit (44, 56) executing instructions to: enable the transmitter electronics to transmit an identification signal into the communication channel, receive data from at least one other wireless modem via the receiver electronics indicative of a unique identifier identifying the other wireless modem and a power supply supplying power to the transceiver assembly and the transceiver electronics, characterized in that the at least one processing unit (44, 56) in addition executes instructions to: receive data indicative of at least one local sensor measurement of an environmental condition related to the depth of the other wireless modem below the surface of the Earth, and determine the at least one of the position and the relative order of the other wireless modem using the relation between the data indicative of the local sensor measurement and the depth of the other wireless modem below the surface of the Earth. enable the transmitter electronics to transmit an identification signal into the communication channel, receive data from at least one other wireless modem via the receiver electronics indicative of a unique identifier identifying the other wireless modem and a power supply supplying power to the transceiver assembly and the transceiver electronics, receive data indicative of at least one local sensor measurement of an environmental condition related to the depth of the other wireless modem below the surface of the Earth, and determine the at least one of the position and the relative order of the other wireless modem using the relation between the data indicative of the local sensor measurement and the depth of the other wireless modem below the surface of the Earth.