Downhole electromagnetic network

A method of communicating between at least one surface system and a plurality of downhole tools using electromagnetic telemetry signals, the method comprising:

• communicating a plurality of electromagnetic telemetry signals between at least one surface system and a plurality of downhole tools using signal coordination control that coordinates transmission of the plurality of electromagnetic telemetry signals, wherein the downhole tools are mounted to corresponding drill strings or completion tubing or cable or attached onto the formation;
• and the at least one surface system is connected to at least one sensor that measures the signal between a pair of electrodes (or a plurality of electrode pairs) in electrical contact with the earth at different locations, the at least one surface system is configured to detect the uplink electromagnetic telemetry signals by measuring potential difference between a pair of electrodes (or a plurality of electrode pairs) in electrical contact with the earth at locations and in a manner assuring a substantial potential difference between the two electrodes, wherein the electrodes are selected from the group including a metal (conducting) stake in the ground, a metal fence or powerline pylon, well casing, blowout preventer, rig structure, a drill string, or the wellhead or casing of another well in the vicinity of the well with the downhole tool, and wherein:
• the signal coordination control determines at least one unique transmitting parameter for a corresponding electromagnetic telemetry signal communicated between the at least one surface system and a first downhole tool,
• the at least one unique transmitting parameter controls transmission of the corresponding electromagnetic telemetry signal, wherein the plurality of electromagnetic telemetry signals includes uplink electromagnetic telemetry signals that are transmitted by the downhole tools and propagate through a subterranean formation;
• and the at least one unique transmitting parameter controls transmission of a corresponding uplink electromagnetic telemetry signal, and
• the at least one unique transmitting parameter simultaneously suppresses interference between the corresponding electromagnetic telemetry signal and at least one other electromagnetic telemetry signal communicated between the at least one surface system and a second downhole tool.