System and method for downlink communication

A method for communicating a command into a wellbore from the surface comprising:

• providing a downhole tool, the downhole tool coupled to a drill string, the drill string rotated by a top drive at the surface, the downhole tool including a downhole decoder and a drill string rotation rate sensor, the top drive controlled by a rotation controller;
• determining a command to be sent to the downhole tool;
• translating the command into a message, the message including a sequence of codes;
• selecting a set point RPM;
• encoding the message based on a predetermined encoding scheme, each code of the sequence of codes of the message encoded onto an RPM value, the RPM value offset from the set point RPM, or duration of a drill string rotation step;
• rotating the drill string substantially at the set point RPM for a predetermined duration;
• measuring the rotation rate of the drill string;
• determining by the downhole decoder that the rotation rate of the drill string remains generally constant for the predetermined duration to determine if a set point RPM has been received;
• identifying the received set point RPM with the downhole decoder;
• rotating the drill string consistent with a first code value of a first code of the message as encoded;
• decoding the first code;
• rotating the drill string consistent with a second code value of a second code of the message as encoded;
• decoding the second code;
• identifying the command from at least one of the decoded first and second code;
• and
• executing the command.